Article

DNA transfer-a never ending story. A study on scenarios involving a second person as carrier

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Abstract

The transfer of DNA directly from one item to another has been shown in many studies with elaborate discussions on the nature of the DNA donor as well as material and surface of the items or surrounding features. Every DNA transfer scenario one can imagine seems to be possible. This evokes more and more intricate scenarios proposed by lawyers or attorneys searching for an explanation of the DNA of a certain person on a distinct item with impact on a crime. At court, the forensic genetic scientist has to comment on the probability of these scenarios thus calling for extensive studies on such settings. Here, the possibility of an involvement of a second person as a carrier of the donor's DNA in a variety of different scenarios including three pairs of people and two kinds of items (textiles and plastic bags) was investigated. All transfer settings were executed with and without gloves on the carrier's hands. DNA left on the items was isolated and analyzed using the Powerplex® ESX17 kit. In 21 out of 180 samples, all alleles of the donor DNA could be obtained on the second item (12 %), on eight samples, the donor's DNA was dominant compared to all other alleles (38 % of samples with complete donor profile). Additionally, 51 samples displayed at least more than half of the donor's alleles (28 %). The complete DNA profile of the carrier was found in 47 out of 180 samples (42 partial profiles). In summary, it could be shown that a transfer of donor DNA from epithelial cells through a carrier to a second item is possible, even if the carrier does not wear gloves.

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... It is also known that cell material, such as epithelial cells from the surface of the skin can be transferred between individuals or objects; skin cells from individual A can be transferred to individual/object B (primary transfer) and possibly on to a surface C (secondary transfer) [2,6,7]. Following allegations of penile penetration and detection of the victim's DNA on the defendant's penis, the defendant may display an alternative explanation to the DNA findings, i.e. that he touched the victim's skin with his hands and subsequently transferred the victim's cells to his penis during a bathroom visit. ...
... The area under the curve (AUC) is 0.93, which indicate a good predictive ability for the model. (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11) and each replicate. The results are categorized by the three different localizations on penis: Glans, shaft and sulcus at two different activity situations: "mucous" = samples collected from penis after contact with vaginal mucous membrane cells (direct transfer), and "skin" = samples collected from penis after social contact (secondary transfer). ...
... Bar plot displaying the number of observed female and male alleles in the DNA profiling result for each couple(1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11) and each replicate, categorized by the three different localizations on penis: Glans, shaft and sulcus at two different activity situations: "mucous" = samples collected from penis after contact with vaginal mucous membrane cells (direct transfer) and "skin" = samples collected from penis after social contact (secondary transfer). ...
Article
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In alleged sexual assault and rape cases, the focus has often been to collect samples from the victim's body, for detection of body fluids or skin cells from the offender. But in many cases intimate body samples from the perpetrator(s) can also be informative. However, in cases where the female victim claims vaginal penetration, the defendant may display an alternative explanation to the DNA findings, i.e. that the victim’s skin cells has been secondarily transferred to his penis. We hypothesized that female DNA will be detected in a significantly greater amount on swabs from penis after intercourse than after secondary transfer by skin contact. Fourteen male-female couples were recruited to test the above hypothesis, by collecting penile swabs from 3 specified anatomical locations: Glans, shaft, and the coronal sulcus, after two different situations: Vaginal intercourse and secondary transfer of epithelial cells by skin contact. The results show that penile swabs following intercourse produce significantly higher DNA concentrations than after secondary transfer by skin contact. Our results, indicates which of the anatomical regions is best suited for sampling. The DNA profiling results show a preponderance of female profiles over male profiles following intercourse compared to secondary skin contact. Based on these data, it is possible to make a statistical model to distinguish between samples taken after intercourse and samples taken after secondary transfer by skin contact based on the amount of female DNA and mixture proportion (Mx) between female and male DNA in samples collected from penis swabs.
... Depending on the source of the DNA as well as the conditions at the crime scene, the answer to the second question is quite difficult. While several studies deal with the possibilities of DNA transfer [e.g., [6][7][8][9], studies on the persistence of DNA are still rare and have mostly been conducted under laboratory conditions [10][11][12][13]. Investigations of outdoor scenarios are mainly limited to restricted conditions [14][15][16][17][18][19]. ...
... Using 2 µl DNA-containing solutions each sample was analyzed in duplicates. DNA amplification with multiplex PCR Kit Powerplex® ESX17fast, evaluation on an ABI3500 Genetic Analyzer (Applied Biosystems) with GeneMapper® ID-X Software, and assessment of results regarding complete profiles were done as described before [9]. In short, a result was regarded as a complete profile, if in every evaluable locus every allele of the cell donor was found. ...
Article
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DNA persistence and DNA transfer are important features in the assessment of a crime scene. The question how long DNA may persist at a certain location is similarly important as the one how the DNA has been transferred to this location. Depending on the source of the DNA as well as the conditions at the crime scene, the answer to this question is quite difficult. In this study, persistence of DNA from epithelial abrasions, blood cells, and saliva cells in indoor and outdoor scenarios has been investigated with regard to exposure time and exposure conditions including sunlight, temperature, and humidity in summer and winter scenarios. Overall, we generated 338 epithelial samples, 572 blood samples, and 572 saliva samples. A complete profile of the cell/DNA donor after exposure could be obtained in 47%, 65%, and 58% of epithelial abrasions, blood samples, and saliva samples, respectively. Regarding blood samples, there were no differences between supporting materials cloth and plastic; however, the percentage of complete profiles was higher for saliva samples on plastic and for epithelial samples on cloth. In indoor scenarios, complete profiles could be recovered from nearly all blood and saliva samples up to 9 months, whereas the amount of epithelial complete profiles already started to decline after 3 months. In outdoor scenarios, we observed a tipping point at an exposure time of 3 months. Blood and saliva samples collected after this period displayed complete profiles in less than 25% of samples. After 12 months, no outdoor sample showed a complete profile. The results of this study facilitate decisions on the relevance of recovered DNA from crime scenes.
... The owner of the office was detected in 60 of the 75 (80 %) samples from which profiles were able to be analysed: 12x as the only contributor, 29x as a major, 12x as a majority contributor and 7x as a minor contributor. When the office owner was observed as the only, the major or the majority contributor, the LRs ranged from 4 to 4 × 10 23 . Of the 53 profiles where the office owner was the sole, major or majority contributor, the temporary occupier of the office was also present as a minor component in 12 of these (16 % of interpretable profiles). ...
... Notably, the highest DNA yield and number of contributors retrieved was from chairs for both laboratories; chair seats for Lab A and chair backrests for Lab B. Reasons for this could be due to these surfaces being the largest within the experiment, having been sampled using tape lifts in Lab B, and being the surfaces touched for the longest duration, as well as them being the only fabric surfaces sampled. Several studies have shown that in general, fabric substrates pick-up and retain DNA better than non-porous substrates [20][21][22][23]. Furthermore, the relatively higher number of contributors to profiles generated from the chair seats and backrests may indicate that clothing picks up DNA from locations it comes into contact with and transfers some of it to these items when the person wearing the clothing sits on the chair, where it can accumulate [18,24]. ...
Article
There is a need to improve our awareness of the transfer, persistence, prevalence and recovery of DNA (DNA-TPPR) from items/surfaces, and within different spaces and circumstances, to assist sample targeting during collection and activity level assessments. Here we investigate DNA-TPPR within office spaces. Specifically, to what extent DNA, left by a temporary user of an office space that has been occupied by a regular user for an extended period, is detectable when the duration of their temporary occupancy and their general activities are known. Also, how readily the DNA of the regular user is still detectable after a known period of occupancy by another person, and to what extent DNA of others is present. Samples were collected from 18 core items/surfaces within eight single use office spaces that had been used temporarily by another occupant for 2.5-7 h. Four of these offices were within one forensic laboratory and four within another. Each lab collected and processed the samples to generate DNA profiles using their own set of methodologies. The owner/regular user of an office space was found to be the major/majority contributor to profiles from most items within the space, even after temporary use by another person. The detectability of the temporary occupier of an office space varied among offices and items. The temporary occupier was not observed on all items touched. In most instances, when detected, the temporary occupier was known to have touched the surface at some stage. Therefore, where one is seeking to collect samples that may detect a temporary user of a space, it is advisable to target several potentially touched sites. A difference in methodologies applied from collection through to profiling appears to impact DNA yields and profile types. Ascertaining the impact of using different methodologies on the profiles generated from collected samples, requires further research. More research is also needed to generate data to help determine frequency estimates for different types of profiles given different user histories of an item or space.
