Article

Individual human scent as a forensic identifier using mantrailing

Authors:
  • Hochschule der Sächsischen Polizei (FH)
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Abstract

Specially trained dogs have long been used by law enforcement agencies to help in criminal investigations and in searching for missing persons. Still, it is unclear which components of human scent released into the environment contribute to successful searches of individuals. In this study, saliva and axillary sweat samples were taken from a total of 190 people. Additionally, DNA was extracted from whole blood of seven different people and used as an odour sample as well. Overall 675 tests (trails) were performed during a period of 18 months. The ability to track individuals with the odour samples mentioned above was examined with seven dogs, four of which were specially-trained dogs (mantrailer) from the Saxony Police. Results indicated that specially-trained police dogs can track a person with an average success rate of 82% and correctly identify the absence of an odour track with an average success rate of 97% under various conditions. Private rescue dogs were less successful with an average success rate of 65% and 75% respectively. These data suggest that the potential error rate of a well-trained handler team is low and can be a useful tool for law enforcement personnel. Saliva, as a reference odour source, was found to be particularly suitable for the search. The results of the study suggest that the components contained in axillary sweat, saliva and DNA extracted from whole blood are sufficient, serving as a key stimulus for individualized searches.

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... The specifics of the olfactory information remain elusive. It has been recently conjectured that dogs might be able to trace through olfaction molecules of DNA 45 . However, this assumption has been called into question, since DNA pieces which are large enough for individual identification are too large to be sufficiently volatile to find their way into the nose of a sniffing dog 46,47 . ...
... However, this assumption has been called into question, since DNA pieces which are large enough for individual identification are too large to be sufficiently volatile to find their way into the nose of a sniffing dog 46,47 . But undoubtedly dogs and other animals are able to identify individuals by scent, although the exact process is not fully understood [45][46][47][48] . ...
... Moreover, it was criticized in the study of Woidtke et al. (2018) 45 that the trail was only 5 min old and the target person was present, so that the dogs could use air scenting. In the present study the time delay between laying the trail and searching was also rather short (15 min), and the target person was present-so that dogs could also use air scenting. ...
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... Dear Sir, with interest we have read the article "Individual human scent as a forensic identifier using mantrailing" [1] published in Forensic Science International wherein the ability of mantrailing dogs to track individuals from different odor samples was analyzed and quantified in three experimental series. Most notably, the authors state that in a fourth experimental series they isolated DNA from blood (n = 61) used it as an odor sample and claim to have shown that trained dogs can trail individuals with statistically significant success rates even from odor samples of isolated DNA. ...
... In conclusion, we argue that 1 It is highly improbable that DNA can act as volatile odor component, that can bind to scent receptors and that its nucleotide sequence can enable scent based individualization, 2 There is no scientifically sound evidence that dogs can smell DNA and thereby differentiate individuals and that the methods described in the study by Woidtke et al. [1] did not and were not suited to provide such evidence, 3 The authors' conclusion that "DNA samples provides (sic) enough information for the dog to search for an individual" is not supported by evidence, should not have been made and should be corrected. Their study should not be used to support such claims in court. ...
... The human scent and its molecular profile are one of the major topics of current forensic interest. The possibility of its chemical analysis and identification of the individual based on scent composition would mean a significant breakthrough in forensic practice, providing more convincing evidence than specially trained dogs [1][2][3][4][5]. In addition to forensic practice, monitoring changes in the molecular profile of an individual would be of great importance for the evaluation of physical or mental conditions in biometric and medical applications [6][7][8]. ...
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... For the reasons mentioned above, we decided in our previous study to collect axillary sweat [3], which is also a key odour for the search and rescue [62,63], and the axillary region is easily accessible. Furthermore, this site is unlikely to be contaminated by saliva of a COVID-19 positive patient. ...
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... With regard to the questions raised concerning our article [8], we have had a statistical verification carried out again. As a result, the given number of negative samples is the unlikely expression of a stochastic process that follows a uniform distribution. ...
... Axillary sweat samples were collected because it seems a promising substrate for canine detection [21,44], is the key odour for search and rescue or tracking dogs [45], and the axillary region is easily accessible (Fig 2). Furthermore, this site is unlikely to be contaminated by the saliva of a COVID-19 positive patient. ...
