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MATCH: A New Approach for Differentiating & Linking Series of Sex Worker Homicides and Sexual Assaults
Abstract
Sex workers as a group are one of the more common targets in serial homicide, yet the most likely to go unsolved. Part of the reason for this is the difficulty in linking individual crime scenes to a series, especially in those series where offenders not only target sex worker victims but also target non-sex worker victims. Inconsistencies in both victim targeting and behaviors engaged in across series add to the difficulties of linking and solvability in these types of crimes. The current study aimed to add to the current body of literature on serial crime linkage by examining not only the most salient behavioral indicators useful for crime scene classification of serial homicides that involve sex worker victims but also examine the trajectories of behavioral change that can help link apparently inconsistent crime scenes and proposes the new Model for the Analysis of Trajectories and Consistency in Homicide (MATCH). The study examines 83 homicide series, including 44 (53%) series where all victims were sex workers and 39 (47%) series that included a mix of sex workers and non-sex worker victims. Using the MATCH system allowed for the majority of series to be classified to a dominant trajectory pattern, over half as many as a traditional consistency analysis that focusses on behavioral similarity matching. Results further showed that Sex Worker Victim series were almost three times more consistent across their series than Mixed-Victim series, not only in victim selection but also in the overall behavioral patterns. Findings are discussed in line with theoretical and psychological issues relating to understanding the nature of behavioral consistency and the importance of going beyond simple matching toward a model that allows for the identification of consistency in seemingly inconsistent series, as well as investigative implications relating to linking serial crimes.
... In addition to these papers, there are also research studies from Japan (Yokota et al., 2015(Yokota et al., , 2017a and Australia (Davidson & Petherick, 2020), and two further studies with a multi-national sample of crimes (Tonkin et al., 2017;Woodhams et al., 2019). Yokota et al., (2017aYokota et al., ( , 2017b and Woodhams et al. (2019) also 1 Pair-wise analysis has incorrectly been criticised to be investigating whether offenders show absolute consistency in their crimes (i.e., an identical pattern of individual behaviors across different crimes) and that failing to find this "causes great difficulties in linking" in practice (e.g., Sorochinski & Salfati, 2018;Salfati & Sorochinski, 2019). To be clear, when testing the underpinning principles of crime linkage using the pairwise analysis approach, "an identical pattern of individual behaviors between crimes" is not required. ...
... In addition, in Salfati (2008), Salfati noted a limitation common to many studies in investigative psychology (including crime linkage studies) which is that samples are often limited to legal categories of crime (e.g., rapes, sexual murders), whereas some offenders' series contain crimes that span legal categories. A recent study by Salfati and Sorochinski (2019) has investigated behavioral consistency in series of homicides where not all offenses in a series were actually homicides, but instead for some the victim was left alive. Recent research by Lovell et al. (2020) has noted the versatility seen in the offending of rapists whereby they commit a range of non-sexual crimes as well as sexual crimes. ...
Crime linkage can be a useful tool in the investigation of sexual offenses when other, physical evidence is unavailable or too costly to process. It involves identifying behavior that is both consistent and distinctive, and thus forms an identifiable pattern through which a series of offenses committed by the same offender can be distinguished. While there is a substantial body of research to support the principles of crime linkage, samples often contain only one type of sexual offense, and further research is needed into offenses such as voyeurism and exhibitionism. In practice, there are a number of ways in which crime linkage can be conducted, and a variety of terms are used to describe these different processes. While writings from practitioners provide insight into how crime linkage is conducted, research now needs to focus more on systematically mapping its practice and documenting procedural differences. There are also a number of additional considerations that require further research attention where the practice of crime linkage is concerned, such as the utility of computerised databases designed to assist with the process, the human decision-making element of linking and how bias can affect this, and the effects of expertise and training on linkage efficacy.