... Partial profiles also occurred only rarely in samples from the table surface (13% of samples), but more often on the textile (35%; Figure 1). These results are in line with findings in other studies, in which rough absorbent material like cotton is described as more DNA affine than smooth surface like plastic [1,10,11,[26][27][28]. The use of soap led to a slight reduction of DNA amount (on average 0.0037 ng/μl without soap and 0.0026 ng/μl with soap) as well as percentage of partial profiles (45% without and 25% with soap). ...
... Only 46% of samples (mean value of experiments with and without soap) demonstrated a complete profile, a further 38% (mean value) at least a partial profile. A possible explanation for these differences is that the high DNA affinity of textile surfaces as well as the seeping of the saliva into the upholstery probably prevented an extensive dispersal [1,10,11,[26][27][28]. ...
Article
DNA transfer in aqueous solutions as well as the persistence of DNA on washed items has become a major subject of research in recent years and is often a significant problem in court. Despite these approaches, the question about the “mobility” of DNA especially in capital offenses cannot be answered in every case, since a variety of scenarios for DNA transfer are possible. The aim of this study was to investigate whether DNA traces could be distributed by cleaning an object. For this purpose, a large table surface and fabric piece were artificially provided with skin contact traces and body fluids (saliva and blood) in two series of experiments and then wiped off with water or with soap water (218 samples in total). These experiments resulted in a clear “carry over” of DNA traces especially for body fluid samples (100% of blood samples and 75% of saliva samples led to a complete profile). The results could be confirmed in a second experimental set-up with 384 samples using different cleaning agents and more intense cleaning actions. Even small amounts of 5–10 μl body fluid led to complete profiles in around 45% of the samples, while 20 μl led to nearly 65% complete profiles. A strong impact of the amount of traces and the chosen surface could be demonstrated, while the active component of the cleaning agent seemed to be of less influence with the explicit exception of chloric agents which rendered almost everything completely DNA-free. In summary, a distribution of DNA traces by wiping or scrubbing an object could be clearly proven.
... Though, in general, both is possible, especially since the users did not wash their hands prior to the experiment in order to reflect realistic conditions. There were several cases of (partly) masked touching described in the literature, where either people transferred nonself DNA without leaving a detectable or relevant amount of self DNA [9,10,15,17,18,41] or touched a surface without leaving self DNA behind allowing that a background DNA on that surface is detected instead [5,6,9,10,14,32,34]. These events justify the defense's hypothesis of an unknown and undetected burglar. ...
... Another study observed as well DNA being transferred even if gloves were worn. The authors suggested that the DNA might be transferred via garment to the outside of the glove [41]. ...
Article
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Experts are increasingly concerned by issues regarding the activity level of DNA stains. A case from our burglary-related casework pointed out the need for experiments regarding the persistence of DNA when more than one person touched a tool handle. We performed short tandem repeat (STR) analyses for three groups of tools: (1) personal and mock owned tools; (2) tools, which were first "owned" by a first user and then handled in a burglary action by a second user; and (3) tools, which were first owned by a first user and then handled in a moderate action. At least three types of tool handles were included in each of the groups. Every second user handled the tool with and without gloves. In total, 234 samples were analyzed regarding profile completeness of first and second user as well as properties like detectable major profile or mixture attributes. When second users simulated a burglary by using a tool bare handed, we could not detect the first user as major component on their handles but attribute him to the stain in 1/40 cases. When second users broke up the burglary setup using gloves, the first user matched the DNA handle profile in 37% of the cases. Moderate use of mock borrowed tools demonstrated a material-dependent persistence. In total, we observed that the outcome depends mainly on the nature of contact, the handle material, and the user-specific characteristics. This study intends to supplement present knowledge about persistence of touch DNA with a special emphasis on burglary-related cases with two consecutive users and to act as experimental data for an evaluation of the relevance of alleged hypotheses, when such is needed in a court hearing.
... STR profiles of such mixtures typically display more than two peaks per STR locus [64]. Even DNA transferred indirectly may become detectable and confound the DNA profile of a perpetrator [63,65]. ...
Article
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Modern PCR-based analytical techniques have reached sensitivity levels that allow for obtaining complete forensic DNA profiles from even tiny traces containing genomic DNA amounts as small as 125 pg. Yet these techniques have reached their limits when it comes to the analysis of traces such as fingerprints or single cells. One suggestion to overcome these limits has been the usage of whole genome amplification (WGA) methods. These methods aim at increasing the copy number of genomic DNA and by this means generate more template DNA for subsequent analyses. Their application in forensic contexts has so far remained mostly an academic exercise, and results have not shown significant improvements and even have raised additional analytical problems. Until very recently, based on these disappointments, the forensic application of WGA seems to have largely been abandoned. In the meantime, however, novel improved methods are pointing towards a perspective for WGA in specific forensic applications. This review article tries to summarize current knowledge about WGA in forensics and suggests the forensic analysis of single-donor bioparticles and of single cells as promising applications.
... glass and plastic). In recent years, even the possibility of a tertiary transfer has been discussed leading to further speculations as to how DNA is deposited at crime scenes [19]. ...
Article
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Over recent years, DNA profiling techniques have become highly sensitive. Even small amounts of DNA at crime scenes can be analysed leading to new defence strategies. At court, defence lawyers rarely question the existence of a DNA trace (source level) but challenge how the DNA was transferred to the scene (activity level). Nowadays, the most common defence strategy is to claim that somebody else had stolen the defendant’s gloves and used them while breaking and entering. In this study we tested this statement. Using gloves made of different material (cloth, leather, rubber) and varying secondary transfer surfaces (wood, metal, glass), we simulated a few of the most likely transfer scenarios that occur during breaking and entering. While we detected the presence of DNA on the outside of 92 of the 98 gloves tested, we observed only one case of secondary transfer in a total of 81 transfer experiments. This data demonstrates that secondary transfer under conditions resembling realistic conditions is a very rare event.
... Studies have been published on the effectof the substrate material, primarily the surface of the touched item or skin, on deposition of DNA. Touch DNA profiles are more likely to be developed from porous substrates, such as wood or fabric, than nonporous substrates, such as glass (Daly et al., 2012;Helmus et al., 2016). The texture or "roughness" of the substrate surface likely influences the amount of skin cells deposited. ...
Article
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Historically, evidence collection in sexual assault cases focused on obtaining foreign contributor bodily fluids through swab collection. With improvements in deoxyribonucleic acid (DNA) analysis methods, DNA profiles can be developed from touch DNA and applied to sexual assault cases. Following a literature review on factors affecting touch DNA transfer, a groping case study with innovative evidence collection is presented to support the expansion of touch DNA evidence collection in sexual assault cases. The groping case led to the development of a statewide sexual assault touch DNA form to guide evidence collection. DNA findings from additional groping sexual assault cases are reported to further show and justify the importance of evidence collection in groping cases. Implications on multidisciplinary practices are summarized to promote evidence collection and analysis in groping sexual assault cases. As forensic nurses are educated to accurately collect DNA evidence and provide trauma-informed, patient-centered care, they are best suited to provide nursing care for patients who have experienced groping sexual assaults. Optimal DNA findings in groping and sexual assault cases are best achieved through development of strong multidisciplinary, collaborative relationships between forensic nurses and forensic scientists.
... Various methods of comparison have been used in the literature: including counting self vs non-self alleles, mixture proportions and DNA quantities recovered [2,9,19,20,21,22,23]. However, mixtures commonly include background DNA from unknown contributors which interfere with positive identification of POI alleles. ...
Preprint
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Bayesian logistic regression is used to model the probability of DNA recovery following direct and secondary transfer and persistence over a 24 hour period between deposition and sample collection. Sub-source level likelihood ratios provided the raw data for activity-level analysis. Probabilities of secondary transfer are typically low, and there are challenges with small data-sets with low numbers of positive observations. However, the persistence of DNA over time can be modelled by a single logistic regression for both direct and secondary transfer, except that the time since deposition must be compensated by an offset value for the latter. This simplifies the analysis. Probabilities are used to inform an activity-level Bayesian Network that takes account of alternative propositions e.g. time of assault and time of social activities. The model is extended in order to take account of multiple contacts between person of interest and 'victim'. Variables taken into account include probabilities of direct and secondary transfer, along with background DNA from unknown individuals. The logistic regression analysis is Bayesian - for each analysis, 4000 separate simulations were carried out. Quantile estimates enable calculation of a plausible range of probabilities and sensitivity analysis is used to describe the corresponding variation of LRs that occur when modelled by the Bayesian network. It is noted that there is need for consistent experimental design, and analysis, to facilitate inter-laboratory comparisons. Appropriate recommendations are made. The open-source program written in R-code ALTRaP (Activity Level, Transfer, Recovery and Persistence) enables analysis of complex multiple transfer propositions that are commonplace in cases-work e.g. between those who cohabit. A number of case examples are provided. ALTRaP can be used to replicate the results and can easily be modified to incorporate different sets of data and variables.