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The ability of dogs to determine the direction of a track has been subject to little study. We conducted two experiments to examine the ability of dogs to identify the direction of human-laid trails and explore the mechanisms by which dogs determine directionality. Experiment 1 investigated the influence of canine sex and age on the ability of 22 police dogs to determine the correct direction of 10 human-laid trails. The direction in which the trail was laid on the dogs' ability to determine directionality was also explored. Eight (36.3%) dogs were consistently able to determine the correct direction of the trails. Male dogs identified the correct direction of the trails more frequently than females. Younger dogs were better at identifying the correct direction of the trails than older animals. Dogs identified the correct direction of those trails laid from left to right more frequently than those laid from right to left. Experiment 2 explored whether dogs use olfactory or visual cues to determine the correct direction of a human-laid trail. Eight dogs that were capable of following human trails in the correct direction were employed to track 10 trails that had been laid by a handler walking backwards, thereby rendering the trails devoid of accurate directional visual information. All of the dogs were consistently able to identify the correct direction of the trails. Overall, findings suggest that relatively few of the dogs in this study were accurately able to track in the correct direction, and that the dogs' ability to determine directionality was related to the animals' age and sex. Findings also suggest that the dogs employed olfactory cues to correctly elucidate direction.
Article
Controlled experiments are described showing that Police dogs trained to follow human tracks, and show dogs trained to retrieve objects scented by people, can distinguish fairly reliably between the body odours of different individuals, including the members of a family. The individuality of a person's body odour as perceived by the dog's nose is not greatly dependent on the region (e.g. palm, armpit, sole) from which it emanates, although these regional odours appear quite different to the human nose. The individual odour of a person is perceived by the dog even when mixed with another person's body odour, or with some strongly smelling substances.In retrieving experiments the body odours of identical twin partners offered in succession are accepted for each other and there is no indication that the dogs perceive any difference.In tracking experiments in which two body odours are offered simultaneously and mixed up, those of identical twin partners are distinguished by the dogs. However, when the odour of one twin is offered in place of the odour of the partner, and in the latter's absence, it is picked out from the odours of other people. Thus, the odours of identical twin partners, although more similar than those of any other people tested, can nevertheless be distinguished by well trained dogs.
Article
Scent identification lineups using dogs are a potentially valuable forensic tool, but have been dismissed by some critics because of cases where a false identification was shown to have occurred. It is not known, however, why dogs appear to make more false indications to the odors of some persons than of others. In this study, human genders were compared as to the degree their individual odors are distinguishable or "attractive" to dogs. Six dogs were trained to smell an individual's hand odor sample and then find the matching hand odor sample in a lineup of five odors. Using one-gender lineups and two-gender lineups with different gender ratios, it was found that dogs trained for the study identified individual women's hand odors more accurately than those of men. It is hypothesized that this is either because of differences in chemical compounds making discrimination of women's odors easier, or because of greater "odor attractiveness" of women's scents to dogs.
Article
Human scent can be collected by either contact or non-contact sampling mode. The most frequently used human scent evidence collection device known as the Scent Transfer Unit (STU-100) is a dynamic sampling device and is often used in a non-contact mode. A customized human scent collection chamber was utilized in combination with controlled odor mimic permeation systems containing five standard human scent volatiles to optimize the flow rate, collection material and geometry of the absorbent material. The scent collection method which yielded the greatest amount of volatile organic compounds (VOCs) detected included the use of a single layer of Johnson and Johnson gauze/multiple layers of Dukal gauze with the STU-100 on the lowest flow rate setting. The correlation of the resulting VOC profiles demonstrate that collection of standard VOCs in controlled conditions yielded reproducible VOC profiles on all materials studied with the exception of polyester. Finally, the method was tested using actual human subjects under optimized set of conditions.
Article
In this study it is demonstrated that human odor collected from items recovered at a post-blast scene can be evaluated using human scent specific canine teams to locate and identify individuals who have been in contact with the improvised explosive device (IED) components and/or the delivery vehicle. The purpose of the experiments presented here was to document human scent survivability in both peroxide-based explosions as well as simulated roadside IEDs utilizing double-blind field trials. Human odor was collected from post-blast device and vehicle components. Human scent specific canine teams were then deployed at the blast scene and in locations removed from the blast scene to validate that human odor remains in sufficient quantities for reliable canine detection and identification. Human scent specific canines have shown the ability to identify individuals who have been in contact with IEDs using post-blast debris with an average success from site response of 82.2% verifying that this technology has great potential in criminal, investigative, and military applications.