... Also, they noted that the lethal outcome of their sexual victimization was associated with substance abuse, use of coercion and humiliation, as well as a lack of premeditation (i.e., victim was randomly selected and no weapon was brought to the crime scene) and a lack of forensic awareness strategies to avoid detection (e.g., victim's body was left at the crime scene; Horan & Beauregard, 2018). Different motivational patterns were also found among series of sex-trade workers homicides and sexual victimization studied by Salfati and Sorochinski (2019), Chan (2019), and (2021)) also examined the characteristics of lethal sexual victimization of female sex-trade workers and found distinctive characteristics. Notably, the authors found that this form of victimization was typically committed by white male aged in their early 30s, and in highly populated areas (Chan & Beauregard, 2019). ...
Although relatively rare, sexual homicide has stimulated research efforts to better understand and intervene in the prevention of such crime. However, specific high-risk victims such as sex-trade workers have been understudied. To contribute to the limited scientific literature on this topic, the current study examines the characteristics of the sexual victimization of sex-trade workers using a sample of 402 lethal and non-lethal cases. Bivariate and multivariate analyses indicated that the lethal outcome associated with the sexual victimization of sex-trade workers may not be associated with sadism and paraphilic behaviors, but rather by excessive violence and victim's vulnerabilities. Conjunctive analysis further indicated that the combination of excessive violence, victim's intoxication, situational factors, and crime characteristics was associated with the lethal sexual victimization of sex-trade workers. Findings suggest strategies for the development of situational prevention and intervention strategies.
... To understand how these series may be effectively linked, it is, therefore, necessary to look more closely at the progression of both victimization patterns (e.g., at what point in the series do the offenders switch victims, do they go back and forth in the victim selection, or do they start off with one type and then move on to consistently victimizing another type of victim) and behavioral patterns (e.g., do offenders escalate or de-escalate in their crime type, going from assaulting the victim to killing the next or vice versa). Understanding these patterns will further our understanding of these complex crimes and likely bring us closer to devising behavioral models that would be effective for investigative linkage of these series (see Salfati & Sorochinski, 2019, for further discussion). ...
Contrary to popular misconceptions, offenders who kill sex workers as part of their series exhibit substantial variability in their victim selection and behavioral patterns, thus creating additional issues for the investigation of these crimes. This article first aims to outline differences in the demographics of crime scene actions present in homicide series with exclusively sex worker victims and series that includes both sex worker and non–sex worker victims, with the aim of understanding the crime scene aetiology of these two different types of series. Second, the research aims to determine between-series differences of victimology as well as crime scene action between sex worker series and mixed-victim series. Third, the research focuses on mixed-victim series and aims to determine the within-series similarities of victimology and crime scene actions, that is, what factors link sex worker victims and non–sex worker victims in the same series. Data were collected through a large-scale review of international media sources to identify solved serial homicide cases that have included at least one sex worker. Of the 83 series looked at, 44 (53%) included sex worker victims only, and 39 (47%) of the series included both sex worker and non–sex worker victims. The findings highlight the challenges that these types of crime present for investigation and the implications they have on current crime analysis research and practice, and results are discussed in line with theoretical and psychological issues relating to understanding differentiation and similarity, as well as investigative implications relating to linkage blindness and linking of serial crimes.
Prior research has associated Craigslist.com and Backpage.com as sources of victimization, which in part resulted in the closure of the erotic services of each respective website. However, research also claims the introduction of Craigslist was associated with a reduction in female homicide rates across 30 large cities. This research acts as a supplemental analysis to Cunningham et al. by analyzing if Backpage.com, considered to be Craigslist’s successor, has similar effects on female homicide rates. When including measures of interest in each respective website, we find that Backpage is associated with a decrease in homicide rates for women. The purpose of this study is to extend the study conducted by Cunningham et al. through supplemental analysis. To determine the effect of online clearinghouses on female homicide rates, interest measures in Backpage along with the female homicide rates from 120 single city metropolitan and micropolitan areas over 14 years (2004–2018) were analyzed using multiple regression analyses. The regression analyses show that there is a statistically significant relationship between interest in Backpage and homicide rates for women. We find that Backpage is associated with a decrease in homicide rates for women.