... The possibility of a second person as a carrier was studied in various ways. DNA was found to transfer from donor to cotton to plastic or cotton via a second person 40% of the time in 180 samples examined [112]. An investigation into the deposition and persistence of directly and indirectly transferred DNA on regularly used knives sought to check whether intrinsic qualities of profiles could distinguish between directly and indirectly transferred DNA [113]. ...
Article
Full-text available
This review paper covers the forensic-relevant literature in biological sciences from 2016 to 2019 as a part of the 19th Interpol International Forensic Science Managers Symposium. The review papers are also available at the Interpol website at: https://www.interpol.int/content/download/14458/file/Interpol%20Review%20Papers%202019.pdf.
... However, since DNA is everywhere and indirect transfer may occur, obtaining a touch DNA profile from an evidence does not necessarily place the donor of this DNA at the crime scene [2,3]. The number of scenarios that may have led to the deposition of the detected DNA have been substantially increasing. ...
Article
Improvements in scientific techniques allowed the analysis of limited amounts of DNA and the testing of not only body fluids but also touch DNA. The possibility of DNA transfer often raises the question of how the DNA was deposited: directly or by indirect transfer? Therefore, it is important to comprehend the factors that can influence it. Our study shows that background DNA and DNA indirect transfer are in fact a reality, having the potential to interfere with target DNA detections, and corroborates that area of contact and type of material are of importance on DNA transfer.
... When similar substrates were applied in secondary transfer experiments conducted by Verdon et al. [74] and Fonneløp et al. [60], results were consistent with those of Goray et al. [37,38]. Furthermore, studies by Goray et al. [37], Daly et al. [75], Fonneløp et al. [60] and Helmus et al. [76] also found differences in the quantities of DNA directly transferred by hands depending on the type of substrate, observing that more DNA was transferred to wood and fabric than glass, metal or plastic. ...
Article
Understanding the variables impacting DNA transfer, persistence, prevalence and recovery (DNA-TPPR) has become increasingly relevant in investigations of criminal activities to provide opinion on how the DNA of a person of interest became present within the sample collected. This review considers our current knowledge regarding DNA-TPPR to assist casework investigations of criminal activities. There is a growing amount of information available on DNA-TPPR to inform the relative probabilities of the evidence given alternative scenarios relating to the presence or absence of DNA from a specific person in a collected sample of interest. This information should be used where relevant. However, far more research is still required to better understand the variables impacting DNA-TPPR and to generate more accurate probability estimates of generating particular types of profiles in more casework relevant situations. This review explores means of achieving this. It also notes the need for all those interacting with an item of interest to have an awareness of DNA transfer possibilities post criminal activity, to limit the risk of contamination or loss of DNA. Appropriately trained forensic practitioners are best placed to provide opinion and guidance on the interpretation of profiles at the activity level. However, those requested to provide expert opinion on DNA-related activity level issues are often insufficiently trained to do so. We advocate recognition of DNA activity associated expertise to be distinct from expertise associated with the identification of individuals. This is to be supported by dedicated training, competency testing, authorisation, and regular fit for purpose proficiency testing. The possibilities for experts to report on activity-related issues will increase as our knowledge increases through further research, access to relevant data is enhanced, and tools to assist interpretations are better exploited. Improvement opportunities will be achieved sooner, if more laboratories and agencies accept the need to invest in these aspects as well as the training of practitioners.
... Despite increased attention, and due to the development of more and more sensitive DNA analysis, alternative scenarios are always represented, involving DNA transfer through a secondary person or medium. The minute amount of a few cells or DNA molecules, which may be applicable for amplification, is not recognizable typically in an autopsy environment and is easily transferable between cases [4,117,118]. Although methodological developments are continuously making efforts to eliminate the effect of contamination artifacts from the profiling process [119,120], less appropriate autopsy sampling, incorporating the undetected contamination incidents, can lead to false interpretation within a DNA laboratory [5]. ...
Article
Several studies have demonstrated that DNA can be indirectly transferred from an individual onto a surface. Therefore, the presence of DNA that is compatible with a given person does not necessarily mean that this person has touched the surface on which the DNA was recovered. The present work simulates cases, where DNA is recovered on a door handle and compared to several reference DNA profiles. The DNA profile of the trace shares DNA components with a person of interest (POI). When asked about the DNA results, the POI says he has nothing to do with the incident and has never been at the scene. However, a possibility would be that the DNA came from his recently stolen gloves. Someone else, the alternative offender (AO), could have opened the door wearing his gloves (POI’s gloves), and transferred his DNA (POI’s DNA). Based on the above-mentioned scenario, 60 burglary simulations experiments were carried out to generate data to assess DNA results given these allegations. The quantity and quality of DNA profiles (NGM SElect) recovered when the POI opened/closed the door bare-handed or when someone else performed the same activity but using POI’s gloves, were compared. The gloves were regularly worn during at least three months by their owner during the winter. On the contrary, the AO wore them only for two minutes. Among the traces collected on the door handles, less than 50% of the traces led to interpretable DNA profiles. In 30% of the cases (3/10), when the door was opened/closed with bare hands, the DNA found on the door handle led to a mixed DNA profile with the POI’s DNA aligning with the major contributor. For the experiments where the AO opened/closed the door with the POI’s gloves, the POI’s DNA was compatible with 22% (11/50) of the mixed DNA profile, aligning with the major in 8% of the cases (4/50). The DNA profiles of the offices’ occupants were observed on the door handles, but not the AO’s. In addition to the results of the experiments, we show two examples of how one can assess results observed in casework. Given the possibility of indirect transfer of minute DNA quantities, this research emphasizes the need to evaluate DNA results given the activities when the POI has a legitimate reason that can explain the presence of their DNA.
Article
In the context of forensic evidence, the analysis of DNA traces often yields clear results, leading to a person as a potential source of the DNA. Statistical calculations support the hypothesis that the person in question was the source of (in the presence of a single profile) or a contributor to the trace (in the presence of a mixed DNA profile). In court DNA evidence itself is rarely ever questioned by the defence at source/sub-source level. More often, though, there is doubt about the ability of an incriminatory DNA match to positively identify the defendant as the perpetrator of the crime. Instead, the discussion shifts to the question of how the DNA of the defendant has been deposited on the evidence and thus switches to the so-called activity level. It is stated that the DNA of the defendant could have been transferred indirectly onto the evidence by another person or via an object (secondary transfer). As a consequence, the defendant would not have been involved in the offence. The possibility of such secondary or even tertiary transfer events (via another person or object) has been shown experimentally; however, indirect transfer of DNA traces (secondary or tertiary) is much less frequently observed than direct transfer (primary transfer). These recommendations discuss factors that support or question the assumption of an indirect transfer of DNA traces. Essential aspects for the interpretation of DNA results by forensic experts include the quantity of DNA of the person of interest detected in the trace as well as the existence and intensity of DNA deriving from other contributors and also the number of traces detected with the DNA profile of the person of interest.
Article
Current forensic DNA profiling kits and techniques enable the detection of trace amounts of DNA. With advancements in kit sensitivity, there is an increased probability of detecting DNA from contamination. Research into DNA transfer within operational forensic laboratories provides insight into the possible mechanisms that may lead to exhibit contamination. To gain a greater understanding of the potential for evidence bags to act as DNA transfer vectors, the level of DNA accumulating on the exterior of evidence bags during the exhibit examination process was investigated. The exterior of 60 evidence bags were tapelifted before and after the examination of the exhibit inside of the bag resulting in 120 DNA profiles. These DNA profiles were compared to DNA profiles of staff working within the building and samples taken from the exhibit inside the bag. Common DNA profile contributors from each sample were also identified through STRmix™ mixture to mixture analysis. The average DNA quantity and number of profile contributors was higher in samples taken from the bag before exhibit examination than after examination. Fifty six percent of all samples taken identified a match between DNA recovered from the evidence bag and at least one staff member. On 11 bags, a common contributor was identified between the exhibit in the bag and the exhibit package post-examination. In one instance a DNA profile, matching that of a donor, on the exhibit bag before examination was also detected on a sample taken from the exhibit, raising the possibility of outer bag-to-exhibit DNA contamination. This study demonstrates that operational forensic laboratories must consider exhibit packages as a potential source of DNA contamination and evaluate their exhibit handling and storage procedures accordingly.