Article
In reply to a suggestion made by Galton in 1875, the ability of dogs to discriminate between the odour of human twins was investigated. In a matching-to-sample simultaneous discrimination task, dogs were tested on their ability to discriminate odours from twins differing only in genetic relatedness or only in environmental factors, particularly diet, or from twins identical in both genetic relatedness and environmental factors. Dogs could discriminate between the odours from twins who differed only in environmental factors and between the odours of twins who differed only in genetic relatedness. However, they were unable to discriminate between odours produced by infant twins identical in both genetic relatedness and environmental factors. Thus twins may be discriminated by dogs as long as they differ in genetic relatedness or environmental factors. The possible source of discriminable odours is discussed and how the effects of genes and environment are mediated considered.
Article
The Dutch police use specially trained dogs, Canis familiaris, to identify criminals from scented objects left at the scene of the crime. As part of a study of the reliability of these identifications, experiments were performed to evaluate whether these dogs could match scents collected from different parts of the body. Dutch police dogs are capable of matching hand scent to scent collected in the crook of the elbow and vice versa, and of matching trouser pocket scent to hand scent. It appears that training and familiarity with the person whose scents have to be matched enhance the performance of the dogs. The reliability for judicial purposes entails further research since our knowledge of the sense of smell is limited.
Article
To properly evaluate different forensic techniques, it is important to know how reliable these different techniques are. The reliability of scent identification line-ups is unknown. The purpose of this study was to describe, and employ, a reliability testing method for scent identifications using trained police dogs and a novel scent identification procedure. Two kinds of experiments were prepared: suspect = perpetrator experiments, and suspect not equal to perpetrator experiments. Six dog/handler teams participated in 10 experiments, five of each kind. The reliability of an identification, or the diagnostic ratio, is the percentage correct identification in suspect = perpetrator experiments divided by the percentage false identification of the suspect in suspect not equal to perpetrator experiments. Factors that influence the reliability of scent identifications are discussed, and the results of the scent identifications are compared with recent reliability estimates of other forensic techniques.
Article
Determining the cellular content of saliva by means of conventional microscopy chamber counting is a very time-consuming and operator-sensitive procedure. This study concentrated on the use of flow cytometry to examine the cellular content of saliva. Erythrocytes, leukocytes, epithelial cells and bacteria were quantified and the results were compared with caries experience and the presence of gingivitis. 258 uncentrifuged vortexed paraffin-stimulated saliva samples (112 males and 146 females) were analyzed with the UF-100 flow cytometer. Salivary reference values were established for erythrocyte, leukocyte, epithelial cell and bacterial count. Caries experience (DMF) and the presence of gingivitis were recorded. Caries experience or caries risk could not be assessed with flow cytometry. However, salivary flow cytometry may be useful in determining an individual's risk for gingivitis: a significant increase in salivary leukocytes was observed in individuals with gingivitis. At a cut-off level of 10(3) leukocytes micro l(-1) saliva, a sensitivity of 76% and a specificity of 45% was obtained. Other analytes were not significantly different between individuals with and without gingivitis. Flow cytometry of paraffin-stimulated human saliva seems a promising diagnostic or predictive tool and further investigations of diseases of the oro-pharyngeal loge, such as tonsillitis and periodontitis, should be carried out in the future.
Article
Anecdotal evidence and legend have suggested that bloodhounds are capable of trailing and alerting to a human by his or her individual scent. This same evidence may be presented to a court of law in order to accuse a particular suspect or suspects of a crime. There is little to no scientific evidence confirming the bloodhound's ability to trail and discriminate the scent of different individual humans. Eight bloodhounds (3 novice and 5 veteran), trained in human scent discrimination were used to determine the reliability of evidence, garnered through the use of bloodhounds, in a court of law. These dogs were placed on trails in an environment that simulated real-life scenarios. Results indicate that a veteran bloodhound can trail and correctly identify a person under various conditions. These data suggest that the potential error rate of a veteran bloodhound-handler team is low and can be a useful tool for law enforcement personnel.