Behavioural crime linking refers to the practice of trying to tie two or more offences to the same offender using behaviour observable at the crime scene. It rests on the assumptions that offenders behave consistently enough from one offence to another, and distinctively enough from other offenders allowing offences to be successfully linked together. Conceptualised in the 70s, and developed methodologically with increased scientific rigour from the 90s, the last decade has seen a sharp rise in published studies on behavioural crime linking. From empirical validation of the underlying assumptions to mapping out practice and more ecologically valid tests of linkage accuracy, the field has developed considerably. Considering that investigating homicide is resource intensive, not to mention serial homicide, reliable and valid behavioural crime linking has the potential to aid and prioritise investigative avenues and help solve serial homicide.
Most studies on serial homicide have been carried out on North American samples. While some research has studied the consistency and distinctiveness of serial homicide offenders, few have empirically tested models of behavioural crime linking and linkage accuracy with serial homicide. Another shortcoming in behavioural crime linking research is the use of mostly serial cases to model crime linking, even though real crime databases include both serial and one-off offences. Some studies have tested the effect of added one-offs on the linkage accuracy of burglary and rape, but none so far the effect this would have on homicide. Additionally, while some studies have compared serial homicide offences to one-off homicides, none have tested whether it would be possible to predict whether a homicide belongs to a series or is a singular offence. Cognitive bias, especially confirmation bias or the expectancy effect, has been shown to have a considerable effect on crime investigation. No studies to date have explored the effect of such bias in behavioural crime linking.
The general aim of the thesis was to increase ecological validity of behavioural crime linking research, especially with regard to sampling choices and analyses that strive to answer questions relevant for homicide investigation. The main sample consisted of 116 Italian serial homicides, committed in 23 separate series of homicide. Additionally, information about 45 cases of hard-to-solve one-off homicide was gathered, coded, and added to the sample. Study I found seven behavioural dimensions of offending (e.g., sexually motivated homicides and aspects of control-behaviour) in line with previous research. Notably, also other motives than sexual were found in the killings. A majority of offences (63%) were correctly classified to their actual series in the predictive part of the study. Study II was an experiment that investigated whether knowledge of series membership increased perceived (coded) behavioural similarity in homicides committed by the same offender. While no support was found for a strong expectancy effect, the experimental task may have lacked in sufficient complexity, and replication is thus needed. Study III found several key differences between serial and singular homicides and was able to successfully use these differences to predict with good accuracy whether an offence was part of a series. Study IV combined all the advances in the methodology thus far and showed that behavioural crime linking was still viable even with a large proportion (10:1) of one-off homicides added into the sample. As a function of added one-off homicides, the specificity of the model worsened (more false positives), as did the proportion of offences belonging to a series found near the top of a ranked listing from more behaviourally similar to less behaviourally similar. Overall model accuracy remained good, though, further validating the practice of behavioural crime linking with more ecologically valid data.
The studies of the present thesis contribute to the methodology of behavioural crime linking research. Replication on local crime databases is needed to maximise the practical usefulness of the models in different jurisdictions. Going forward, a close-knit collaboration between researchers and practitioners is called for, to keep the research relevant for practice and to develop evidence-based practice. As we gain a clearer picture of the accuracy and error rate of behavioural crime linking models, their usefulness increase in both the criminal investigative phase and in the trial phase with behavioural crime linking being presented as expert evidence.
In the decade since the publication of the first edition of The Cambridge Handbook of Forensic Psychology, the field has expanded into areas such as social work and education, while maintaining the interest of criminal justice researchers and policy makers. This new edition provides cutting-edge and comprehensive coverage of the key theoretical perspectives, assessment methods, and interventions in forensic psychology. The chapters address substantive topics such as acquisitive crime, domestic violence, mass murder, and sexual violence, while also exploring emerging areas of research such as the expansion of cybercrime, particularly child sexual exploitation, as well as aspects of terrorism and radicalisation. Reflecting the global reach of forensic psychology and its wide range of perspectives, the international team of contributors emphasise diversity and cross-reference between adults, adolescents, and children to deliver a contemporary picture of the discipline.