Article
Blunt force traumas by footwear can result in severe and even fatal head and upper body injuries. Oftentimes, footwear impressions are only partially available and evidential value is limited. DNA evidence on shoe soles could provide crucial evidence helping to solve crimes by linking target DNA to the activity of interest. Little is known about the persistence and detectability of biological material post such offences and the interplay of factors affecting the analytical success. In this study, we assessed the persistence of blood on shoe soles under varying parameters such as blood location, different sneakers, weather condition, gait, amount of blood, underground and step count. We applied an optimized DNA/RNA workflow adapted to micro-traces without constraints for the primary DNA pipeline. There is a high probability to link donor DNA to the shoe sole for up to 300-400 steps, regardless of the underground, blood location, and amount of blood. Depending on the sole material and the degree of abrasion of the sole, a longer blood persistence can be observed. Considering blood, 98.2% of the initial DNA amount (1 μl initial blood volume) was lost after 100 steps walked on sole areas that are in constant contact with the ground. Proportion of foreign DNA was marginal (avg. 4.4 alleles), minimizing the probability of unintentional DNA transfer in this context. RNA typing showed high specificity but lower sensitivity than presumptive tests used for body fluid identification (BFI). Luminol is essential for targeted sampling on shoe soles, as latent blood traces (>100-200 steps) provided sufficient biological material for DNA/RNA typing. The generated data help to address the activity of interest and evaluate probabilities about prevalence of target DNA important for casework implications and assessments on activity level.
Article
DNA evidence on shoes can play an important role in solving a variety of crimes. We investigated the transfer, persistence, prevalence and recovery of DNA (DNAtppr) on shoes (sneakers) and their soles in realistic handling scenarios taking into account the shedder status. This study aims to increase the understanding of the expected composition of DNA profiles and their probative value, providing a basis for activity level assessments. Samples were analyzed using a direct lysis method, suggesting its versatility and increasing the DNA typing success compared to previous studies on footwear. The data show surface-dependent background DNA (bDNA) levels on shoe soles and prevalence of bDNA on the upper parts of the shoe. The owner of the shoe is allocatable to the mixture for almost every shoe and sampling location. Alternating scenarios of shoe handling were simulated through different pairs of shedders to distinguish shoe owner and subsequent user. Secondary users were attributable to DNA mixtures regardless of shedder status after wearing shoes a single time. The influence of the shedder status follows specific trends in this context. However, particularly intermediate shedders show inconsistent results. The prevalence of bDNA appears to have a greater effect on the impact of the shedder status on DNA profile composition than previously reported. The data help researchers to better resolve suspect statements and determine if a person of interest wore the shoes relevant to the investigation.
Article
DNA is frequently retrieved from commonly used objects or surfaces with no apparent biological stains. This DNA may have come from one or more individuals who directly deposited their DNA, or indirectly transferred the DNA of others, when physically contacting the sampled object or surface. Furthermore, contactless indirect DNA transfer of this ‘touch DNA’ from fabric substrates was recently demonstrated to be possible in a controlled laboratory environment. The circumstances and extent to which this form of contactless DNA transfer occurs are largely unknown. This study investigated indirect DNA transfer without contact by applying a gentle shaking agitation to used clothing, pillowcases and towels, with known usage and history, of 10 volunteers above the collection zone of the secondary surface. DNA transfer frequently occurred and was possible from all three investigated items. It occurred at levels that often produced informative profiles where transferred profiles closely resembled the profiles generated from the primary item. The outcomes of this study contribute to expanding the understanding of indirect DNA transfer without contact. However, this field would benefit from investigating a wider range of agitations and/or item types with various histories of use to determine the level of transfer and its detectability under different conditions.
Chapter
Matching a questioned fingermark from a crime scene with a suspect is one of the ways of achieving human identifications. However, if a fingermark is partial, distorted, or blurry beyond recognition, this task becomes more challenging, and sometimes cannot be attained solely based on fingermark ridge patterns. As a result, an alternative human identification approach will be necessary. Latent fingermarks are one of the sources of what has been named “touch DNA”, DNA left as a result of touching objects. Thus, DNA recovered from a fingermark can be used as another source of identification to confirm the results of a fingermark comparison and vice versa. There have been several studies that have focused on “touch DNA”/fingermark DNA in recent years. Some of these experiments investigated the source of this DNA and the factors that could affect its recovery, such as shedder status, environmental conditions, and time since deposition. Other studies concentrated on improving the techniques of DNA recovery and amplification along with other works that analyzed the potential interference of fingermark enhancement methodologies on DNA retrieval. This chapter presents an overview of the state-of-the-art technologies on DNA recovery, amplification, and profiling from “touch DNA”/fingermark DNA.
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Successful forensic DNA profiling from handled items is increasingly routine in casework. This “touch DNA” is thought to contain both cellular and acellular nucleic acid sources. However, there is little clarity on the origins or characteristics of this material. The cellular component consists of anucleate, terminally differentiated corneocytes (assumed to lack DNA) and the occasional nucleated cell. The acellular DNA source is fragmentary, presumably cell breakdown products. This study examines the relative contributions each component makes to the hand‐secretions (endogenous) and hand‐accumulations (exogenous) by recovering rinses from the inside and outside of worn gloves. Additionally, cellular and acellular DNA was measured at timepoints up to 2 h after hand washing, both with and without interim contact. Microscopic examination confirmed cell morphology and presence of nucleic acids. Following the novel application of a hair keratinocyte lysis method and plasma‐DNA fragment purification to hand rinse samples, DNA profiles were generated from both fractions. Exogenous cell‐free DNA is shown to be a significant source of touch DNA, which reaccumulates quickly, although its amplifiable nuclear alleles are limited. Endogenous DNA is mostly cellular in origin and provides more allelic information consistently over time. This article is protected by copyright. All rights reserved
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Bayesian logistic regression is used to model the probability of DNA recovery following direct and secondary transfer and persistence over a 24 h period between deposition and sample collection. Sub-source level likelihood ratios provided the raw data for activity-level analysis. Probabilities of secondary transfer are typically low, and there are challenges with small data-sets with low numbers of positive observations. However, the persistence of DNA over time can be modelled by a single logistic regression for both direct and secondary transfer, except that the time since deposition must be compensated by an offset value for the latter. This simplifies the analysis. Probabilities are used to inform an activity-level Bayesian Network that takes account of alternative propositions e.g. time of assault and time of social activities. The model is extended in order to take account of multiple contacts between person of interest and ’victim’. Variables taken into account include probabilities of direct and secondary transfer, along with background DNA from unknown individuals. The logistic regression analysis is Bayesian - for each analysis, 4000 separate simulations were carried out. Quantile assignments enable calculation of a plausible range of probabilities and sensitivity analysis is used to describe the corresponding variation of LRs that occur when modelled by the Bayesian network. It is noted that there is need for consistent experimental design, and analysis, to facilitate inter-laboratory comparisons. Appropriate recommendations are made. The open-source program written in R-code ALTRaP (Activity Level, Transfer, Recovery and Persistence) enables analysis of complex multiple transfer propositions that are commonplace in cases-work e.g. between those who cohabit. A number of case examples are provided. ALTRaP can be used to replicate the results and can easily be modified to incorporate different sets of data and variables.
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DNA transfer is a well-recognised phenomenon impacting the probability of detecting the presence of a particular source of DNA and thus the likelihood of the evidence given considered events within forensic investigations. Comprehensive study is lacking on variables associated with indirect DNA transfer without physical contact. Additionally, the drying properties of forensically relevant biological materials are under researched despite the recognised potential for these properties to affect DNA transfer. This study investigated the drying properties and indirect DNA transfer of dried blood, saliva, semen, vaginal fluid and touch DNA without contact deposited on two different non-porous hard substrates (melamine and glass) and two different porous soft substrates (polyester and cotton) by tapping (all substrates) and stretching (only fabric substrates) agitations. Different apparent drying trends were observed between the volumes, substrates and biological materials tested with substrate type generally having a greater influence than biological material. The rate and percentage of indirect transfer appeared to be dependent on agitation, substrate type, biological material and its drying properties. The outcomes of this study may assist those evaluating the likelihood of the evidence given proposed events during activity level assessments.