Article
In a scent identification line-up, a trained dog matches the scent trace left by a perpetrator at the crime scene to the odour of a suspect in a line-up of different odours. The procedures are strictly defined and the results are routinely used by the police and as evidence in court in a number of European countries. This paper describes the effect of ageing of the odour trace collected at the crime scene on the performance of the dogs in recognising the perpetrator in a line-up. The results show that whilst the dogs perform faultlessly in matching odours collected on the same day, the results drop to a lower level and become more variable in the period studied (2 weeks to 6 months). However, the results do not show a systematic decrease in performance. A possible explanation is the development of a steady state in the glass jars containing the perpetrator odour trace after initial differential evaporation of components of the residue or break down of unsaturated components into saturated ones. Prevention of this initial change may prevent the drop in performance observed in this study, thus increasing the reliability of these scent identifications.
Article
Dogs have the ability to determine the direction of an odour trail left by a human. This study examined how much olfactory information from this trail is required by dogs to determine direction. Six dogs, able to determine direction, were tested on a 21 footstep trail laid on 21 individual carpet squares, one footstep per square, by the same individual wearing the same shoes. Dogs brought in at right-angles to the trail at its centre were able to correctly determine direction better than chance (P < 0.025). Dogs were unable to determine direction when the order of the footsteps was randomized by rearranging the order of the carpet squares. When the individual odour cue was removed, but ground disturbance left, dogs were unable to determine direction, indicating that it was the odour of the individual that was used to determine direction. In the final experiment the number of footsteps made available to the dog was reduced from 21 to 11 and then 9, 7, 5 and finally 3. Dogs were able to determine direction from 5 footsteps but not 3. It was calculated that it takes approximately 1-2 s for the odour information in footsteps to change to provide discernible information that can be used by dogs to determine direction. The process by which dogs may determine direction from odour cues is discussed.
Article
Although saliva or oral fluid "lacks the drama of blood, the sincerity of sweat and the emotional appeal of tears", quoting Mandel in 1990 [I.D. Mandel, The diagnostic uses of saliva, J. Oral Pathol. Med. 19 (1990) 119-125], it is now meeting the demand for inexpensive, non-invasive and easy-to-use diagnostic aids for oral and systemic diseases, drug monitoring and detection of illicit use of drugs of abuse, including alcohol. As the salivary secretion is a reflex response controlled by both parasympathetic and sympathetic secretomotor nerves, it can be influenced by several stimuli. Moreover, patients taking medication which influences either the central nervous system or the peripheral nervous system, or medication which mimic the latter as a side effect, will have an altered salivary composition and salivary volume. Patients suffering from certain systemic diseases may present the same salivary alterations. The circadian rhythm determines both the volume of saliva that will and can be secreted and the salivary electrolyte concentrations. Dietary influences and the patient's age also have an impact on composition and volume of saliva. The latter implies a wide variation in composition both inter- and intra-individually. Sampling must therefore be performed under standardized conditions. The greatest advantage, when compared to blood sample collection, is that saliva is readily accessible and collectible. Consequently, it can be used in clinically difficult situations, such as in children, handicapped and anxious patients, where blood sampling could be a difficult act to perform.
Article
A simple noninvasive procedure for saliva sample collection and DNA extraction was developed. On average, the amount of human DNA (as measured by a TaqMan-based assay) was about 11.4 microg/mL saliva, which is more than can be obtained from other noninvasive samples such as cheek swabs. However, the presence of large amounts of nonhuman DNA (up to 90% of the total extracted DNA) in saliva samples does necessitate DNA quantitation methods that are specific for human DNA. We were able to reliably and accurately type different genetic markers (mDNA sequences, Y-chromosomal single-nucleotide polymorphisms, and autosomal microsatellite loci) from saliva samples stored for up to 30 days at 37 degrees C, making this method well-suited for field conditions and convenient transportation of samples back to the laboratory. Thus, saliva can be considered a reliable source of DNA for a wide variety of genetic studies.