Investigative Psychology (IP) as an empirical field of study that focusses on the psychological input to the full range of issues that relate to the investigation of crime. IP focusses on three overall processes present in any investigation that can be improved by psychological study; 1) Retrieving information from the crime scene for the purpose of analysis and research; 2) Making decisions during criminal investigations; and 3) Analysing criminal behaviour. For this last component, three general interlinked areas have been the focus of research: individual differentiation which aims to establish differences between the behavioral actions of offenders and identify subgroups of crime scene types; behavioural consistency which aims to understand an offender’s behavioural consistency across a series of crimes; and inferences about offender characteristics, which aims to establish the nature of the consistency between the most likely characteristics of an offender based on the way an offender acts at the time of the crime, and is at the core of offender profiling.
Three general interlinked areas have been the focus of offender profiling research: individual differentiation (establishing differences between the behavioral actions of crime scene types), behavioral consistency (understanding behavioral patterns across a series of crimes), and offender profiling (linking sub-types of crime scene patterns to the most likely characteristics of an offender). Taken together, these three areas form the empirical basis necessary for use in criminal investigations. However, studies supporting inferences about offender characteristics have to date been the least developed in the field of offender profiling. For profiling to be fully useful to investigations, a clear understanding of three main elements is crucial to fully develop, notably (1) what individual crime scene characteristics are the most salient to use; (2) what elements of the full series behavioral developmental pattern are important to understand as an additional factor; and (3) what offender characteristics are the most empirically robust to focus on for investigative use. The current study examines 80 series of serial homicide, involving 302 crime scenes. Using the key elements of an offender’s crime scene behavioral patterns shown to help link and differentiate crime scenes and series, the current study linked these to sub-sets of different offender characteristics, identified as most useful for investigations. These included such characteristics such as age at the start of the series, criminal history specialization, general history of violence, mental health history, and relationship to the victims in the series. Results are discussed in the context of implications for research and practical applications in serial crime investigation and offender profiling.
Sex workers are commonly claimed to be at heightened risk of fatal victimization. Although prior research indicates that the dynamics of sex worker homicides resemble sexual homicides more than nonsexual homicides, little is known about how these types of homicides compare in terms of offending patterns. This study considers a sample of 2,851 single‐victim, single‐offender homicide cases extracted from a 37‐year (1976–2012) US Supplementary Homicide Reports database, and compares the offender, victim, and offender characteristics of 243 sex worker homicides (189 males and 54 females) with those of 2608 sexual homicides (2474 males and 134 females). The findings suggest that the offender, victim, and offense characteristics of general, male‐offender, and female‐offender sex worker homicides are essentially different from the characteristics of sexual homicides. Logistic regressions further indicate that most offender, victim, and offense characteristics on the occurrence of general and male‐offender sex worker homicides were significantly associated with the perpetration of general and male‐offender sex worker homicides, with reference to sexual homicides. These findings offer insights relevant to the prioritization of criminal investigative practices.
For details of this work please see: https://www.researchgate.net/publication/331501355_Sex_Worker_Homicide_Series_Profiling_The_Crime_Scene
This article presents an analysis of occupational homicides of sex workers in the United Kingdom, 1990-2016. Characteristics of 110 people murdered between 1990 and 2016 are explored including the location of their murder, ethnicity, migration status, and gender. Key changes over time are noted including an increase in the number of sex workers murdered indoors as well as an increase in murdered migrant sex workers. By developing the concept of “occupational homicide,” we argue that sex worker homicide should be viewed as an occupational issue and that the distinction between work-related homicide and nonwork-related homicide should be accounted for in future studies and is essential to inform prostitution policy.
Purpose: This study compared the utility of different statistical methods in differentiating sexual crimes committed by the same person from sexual crimes committed by different persons.
Methods: Logistic regression, iterative classification tree (ICT), and Bayesian analysis were applied to a dataset of 3,364 solved, unsolved, serial, and apparent one-off sexual assaults committed in five countries. Receiver Operating Characteristic analysis was used to compare the statistical approaches.
Results: All approaches achieved statistically significant levels of discrimination accuracy. Two out of three Bayesian methods achieved a statistically higher level of accuracy (Areas Under the Curve [AUC] = 0.89 [Bayesian coding method 1]; AUC = 0.91 [Bayesian coding method 3]) than ICT analysis (AUC = 0.88), logistic regression (AUC = 0.87), and Bayesian coding method 2 (AUC = 0.86).