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DNA deposited by individuals’ hands is a routine part of forensic analysis, yet little is understood about the precise cellular contents left by handling. “Dead” skin cells known as corneocytes make up the majority of the cellular material left in touch deposits by people’s hands but are known to lack nuclei, making their DNA content ambiguous. Here we measure DNA released from anucleate corneocytes following various lysis methods to determine how much DNA may be present in these cells and how best to recover it from inside the cornified envelope. We demonstrate that enhanced lysis methods using a reducing agent and longer incubation may be valuable for hand deposit samples. Corneocyte DNA can be characterized as highly degraded based on the quantification, STR profiling and fluorescence microscopy of the cells from freshly washed hands. Purification to target shorter DNA fragments is demonstrated. DNA from the washed corneocyte cells is shown to constitute the majority of recoverable DNA with these methods. We consider the use of new methods adapted to cornified cells and fragmented DNA for future research into this sample type
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Although touch deposit DNA is widely used in forensic casework, its cellular and acellular contents and their biological origins are poorly understood. There is evidence that the cell-free component of DNA deposited by handling may contribute substantial genetic information; however, most research into touch DNA recovery does not separate cellular and cell-free fractions or seek to characterize their contents. This work is an important early step in developing methods to isolate the cfDNA from biological material deposited by handling. Size-filtration as a separation technique was determined to be prone to DNA loss, even on optimized control samples of pure ladder DNA. Centrifugal separation was optimized to determine minimum speed and time required to reliably remove all cellular debris from the material collected by rinsing donor hands. To determine if the centrifugal force risked rupturing shed corneocyte cells and releasing cellular DNA into the supernatant, DNA levels were measured, and cells were visualized microscopically before and after centrifugation of hand rinses. Heated buccal cells were used as a positive control to demonstrate cell rupture would be detected with these methods. Following the determination of a suitable separation technique, an investigation into purification methods for cfDNA was conducted. DNA recovery using three kits for plasma cfDNA, one for PCR clean-up and one for genomic DNA were assessed on both ladder DNA to simulate cfDNA fragments and on collected hand deposit supernatants from both unwashed and washed hands. Purification methods designed for recovery of short DNA fragments from plasma yielded the highest recovery percentage across sample types, with BioChain cfPure performing the best. Donors’ hands were shown to shed high levels of cfDNA, which were better recovered with a method for short fragments than with a traditional genomic technique often used on touch DNA samples.
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Forensic DNA typing from touched or handled items in routine casework is increasing as the sensitivity of detection techniques improves. Our understanding of the cellular/acellular content of touch deposits and the origins of the DNA therein is still limited. This work explores the cellular content of rinses from washed and unwashed hands, as well as saliva, nasal and eye washes which could be sources of transferred DNA onto hands. Flow cytometry and microscopic examination were used to detect granularity, size and nucleic acid fluorescence data. Cellular content did not vary significantly within an individual, although some differences were observed between donors. Saliva contained populations of nucleated epithelia as well as smaller cells and debris, all positive for DNA. Hand rinses consisted almost entirely of anucleate corneocytes, many of which also stained positive for nucleic acids. These data raise questions about shed corneocyte DNA content previously assumed to be negligible.
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The persistence of DNA on washed items as well as the DNA transfer has become a major subject of research in recent years, especially after the detectability of minor DNA traces was heavily increased by sensitive analysis methods. Nowadays, the attribution of a DNA trace to an individual is only rarely questioned, whereas the way of application of this DNA to an item is subject to much discussion and speculation. Additionally, the removal of DNA by cleaning or its possible persistence on an item despite a cleaning process are often important problems in court. The aim of this study was to investigate whether DNA traces (blood, saliva, epithelial cells) on different objects (knives, plates, glasses, and plastic lids) can persist on the surface despite cleaning by different methods like hand-washing or the use of a dishwasher. In total, 120 samples were collected from artificially constructed blood, saliva, and epithelial cell stains on objects with smooth surfaces after washing and analyzed by STR amplification. Samples taken after rinsing or hand-washing resulted mainly in complete DNA profiles (62.5% of samples), while cleaning in the dishwasher rendered almost everything completely DNA-free. Since in the hand-washing experiments a secondary transfer of DNA through the water could not be ruled out, additional transfer experiments were conducted with blood and saliva samples on plates. Here, a carryover of DNA traces could be demonstrated up to the fifth washed item.
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The use in courtrooms of forensic DNA typing results from presumably touched or handled items is increasing as the sensitivity of detection techniques improves. Research investigating how much DNA can be recovered from handled items, whether trace DNA can be detected under certain scenarios including varying degrees of indirect transfer, and factors which may influence these results is summarized here. Fundamentally, our current understanding of the cellular content of touch deposits and the origins of the potential trace DNA therein is extremely limited. Possible origins include anucleate corneocytes, fragmentary cells/nuclei, nucleated epithelial cells from hands, transferred nucleated cells, and cell-free DNA. Here we review the existing evidence for each possible source and consider remaining knowledge gaps regarding forensically relevant touch depositions.
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The detection of DNA of a certain person on the inside of a piece of clothing involved in a crime scene is usually seen as confirmation that this person is the owner or bearer and therefore participated in this crime. However, besides the possibilities of secondary or even tertiary transfer of DNA, the accused often argues that he lent the garment to another person who by chance did not leave any DNA while committing the crime. Then, forensic genetic scientists have to answer the question how long DNA persists on an item used in daily routine and how long a piece of clothing must be worn to definitively leave detectable DNA behind. In an attempt to answer these questions, several scenarios with two or three individuals wearing the same sweatband for different time periods were set up. DNA left on the sweatbands was isolated, quantified, and then analyzed using the Powerplex® ESX17fast kit. The majority of samples displayed all alleles of both/all three wearers on the outside (67%) as well as on the inside (80%) of the sweatbands. In contrast, a single profile of the first wearer could only be found once among all 204 samples, a single profile of the second wearer in 7% of samples. Wearing the sweatband for only 10 min was enough to result in a complete profile of the second wearer in 79% of samples. So, it is highly unlikely to wear/use a piece of clothing for even a short period of time without leaving own DNA behind.
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DNA traces on clothes of drowned bodies can provide important evidence for police investigations, especially in cases of suspected suicides or homicides. However, it is generally assumed that the water “erodes” a large part of the DNA depending especially on the exposure time. In forensic casework, DNA of suspects could be found frequently on clothes of drowned bodies after hours, sometimes days of exposure to water. This study was conducted to attempt a general statement about the conditions under which sufficient DNA remains can be expected for molecular genetic analysis. For this purpose, different scenarios were designed including DNA from three to five people, different types of waters (tap, pond, bathtub and river) for various time periods, with higher water pressure, different temperature, and soapy water (bathtub). Epithelial cells and blood cells were mounted on cotton cloths, and the DNA left after exposure was analyzed using the Powerplex® ESX17fast kit. In the indoor experiments, complete profiles could be seen even after 10 min rinsing of clothes under the tap and after 1 week in the bathtub. Outdoors, the results differed considerably between summer and winter as well as between pond and river. The longest exposure time still resulting in a complete profile was 2 weeks for a sample with skin cells in the pond during winter. In summer, the time period for erasing the bulk of DNA was 4 hours regarding epithelial samples and more than 1 day for blood samples in pond and river environments. All in all, the results demonstrate that DNA could still be recovered from clothes exposed to water for more than 1 week.
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In court questions are often raised related to how trace DNA was deposited, directly during the crime or innocently for instance by secondary transfer. It is therefore of interest to have knowledge of the probability of transfer or secondary transfer in different situations. Factors that could influence transfer probabilities are background DNA and the shedder status of the involved persons. In this study, we have classified participants as high or low DNA shedders. We observed DNAtransfer in a simulated attack scenario, and demonstrated that shedder status has a significant influence of transfer rates. We have examined the background DNA in samples from T-shirts worn in an area with frequent human traffic and detected multiple contributors. We further demonstratedthat DNA from co-workers of a T-shirt wearer can be secondarily transferred from the environment and detected in samples, and that the composition of background DNA is correlated with the shedder status of the wearer. Finally, we have illustrated the inference with the resultsof transfer probabilities and a fictive case with the use of a Bayesian network.