Article
The Scent Transfer Unit (STU-100) is a portable vacuum that uses airflow through a sterile gauze pad to capture a volatiles profile over evidentiary items for subsequent canine presentation to assist law enforcement personnel. This device was evaluated to determine its ability to trap and release organic compounds at ambient temperature under controlled laboratory conditions. Gas chromatography-mass spectrometry (GC-MS) analyses using a five-component volatiles mixture in methanol injected directly into a capture pad indicated that compound release could be detected initially and 3 days after the time of collection. Additionally, 15 compounds of a 39-component toxic organic gaseous mixture (10-1000 parts per billion by volume [p.p.b.(v)]) were trapped, released, and detected in the headspace of a volatiles capture pad after being exposed to this mixture using the STU-100 with analysis via GC-MS. Component release efficiencies at ambient temperature varied with the analyte; however, typical values of c. 10% were obtained. Desorption at elevated temperatures of reported human odor/scent chemicals and colognes trapped by the STU-100 pads was measured and indicated that the STU-100 has a significant trapping efficiency at ambient temperature. Multivariate statistical analysis of subsequent mass spectral patterns was also performed.
Article
Self-collection of saliva has the potential to provide molecular epidemiologic studies with DNA in a user-friendly way. We evaluated the new Oragene saliva collection method and requested saliva samples by mail from 611 men (ages 53-87 years). We obtained a response rate of, on average, 80% [varying from 89% (ages 67-71 years) to 71% (ages 77-87 years)]. DNA was extracted from 90 randomly selected samples, and its usefulness was evaluated with respect to quality, quantity, and whole-genome amplification (WGA). Visual inspection of DNA on agarose gels showed high molecular weight DNA (>23 kb) and no degradation. Total DNA yield measured with PicoGreen ranged from 1.2 to 169.7 mug, with a mean of 40.3 mug (SD, 36.5 mug) and a median of 29.4 mug. Human DNA yield was estimated by real-time PCR of the human prothrombin gene to account for 68% (SD, 20%) of total DNA. We did WGA on 81 saliva DNA samples by using the GenomiPhi DNA kit and genotyped both saliva DNA and WGA DNA for 10 single-nucleotide polymorphisms randomly selected from the human genome. Overall genotyping success rate was 96% for saliva DNA and 95% for WGA DNA; 79% of saliva DNA samples and 79% of WGA DNA samples were successfully genotyped for all 10 single-nucleotide polymorphisms. For the 10 specific assays, the success rates ranged between 88% and 100%. Almost complete genotypic concordance (99.7%) was observed between saliva DNA and WGA DNA. In conclusion, Oragene saliva DNA in this study collected from men is of high quality and can be used as an alternative to blood DNA in molecular epidemiologic studies.
Article
The composition of human scent collected from the hands is of interest to the medical community as a mechanism to diagnose disease and the forensic community as a means to investigate canine scent discriminations. An extensive survey of the volatile organic compounds (VOCs) identified in the headspace of hand odor samples utilizing solid phase micro-extraction gas chromatography/mass spectrometry (SPME-GC/MS) has been conducted to determine the constituents of the human base odor profile. Sixty-three compounds were extracted from the collected odor samples. The composition included acids, alcohols, aldehydes, hydrocarbons, esters, ketones and nitrogen-containing compounds. The majority of the compounds detected (79.4%) were present in less than one third of the individuals sampled. Spearman correlation coefficient comparisons at a match/no-match threshold of 0.9 produced a distinguish ability of 99.67% across the population.
Article
Bloodhounds are used to trail fleeing felons and missing persons. In order to start a trail, the dog must be presented with a person's scent. There are many hypotheses on what a bloodhound smells while trailing. The present study attempts to identify whether human scent is genetic, and if it is influenced by one's environment. Bloodhounds trained in human scent discrimination were used to differentiate between monozygotic twins, related and nonrelated persons, living together and apart. The first test required the dogs to run blind trails after being presented with the scent of one person in the pair, while the opposite person was hidden. The second test allowed the dogs to trail one person in the pair after both people were hidden. Results appear to demonstrate that bloodhounds rely heavily on genetic cues when differentiating between people. Environmental cues do not appear to significantly aid the bloodhound in scent discrimination.
Article
Whole saliva is a complex mixture of proteins and other molecules which originate from several sources. The biochemical and physicochemical properties of saliva contribute to the numerous functions of saliva in, e.g., speech, maintaining oral and general health, and food processing. Interest in saliva has increased in the last few years for its potential to diagnose viral, bacterial and systemic diseases. The use of saliva as research material may pose particular problems due to its inherent variability and instability. This review describes practical aspects of salivary as research material with emphasis on protein biochemistry and physical chemistry.