Conclusions: The ability to capture/utilize between-offender differences in behavioral consistency appear to be of benefit when linking sexual offenses. Statistical approaches that utilize individual offender behaviors when generating crime linkage predictions may be preferable to approaches that rely on a single summary score of behavioral similarity. Crime linkage decision-support tools should incorporate a range of statistical methods and future research must compare these methods in terms of accuracy, usability, and suitability for practice.
An increasing amount of research has been conducted on crime linkage, a practice that has already been presented as expert evidence in some countries; however it is questionable whether standards of admissibility, applied in some jurisdictions, have been achieved (e.g., the Daubert criteria). Much research has assessed the two basic assumptions underpinning this practice: that offenders are consistent in the way they commit their crimes and that offenders commit their crimes in a relatively distinctive manner. While studies of these assumptions with stranger sex offenses exist, they are problematic for two reasons: (1) small samples (usually N=50 series, 194 offenses; and N= 50 one-off offenses) and by sampling the offenses of both serial and one-off sex offenders, thereby representing a more ecologically valid test of the assumptions. The two assumptions were tested simultaneously by assessing how accurately 365 linked crime pairs could be differentiated from 29,281 unlinked crime pairs through the use of Leave-One-Out Cross-Validation logistic regression followed by Receiver Operating Characteristic analysis. An excellent level of predictive accuracy was achieved providing support for the assumptions underpinning crime linkage.
This study aimed to investigate the case linkage principles, behavioural consistency and distinctiveness, with a sample of serial car thieves. Target selection, acquisition, and disposal behaviours, as well as geographical and temporal behaviours, were examined. The effects of temporal proximity and offender expertise were also investigated as moderating factors of behavioural consistency. As in previous case linkage research, geographical and some target selection behaviours were able to predict whether crime pairs are linked or unlinked at a statistically significant level. Crucially, it was also found that temporal behaviours demonstrate a significant capability to predict linkage status, a variable which has never before been applied to the prediction of linkage in serial car theft. Furthermore, it was demonstrated that changing the operationalisation of the behavioural domains can affect the results obtained. No support was found for the moderation of behavioural consistency on the basis of temporal proximity or expertise. Overall, the results support previous case linkage studies, furthering their practical applicability within the criminal justice system. Copyright © 2012 John Wiley & Sons, Ltd.
This article presents the results of an empirical test of Holmes and Holmes’s serial murder classification scheme. Crime scene evidence from 100 U.S. serial murders, each the third in a distinct series, was content analyzed. The co-occurrence of content categories derived from the crime scene material was submitted to smallest space analysis. The features characteristic of the category of “power or control” killings were found to be typical of the sample as a whole, occurring in more than 50% of cases, and thus did not form a distinct type. Limited support was found for aspects of the lust, thrill, and mission styles of killing, but this support drew attention to differences in the ways victims were dealt with, through mutilation, restraints, or ransacking their property rather than the motivations implicitly inferred in Holmes and Holmes’s typology. The current results are presented as an empirical basis for the classification of serial killings on which more detailed models can be built.
This work includes a count of solved serial murder cases in the United States from 1970 to 2009. The number of serial murder cases has declined; the likelihood that a victim is a female has increased somewhat and although the numbers of all types of serial murder victims has declined, when a case occurs, victims are increasingly likely to be prostitutes, particularly female prostitutes. U.S. serial murder cases with prostitute victims accounted for 32% of all U.S. serial murder cases involving female victims only, 1970-2009. However, the proportion of solved cases involving female prostitute victims only increased across the study period from 16% during 1970-1979 to a high of 69% during 2000-2009. Prostitute killers amass a greater average number of victims than do nonprostitute killers and when analyzed by decade, those who kill primarily prostitutes, kill for slightly longer periods of time. The implications of findings for prevention and investigation efforts are discussed.