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Fingerprints can be of tremendous value for forensic biology, since they can be collected from a wide variety of evident types, such as handles of weapons, tools collected in criminal cases, and objects with no apparent staining. DNA obtained from fingerprints varies greatly in quality and quantity, which ultimately affects the quality of the resulting STR profiles. Additional difficulties can arise when fingerprint samples show mixed STR profiles due to the handling of multiple persons. After applying a tested protocol for sample collection (swabbing with 5% Triton X-100), DNA extraction (using an enzyme that works at elevated temperatures), and PCR amplification (AmpFlSTR® Identifiler® using 31 cycles) extensive analysis was performed to better understand the challenges inherent to fingerprint samples, with the ultimate goal of developing valuable profiles (≥ 50% complete). The impact of time on deposited fingerprints was investigated, revealing that while the quality of profiles deteriorated, full STR profiles could still be obtained from samples after 40 days of storage at room temperature. By comparing the STR profiles from fingerprints of the dominant versus the non-dominant hand, we found a slightly better quality from the non-dominant hand, which was not always significant. Substrates seem to have greater effects on fingerprints. Tests on glass, plastic, paper and metal (US Quarter dollar, made of Cu and Ni), common substrates in offices and homes, showed best results for glass, followed by plastic and paper, while almost no profiles were obtained from a Quarter dollar. Important for forensic casework, we also assessed three-person mixtures of touched fingerprint samples. Unlike routinely used approaches for sampling evidence, the surface of an object (bottle) was sectioned into six equal parts and separate samples were taken from each section. The samples were processed separately for DNA extraction and STR amplification. The results included a few single source profiles and distinguishable two person mixtures. On average, this approach led to two profiles ≥ 50% complete per touched object. Some STR profiles were obtained more than once thereby increasing the confidence.
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To improve and advance DNA forensic casework investigation outcomes, extensive field and laboratory experiments are carried out in a broad range of relevant branches, such as touch and trace DNA, secondary DNA transfer and contamination confinement. Moreover, the development of new forensic tools, for example new sampling appliances, by commercial companies requires ongoing validation and assessment by forensic scientists. A frequent challenge in these kinds of experiments and validations is the lack of a stable, reproducible and flexible biological reference material. As a possible solution, we present here a cell culture model based on skin-derived human dermal fibroblasts. Cultured cells were harvested, quantified and dried on glass slides. These slides were used in adhesive tape-lifting experiments and tests of DNA crossover confinement by UV irradiation. The use of this model enabled a simple and concise comparison between four adhesive tapes, as well as a straightforward demonstration of the effect of UV irradiation intensities on DNA quantity and degradation. In conclusion, we believe this model has great potential to serve as an efficient research tool in forensic biology.
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DNA quantification is an important step in the molecular genetic analysis of a forensic sample, hopefully providing reliable data on DNA content for a subsequent generation of reproducible STR profiles for identification. For several years, this quantification has usually been done by real-time PCR protocols and meanwhile a variety of assays are commercially available from different companies. The newest one is the PowerQuant(TM) assay by Promega Inc. which is advertised with the promise that a determined DNA concentration of 0 ng/μl in a forensic sample guarantees the impossibility to achieve true STR results, thus allowing to exclude such samples from STR analysis to save time and money. Thus, the goal of this study was to thoroughly verify the quantification step with regard to its suitability as a screening method. We have evaluated the precision and reliability of four different real-time PCR quantification assays by systematically testing DNA dilutions and forensic samples with various DNA contents. Subsequently, each sample was subjected to the Powerplex® ESX 17 fast kit to determine a reliable cutoff level for exclusion of definitely negative samples from STR analysis. An accurate quantification of different cell line DNA dilutions was not possible with any kit. However, at least the PowerQuant(TM) assay provided suitable data analyzing forensic samples, whereas in other systems up to 46 % of negative samples still displayed reliable STR analysis results. All in all, the PowerQuant(TM) assay represents a big step forward, but the evaluation of real-time PCR quantification results has still to be done with great care.
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DNA analysis is frequently used to acquire information from biological material to aid enquiries associated with criminal offences, disaster victim identification and missing persons investigations. As the relevance and value of DNA profiling to forensic investigations has increased, so too has the desire to generate this information from smaller amounts of DNA. Trace DNA samples may be defined as any sample which falls below recommended thresholds at any stage of the analysis, from sample detection through to profile interpretation, and can not be defined by a precise picogram amount. Here we review aspects associated with the collection, DNA extraction, amplification, profiling and interpretation of trace DNA samples. Contamination and transfer issues are also briefly discussed within the context of trace DNA analysis. Whilst several methodological changes have facilitated profiling from trace samples in recent years it is also clear that many opportunities exist for further improvements.
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This research investigates factors that may influence the secondary transfer of DNA. These include the type of biological substance deposited, the nature of the primary and secondary substrate, moisture content of the deposit and type of contact between the surfaces. Results showed that secondary transfer is significantly affected by both the type of primary substrate and the moisture (wetness) of the biological sample. Porous substrates and/or dry samples diminished transfer (with on average only 0.36% of biological material being transferred from one site to another), whereas non-porous substrates and/or wet samples facilitated transfer events (approximately 50-95% of biological material was transferred from one site to another). Further, the type of secondary substrate also influenced transfer rate, with porous surfaces, absorbing transferred biological substances more readily than non-porous ones. No significant differences were observed among the biological substances tested (pure DNA, blood and saliva). Friction contact between the two substrates significantly enhanced secondary transfer compared to either passive or pressure contact. These preliminary results will assist in developing general assumptions when estimating probability of a secondary DNA transfer event under simple conditions.
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In the course of forensic DNA analysis, the interpretation of DNA profiles of mixed stains, i.e. cell material from more than a single donor, has become increasingly more important. The German Stain Commission, a joint commission of Institutes of Forensic Science and Legal Medicine, has therefore developed guidelines aiming to harmonize the evaluation of mixed stains in German criminal cases.
Article
Forensic genetic analysis of items possibly handled by a suspect or a victim is frequently inquired by the law enforcement authorities, since DNA left on touched objects can often be linked to an individual. Due to technical improvement, even poor traces, which seemed to be unsuitable for DNA analysis a few years ago, may be amplified successfully today. Yet, DNA can be transferred to a crime scene artificially or unintentionally without any primary contact between the individual and the object found at the crime scene, the so-called secondary transfer or indirect transfer in general. In this study, "secondary transfer" scenarios with cells and DNA of different origins under wet conditions were investigated. Transfer was simulated as either "washing by hand" in a washtub or as "machine laundry" in a washing machine. As expected, major differences were seen between blood stains and epithelial abrasions. DNA from blood donors could be detected clearly both on the donor and on the acceptor textile, regardless of washing method. Regarding epithelial abrasions, simulating worn clothes, after washing by hand, only little residual DNA was found, and partial profiles were displayed on the donor textile, while transfer to the acceptor textile occurred even less and not in noteworthy amount and quality. Single alleles could be found both on donor textiles and acceptor textiles after simulated machine wash, but no reliable DNA profile could be verified after laundry in machine. Therefore, a DNA transfer from one worn cloth (without blood stains) to another textile in the washing machine seems to be extremely unlikely.
Article
With the introduction of new multiplex PCR kits and instrumentation such as the Applied Biosystems 3500xl, there has recently been a rapid change in technology that has greatly increased sensitivity of detection so that a DNA profile can routinely be obtained from only a few cells. Research to evaluate the risks of passive transfer has not kept pace with this development; hence the risk of innocent DNA transfer at the crime-scene is currently not properly understood. The purpose of this study was to investigate the possibility of investigator-mediated transfer of DNA traces with disposable nitrile-gloves used during crime-scene examinations. We investigated the primary transfer of freshly deposited DNA from touched plastic, wood or metal substrates and secondary and tertiary transfer by a person wearing disposable nitrile-gloves and onto a third object. We show that with use of the new highly sensitive technologies available in forensic DNA analysis there is an enhanced probability to obtain a DNA-profile which has not been directly deposited on the object but is an outcome of one or more transfer events. The nitrile-gloves used by investigators during exhibit examination can act as a vector for DNA transfer from one item to another. We have shown that the amount of DNA deposited on an object affects the probability of transfer. Secondly, the type of substrate material that DNA is deposited onto has an impact on transfer rates. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.