The present study aimed to identify dimensions of variation in serial homicide and to use these dimensions to behaviourally link offences committed by the same offender with each other. The sample consisted of 116 Italian homicides committed by 23 individual offenders. Each offender had committed at least two homicides. As some offenders had worked together and some murders involved more than one victim, there were 155 unique pairings of offenders and victims. Dichotomous variables reflecting crime features and victim characteristics were coded for each case. Using Mokken scaling, a nonparametric alternative to factor analysis, seven dimensions of variation were identified. Five of the dimensions described variations in the motivation for the killings. Three of these were concerned with aspects of instrumental motivation whereas two of the motivational scales described variations in sexual motivation. The two remaining dimensions dealt with the level of planning evident in the crime scene behaviour of the offender. Two dimensions were identified: one consisting of behaviours suggesting a higher level of control and another describing impulsiveness. Using discriminant function analysis with the dimensions as independent variables and the series an offence belonged to as dependent variable, 62.9% of the cases could be correctly assigned to the right series (chance expectation was 6.2%). The implications of the results for serial homicide investigations are discussed.
The empirical support for linkage analysis is steadily increasing, but the question remains as to what method of linking is the most effective. We compared a more theory‐based, dimensional behavioural approach with a rather pragmatic, multivariate behavioural approach with regard to their accuracy in linking serial sexual assaults in a UK sample of serial sexual assaults (n = 90) and one‐off sexual assaults (n = 129). Their respective linkage accuracy was assessed by (1) using seven dimensions derived by non‐parametric Mokken scale analysis (MSA) as predictors in discriminant function analysis (DFA) and (2) 46 crime scene characteristics simultaneously in a naive Bayesian classifier (NBC). The dimensional scales predicted 28.9% of the series correctly, whereas the NBC correctly identified 34.5% of the series. However, a subsequent inclusion of non‐serial offences in the target group decreased the amount of correct links in the dimensional approach (MSA–DFA: 8.9%; NBC: 32.2%). Receiver operating characteristic analysis was used as a more objective comparison of the two methods under both conditions, confirming that each achieved good accuracies (AUCs = .74–.89), but the NBC performed significantly better than the dimensional approach. The consequences for the practical implementation in behavioural case linkage are discussed. Copyright © 2012 John Wiley & Sons, Ltd.
Despite weaknesses in the
organized/disorganized classification of serial killers, it is drawn on for "offender profiles," theories of offending, and in murder trials. This dichotomy was therefore tested by the multidimensional scaling of the co-occurrence of 39 aspects of serial killings derived 100 murders committed by 100 U.S. serial killers. Results revealed no distinct subsets of offense characteristics reflecting the dichotomy. They showed a subset of organized features typical of most serial killings. Disorganized features are much rarer and do not form a distinct type. These results have implications for testing typologies supporting expert opinion or to help understand variations in criminal acts, as well as the development of a science of investigative psychology that goes beyond offender profiling. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
To examine if serial homicide offenders are consistent across their crimes, a model was developed empirically that could be used to distinguish between crimes that were instrumental and those that were expressive. The first known three offences in each series of 69 US serial homicides committed by 23 offenders, were examined and the instrumental and expressive themes determined. Three models were then explored that test for consistency across these themes. The most liberal model was found to classify all of the offences effectively and to reveal complete consistency across the three crimes for all offenders. The implications of these results for offender profiling and further study of serial homicide are discussed. Copyright © 2005 John Wiley & Sons, Ltd.
Personality psychologists have suggested that the context of a behaviour should be considered in studying behavioural consistency. They have operationalised this as studying ‘if (situation)–then (behaviour)’ contingencies and have demonstrated an association between situational similarity and behavioural consistency. Previous research of behavioural consistency in the forensic setting has tended to focus exclusively on the ‘then (behaviour)’ part of the contingency—the offender's behaviour. This paper considers methodological approaches that might be used to investigate whether situational similarity is associated with behavioural consistency, and to develop if–then contingencies. Seventy-eight offences by stranger sex offenders were subjected to constant comparison framework analysis to develop an offender behaviour checklist and a victim behaviour checklist, and a combination of constant comparison framework analysis and hierarchical cluster analysis were used to develop victim behavioural themes. Consistency in offender behaviour and similarity in victim behavioural themes (representing situational similarity) were measured using Jaccard's coefficient for offence pairs within 13 solved series of stranger sexual assaults. Correlational analyses were used to assess the relationship between situational similarity and behavioural consistency. Contrary to expectations, no relationship was found. The utility of linguistic computational programs in creating if(victim behaviour)–then(offender behaviour) contingencies was tested with encouraging results. However, little evidence of consistency in if(victim behaviour)–then(offender behaviour) contingencies was found within the offence series. Explanations are proposed for these novel findings and avenues for future research are suggested. Copyright © 2008 John Wiley & Sons, Ltd.