Article
When questions relating to how a touch DNA sample from a specific individual got to where it was sampled from, one has limited data available to provide an assessment on the likelihood of specific transfer events within a proposed scenario. This data is mainly related to the impact of some key variables affecting transfer that are derived from structured experiments. Here we consider the effects of unstructured social interactions on the transfer of touch DNA. Unscripted social exchanges of three individuals having a drink together while sitting at a table were video recorded and DNA samples were collected and profiled from all relevant items touched during each sitting. Attempts were made to analyze when and how DNA was transferred from one object to another. The analyses demonstrate that simple minor everyday interactions involving only a few items in some instances lead to detectable DNA being transferred among individuals and objects without them having contacted each other through secondary and further transfer. Transfer was also observed to be bi-directional. Furthermore, DNA of unknown source on hands or objects can be transferred and interfere with the interpretation of profiles generated from targeted touched surfaces. This study provides further insight into the transfer of DNA that may be useful when considering the likelihood of alternate scenarios of how a DNA sample got to where it was found.
Article
In crime scene investigations, DNA left by touch on an object can be found frequently and the significant improvements in short tandem repeat (STR) amplification in recent years built up a high expectation to identify the individual(s) who touched the object by their DNA profile. Nevertheless, the percentage of reliably analysable samples varies considerably between different crime scenes even if the nature of the stains appears to be very similar. Here, it has been proposed that the amount and quality of DNA left at a crime scene may be influenced by external factors (like nature of the surface) and/or individual factors (like skin conditions). In this study, the influence of the age of an individual who left his DNA on an object is investigated. Handprints from 213 individuals (1 to 89 years old) left on a plastic syringe were analysed for DNA amount and STR alleles using Quantifiler® and PowerPlex® ESX 17. A full profile of the individual could be found in 75 % of all children up to 10 years, 9 % of adolescents (11 to 20 years), 25 % of adults (21 to 60 years) and 8 % of elderly people (older than 60 years). No person older than 80 years displayed a full profile. Drop-in and drop-out artefacts occurred frequently throughout the age groups. A dependency of quantity and quality of the DNA left on a touched object on the age of the individual could be clearly demonstrated at least for children and elderly people. An epithelial abrasion unexpectedly good to interpret may be derived from a child, whereas the suspected skin contact of an elderly person with an object may be impossible to prove.
Article
DNA-bearing cellular material can come to be present on a surface by either direct or indirect transfer. Direct transfer includes contact, but also includes activities within the vicinity of an item that may result in the transfer of DNA directly from an individual without any contact, such as speaking, coughing, and sneezing. Indirect transfer of DNA is when DNA from an individual comes to be on an item via an intermediary surface. It is important to consider indirect transfer in the evaluation of trace DNA in casework. The term 'trace DNA' in this review refers solely to DNA that cannot be attributed to an identifiable body fluid. This review presents and considers data from trace DNA experiments to establish whether the quantity of DNA recovered from a crime stain and/or the quality of a DNA profile obtained can be used to infer the likely mechanism of transfer. The data show that varied results are obtained from apparently similar trace DNA samples, presumably due to the many factors that affect the detection of trace DNA. The nature and effect of these varying factors and the application of the data to casework is considered generally and with specific reference to DNA transfer to skin, DNA beneath fingernails, 'wearer DNA', and various contamination considerations.
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The circumstances surrounding deposition of DNA profiles are increasingly becoming an issue in court proceedings, especially whether or not the deposit was made by primary transfer. In order to improve the currently problematic evaluation of transfer scenarios in court proceedings, we examined the influence a variety of nine substrate types (six varieties of fabric, plywood, tarpaulin, and plastic sheets) has on DNA transfer involving blood. DNA transfer percentages were significantly higher (p = 0.03) when the primary substrate was of non-porous material (such as tarpaulin, plastic or, to a lesser degree, wood) and the secondary substrate porous (such as fabrics). These findings on transfer percentages confirm the results of previous studies. Fabric composition was also shown to have a significant (p = 0.03) effect on DNA transfer; when experiments were performed with friction from a variety of fabrics to a specific weave of cotton, transfer percentages ranged from 4% (flannelette) to 94% (acetate).
Article
DNA transfer and its possible role in explaining the presence of a biological sample at a crime scene is becoming more prevalent in criminal investigations and related court proceedings. To assist understanding of DNA transfer and assess the extent to which we can utilise already available information regarding transfer of DNA we compare transfer rates determined from mock multi-step transfer scenarios with transfer rates predicted by the application of currently available transfer rate data. The transfer results obtained from the scenarios tested were, in some instances, different (both lower and higher rates) from those predicted. These discrepancies are most likely the result of the impact of as yet untested variables. These may include the variations in substrate type, transfer area size and environmental factors such as temperature and humidity among others. Whilst detailed re-enactments of proposed transfer scenarios, that take into account the many possibly relevant aspects affecting transfer are desirable, to provide an accurate likelihood estimate, these are not always possible. The application of detailed transfer rate tables that include data on the many factors affecting transfer could provide a useful substitute for evaluating the likelihood of specific transfer events. The value and accuracy derived from applying such tables will improve as more research in this area is conducted and the tables expanded and refined.
Article
DNA evidence frequently plays an important role in criminal investigations and in some cases may be the only means of convicting a suspect. The constant improvement of DNA analysis techniques affords the individualization of minute amounts of DNA, aggravating the risk of contamination artifacts. In our study, we investigated the prevalence of DNA contamination in the autopsy facilities of the Institutes of Legal Medicine in Essen and Kiel (Germany). Using DNA-free swabs, we took samples from instruments used during autopsy and autopsy tables. Surfaces and instruments were routinely cleaned before sampling. Swabs were subjected to different PCRs to quantify the total amount of DNA and to amplify individual specific STR-markers. In most samples, alleles that could be linked to bodies that had been autopsied before were found. Furthermore, we could show that a DNA transfer from the autopsy table to a body was detectable in four out of six cases investigated. The interpretation of DNA typing results may thus be severely complicated. To avoid DNA contamination, we tried out different cleaning methods, of which only a bleach containing cleaner showed sufficient results.
Article
The successful analysis of weak biological stains by means of highly sensitive short tandem repeat (STR) amplification has been increased significantly over the recent years. Nevertheless, the percentage of reliably analysable samples varies considerably between different crime scene investigations even if the nature of the stains appears to be the same. It has been proposed that the amount and quality of DNA left at a crime scene may be due to individual skin conditions (among other factors). Therefore, we investigated DNA from handprints from 30 patients acutely suffering from skin diseases like atopic dermatitis, psoriasis or skin ulcer before and after therapy by STR amplification using the new and highly sensitive Powerplex® ESX17 kit in comparison to 22 healthy controls. Handprints from atopic dermatitis patients showed a correct and reliable DNA profile in 90% and 40% of patients before and after therapy, respectively. Regarding psoriasis patients, we detected full DNA profiles in only 64% and 55% of handprints before and after therapy. In contrast, in ulcus patients and controls, full DNA profiles were obtained in much lower numbers. We conclude that active skin diseases like atopic dermatitis or psoriasis have a considerable impact on the amplificable DNA left by skin contact with surfaces. Since up to 7% of adults in European countries suffer from one of these diseases, this could explain at least partially the varying quality of DNA from weak stains.
Article
The transfer of DNA from hands to objects by holding or touching has been examined in the past. The main purpose of this study was to examine the variation in the amount of DNA transferred from hands to glass, fabric and wood. The study involved 300 volunteers (100 for glass, 100 for fabric and 100 for wood) 50% of which were male and 50% female. The volunteers held the material for 60s. The DNA was recovered from the objects using a minitape lift, quantified using the Quantifiler kit assay, extracted using a 'Qiagen(®) QIAamp DNA mini kit' and amplified using the AmpFlSTR(®) SGM Plus™ Amplification Kit at 28 cycles. The results show that using ANOVA there was a significant difference (F=8.2, p<0.05) between the three object types in the amount of DNA recovered. In terms of DNA transfer and recovery, wood gave the best yield, followed by fabric and then glass. The likelihood of success of obtaining a profile indicative of the holder was approximately 9% for glass samples, 23% for fabric and 36% for wood. There was no significant difference between the amount of DNA transferred by male or female volunteers. In this study good shedder status, as defined by obtaining useful profiles of 6 or more alleles, is estimated at approximately 22% of the population. The phenomenon of secondary transfer was observed when mixed DNA profiles were obtained but the incidence was low at approximately 10% of the total number of samples. DNA profiles corresponding to more than one person were found on objects which had been touched by only one volunteer. Although secondary transfer is possible the profiles obtained from touched objects are more likely to be as a result of primary transfer rather than a secondary source.