The purpose of this study is to determine if readily available information about commercial and residential serial burglaries, in the form of the offender's modus operandi, provides a statistically significant basis for accurately linking crimes committed by the same offender. Logistic regression analysis is applied to examine the degree to which various linking features can be used to discriminate between linked and unlinked burglaries. Receiver operating characteristic (ROC) analysis is then performed to calibrate the validity of these features and to identify optimal decision thresholds for linking purposes. Contrary to crime scene behaviours traditionally examined to link serial burglaries, the distance between crime site locations demonstrated significantly greater effectiveness as a linking feature for both commercial and residential burglaries. Specifically, shorter distances between crimes signalled an increased likelihood that burglaries were linked. Thus, these results indicate that, if one examines suitable behavioural domains, high levels of stability and distinctiveness exist in the actions of serial burglars, and these actions can be used to accurately link crimes committed by the same offender. Copyright © 2005 John Wiley & Sons, Ltd.
Purpose. Through an examination of serial rape data, the current article presents arguments supporting the use of receiver operating characteristic (ROC) analysis over traditional methods in addressing challenges that arise when attempting to link serial crimes. Primarily, these arguments centre on the fact that traditional linking methods do not take into account how linking accuracy will vary as a function of the threshold used for determining when two crimes are similar enough to be considered linked.Methods. Considered for analysis were 27 crime scene behaviours exhibited in 126 rapes, which were committed by 42 perpetrators. Similarity scores were derived for every possible crime pair in the sample. These measures of similarity were then subjected to ROC analysis in order to (1) determine threshold-independent measures of linking accuracy and (2) set appropriate decision thresholds for linking purposes.Results. By providing a measure of linking accuracy that is not biased by threshold placement, the analysis confirmed that it is possible to link crimes at a level that significantly exceeds chance (AUC = .75). The use of ROC analysis also allowed for the identification of decision thresholds that resulted in the desired balance between various linking outcomes (e.g. hits and false alarms).Conclusions. ROC analysis is exclusive in its ability to circumvent the limitations of threshold-specific results yielded from traditional approaches to linkage analysis. Moreover, results of the current analysis provide a basis for challenging common assumptions underlying the linking task.
Case linkage involves identifying crime series on the basis of behavioral similarity and distinctiveness. Research regarding
the behavioral consistency of serial rapists has accumulated; however, it has its limitations. One of these limitations is
that convicted or solved crime series are exclusively sampled whereas, in practice, case linkage is applied to unsolved crimes.
Further, concerns have been raised that previous studies might have reported inflated estimates of case linkage effectiveness
due to sampling series that were first identified based on similar modus operandi (MO), thereby overestimating the degree
of consistency and distinctiveness that would exist in naturalistic settings. We present the first study to overcome these
limitations; we tested the assumptions of case linkage with a sample containing 1) offenses that remain unsolved, and 2) crime
series that were first identified as possible series through DNA matches, rather than similar MO. Twenty-two series consisting
of 119 rapes from South Africa were used to create a dataset of 7021 crime pairs. Comparisons of crime pairs that were linked
using MO vs. DNA revealed significant, but small differences in behavioral similarity with MO-linked crimes being characterized
by greater similarity. When combining these two types of crimes together, linked pairs (those committed by the same serial
offender) were significantly more similar in MO behavior than unlinked pairs (those committed by two different offenders)
and could be differentiated from them. These findings support the underlying assumptions of case linkage. Additional factors
thought to impact on linkage accuracy were also investigated.