Article
In the past, it was almost impossible for forensic scientists to separate DNA from an undefined number of different individuals in mixed stains where, for example, two or more suspects had handled the same weapon. Such samples often contain complex mixtures with the consequence of ambiguous or inconclusive mixed DNA profiles. Using the method described of comprehensive and/or targeted screening of shed cells adhering to tapings of garments or objects enables such stains to be individualized. To evaluate the method, 500 microscopically selected single skin flakes were analyzed using two different commercial STR kits to compare the success rates for each PCR typing system. The method has been validated for use in routine casework and has been shown to be rapid, sensitive, and reproducible. It can be predicted that many cases in the archives with body tapings, which have not yet been examined will benefit from this new or perhaps more appropriate, reanimated, technical development, and of particular importance are serious crimes, the so-called cold cases. The remarkable forensic value of this simple but time-consuming technique is exemplified by 2 out of approximately 100 cases already successfully solved using this approach.
Article
There is a paucity of data on the relative transfer rates of deposited biological substances which could assist evaluation of the probability of given crime scene scenarios, especially for those relating to objects originally touched by hand. This investigation examines factors that may influence the secondary transfer of DNA from this source, including the freshness of the deposit, the nature of the primary and secondary substrate and the manner of contact between the surfaces. The transfer rates showed that both the primary and secondary type of substrate and the manner of contact are important factors influencing transfer of skin cells, but, unlike other biological fluids, such as blood and saliva, the freshness of the deposit in most instances is not. Skin cells deposited on a non-porous primary substrate transferred more readily to subsequent substrates than those deposited on a porous substrate. Porous secondary substrates, however, facilitated transfer more readily than non-porous secondary substrates, from both porous and non-porous surfaces. Friction as the manner of contact significantly increased the rate of transfer. The findings of this study improve our general understanding of the transfer of DNA material contained in fingerprints that is left on a surface, and assist in the evaluation of the probability of secondary and further DNA transfer under specific conditions.
Article
Recent advances in molecular techniques have revolutionized our approaches and expanded our vistas in the biomedical and organismal sciences. The development of the Polymerase Chain Reaction (PCR) has been the major reason for this revolution. Nearly every field of biology now owes a great deal to the development of these molecular techniques. The historically oriented sciences are an area of biology that has especially benefitted from PCR technology. This is because deoxyribonucleic acids are molecules that can carry genealogical information. Its double helical complementary nature and method of replication make it a perfect storage receptacle for historical information, whether the history be ancient or recent. In particular, in the organismal sciences, large advances have been made in the fields of evolutionary biology, population biology and systematics.
Article
Forensic scientists regularly generate genetic profiles from old blood stains, seminal stains, vaginal swabs, hair, bone, urine and cigarette butts. We show that an individual's genetic profile can now also be generated from swabs taken from objects touched by hands, providing a new tool for crime scene investigations. Our findings also demonstrate the need for caution when handling exhibits and when interpreting results.
Article
Van Oorschot and Jones reported in Scientific Correspondence that short tandem repeat (STR) profiles (DNA fingerprints) can be obtained from cells left on pens, car keys, and so on. Although this technique is a dramatic breakthrough with important implications for forensic science, there are two main limitations. First, more than 1 ng DNA (equivalent to 200 cells) is required; and second, a single STR locus is used, which does not provide much information. Here we report a system for determining STR profiles from single cells using six forensic STR markers, which we believe is the first time that single cells have been typed using modern forensic techniques.
Article
With the continuing development of extremely sensitive, automated systems for the detection of human DNA from a number of cellular sources, the problem of sample contamination from scenes of crime, cadavers, and the mortuary environment has become a potentially serious issue, with implications for all involved in forensic investigations. A recent survey of 20 mortuaries identified quantifiable human DNA on mortuary work surfaces and instruments which, when amplified, produced in some cases three or more profiles from single site samples. Possible sources of DNA contamination in the mortuary are discussed, along with implications related to its presence and its avoidance during the sampling process. These observations may not be confined to forensic practice.
Article
Advances in STR PCR DNA profiling technology allow for the analysis of minute quantities of DNA. It is frequently possible to obtain successful DNA results from cellular material transferred from the skin of an individual who has simply touched an object. Handling objects, such as weapons or other items associated with a crime, touching surfaces, or wearing clothing, may represent sufficient contact to transfer small numbers of DNA bearing cells, or trace DNA, which can be successfully analyzed. With this minimal amount of contact required to yield a suspect profile comes tremendous crime solving potential, and a number of considerations for prudent application, and the maximization of evidentiary value. Evidentiary materials not previously considered must be recognized and preserved, and the resulting DNA type profiles interpreted in their proper forensic context.
Article
We have shown that there is a difference between individuals in their tendency to deposit DNA on an item when it is touched. While a good DNA shedder may leave behind a full DNA profile immediately after hand washing, poor DNA shedders may only do so when their hands have not been washed for a period of 6h. We have also demonstrated that transfer of DNA from one individual (A) to another (B) and subsequently to an object is possible under specific laboratory conditions using the AMPFISTR SGM Plus multiplex at both 28 and 34 PCR cycles. This is a form of secondary transfer. If a 30 min or 1h delay was introduced before contact of individual B with the object then at 34 cycles a mixture of profiles from both individuals was recovered. We have also determined that the quantity and quality of DNA profiles recovered is dependent upon the particular individuals involved in the transfer process. The findings reported here are preliminary and further investigations are underway in order to further add to understanding of the issues of DNA transfer and persistence.
Article
Traditionally, sperms are isolated from vaginal cell mixtures by preferential extraction methods. Although these methods work well when there is a reasonable amount of DNA present, they are problematic when there are limited amounts (ca. 250 pg). In particular, the analysis of sperm from microscope slides has proven difficult. Here, we describe the use of laser capture microdissection (LM) for the isolation of spermatozoa from microscope slides containing sperms and vaginal cells. Such slides are frequently an important source of evidential material during the forensic investigation of rape and other sexual assaults. Low copy number (LCN) PCR was used to compare profiles of sperm DNA prepared using LM and preferential lysis. LM was found to outperform preferential lysis in 15 out of 16 samples. The application of LM to the processing of actual casework slides, and in particular the potential use of LM for the analysis of old cases, is discussed. Finally, 77 post-coital slides were processed in order to accurately assess the robustness of the technique. There was a significant association between the quality of the male profile recovered and time since intercourse that was independent of the number of sperms analysed, suggesting that the DNA was degraded even though the spermhead was intact.
Article
Isolation and identification of single cells from tissue samples or smears assume a great relevance in pathological and forensic applications; in this latter field, the possibility to identify a specific genetic profile can be obtained by short tandem repeat (STR) typing, allowing to achieve a scientific proof important in law courts. It is well known that DNA extraction may be performed from several tissue fragments, blood traces, spermatozoa as well as telogen hair. However, in the last case, few follicle cells are coupled to a great amount of keratin reducing the efficiency of DNA amplification. Recently, the introduction of laser microdissection technique has greatly improved the capability to select single cells without any cross-contamination. In the present report, we have performed a laser microdissection using a Leica AS LMD (Leica Microsystems, Germany), utilized on cutting the telogen hair in order to exclusively collect the lower part of the follicle and reduce keratin contamination. In this way we can accurately extract an adequate amount of DNA, successfully typed by STR profile.
Article
This research investigates factors influencing the transfer of DNA to handled objects and the process known as 'shedding'. Volunteers were recruited to hold sterile plastic tubes using experiments originally designed by Lowe et al. [A. Lowe, C. Murray, J. Whitaker, G. Tully, P. Gill, The propensity of individuals to deposit DNA and secondary transfer of low level DNA from individuals to inert surfaces, Forensic Sci. Int. 129 (2002) 25-34]. Transferred cellular material was collected from the tubes and STR profiles generated using the AmpFlSTR SGM Plus multiplex with 28 and 34 PCR cycles. Volunteers were asked to hold the tubes with each hand, and to participate in a series of handwashing experiments. The DNA profiling results obtained from the transferred skin cells were compared. An attempt was made to characterize the volunteers as 'good' or 'bad' shedders and to establish which, if any, of the experimental variables were associated with 'good' shedding. Our results suggest that many factors significantly influence shedding, including which hand an individual touches an item with and the time that has elapsed since they last washed their hands. We have found that it may be more complicated than previously reported to categorise a person as being either a 'good' or a 'bad' shedder and that if truly 'good' shedders exist they may be significantly rarer than some have estimated. In the current research no 'good' shedders were observed in a group of 60 volunteers. Given these results, it seems that rather than being applied to individual forensic cases, knowledge of shedding characteristics will be most useful in providing general background data for the interpretation of trace DNA evidence.