KeywordsComparative case analysis–Linkage analysis–Behavioral linking–Sexual assault–Sexual offense
This paper uses statistical models to test directly the police practice of utilising modus operandi to link crimes to a common offender. Data from 86 solved commercial burglaries committed by 43 offenders are analysed using logistic regression analysis to identify behavioural features that reliably distinguish between linked and unlinked crime pairs. Receiver operating characteristic analysis is then used to assign each behavioural feature an overall level of predictive accuracy. The results indicate that certain features, in particular the distances between burglary locations, lead to high levels of predictive accuracy. This study therefore reveals some of the important consistencies in commercial burglary behaviour. These have theoretical value in helping to explain criminal activity. They also have practical value by providing the basis for a diagnostic tool that could be used in comparative case analysis.
This timely handbook provides in-depth overviews of the myriad and multi-faceted issues surrounding sexual assault and its pervasiveness in today’s culture. Drawing for multiple viewpoints and experts, the book is divided into seven comprehensive sections, covering such topics as risk factors, varying theoretical frameworks, prevention and intervention, and special populations. Within these sections the authors provide historical background as well as the latest research, and offer treatment outcomes and potentials.
Selected topics covered in this book include:
• Feminist theories of sexual assault
• Social and economic factors surrounding sexual violence
• Mental, physiological, physical, and functional health concerns of victims, including PTSD
• Major categories of sexual offenders
• Treatment of sexual assault survivors in the LGBTQ+ community
• Procedural processes related to sexual assault investigation and adjudication within the criminal justice system
The Handbook of Sexual Assault and Sexual Assault Prevention is a vital book that will appeal to a broad spectrum of students, researchers, practitioners, and clinicians in the fields of psychology, psychiatry, community mental health, and sociology.
Contrary to popular misconceptions, offenders who kill sex workers as part of their series exhibit substantial variability in their victim selection and behavioral patterns, thus creating additional issues for the investigation of these crimes. This article first aims to outline differences in the demographics of crime scene actions present in homicide series with exclusively sex worker victims and series that includes both sex worker and non–sex worker victims, with the aim of understanding the crime scene aetiology of these two different types of series. Second, the research aims to determine between-series differences of victimology as well as crime scene action between sex worker series and mixed-victim series. Third, the research focuses on mixed-victim series and aims to determine the within-series similarities of victimology and crime scene actions, that is, what factors link sex worker victims and non–sex worker victims in the same series. Data were collected through a large-scale review of international media sources to identify solved serial homicide cases that have included at least one sex worker. Of the 83 series looked at, 44 (53%) included sex worker victims only, and 39 (47%) of the series included both sex worker and non–sex worker victims. The findings highlight the challenges that these types of crime present for investigation and the implications they have on current crime analysis research and practice, and results are discussed in line with theoretical and psychological issues relating to understanding differentiation and similarity, as well as investigative implications relating to linkage blindness and linking of serial crimes.
Chapter summary
• Sex worker victims are the single most targeted group in serial homicide offenses
• Only a subgroup of offenders consistently victimize sex workers, while others target both sex workers and other types of victims
• For offenders who target multiple types of victims, sex workers are only a part of their generalized pattern of violence and sex offending across their series
• Offenders who target multiple types of victims can further be differentiated based on the pattern of victim selection and type of activity with each type of victim, including sexual activity and level of violence
• Expanding our understanding of series composition and trajectories can increase linkage efforts by moving from focusing on only a single victim type (e.g., sex workers) or only a single crime type (e.g., sexual assault vs. sexual homicide) and by so doing, increase solvability
Book synopsis: As a society we are buying more sex than ever before. Adult sex shops now take their place amongst retailers in the high street and lap dancing clubs compete for an increased share of the leisure economy; hotel chains offer sexually explicit films as part of their standard service, the party selling of adult toys to women in their homes has become a mainstream activity; and at the traditional end of the sexual service economy, prostitution has experienced new growth. Along with this has come new legal measures and attempts to regulate the sexual leisure economy, and far more comprehensive plans than ever before to regulate prostitution, in particular in the form of the new Sex Offences Act. This book seeks to address the range of issues and contemporary debates on the sex industry, including the demand by customers who buy sex, the policing of women who work in the street sex industry, and the violence that pervades prostitution. It shows how these issues have been addressed in policy terms, the problems that have emerged in this, and how a social policy might be formulated to minimize harm and enhance public understanding. Overall the book aims to provide a critical perspective on prostitution policies and the legal chaos and complexities that surround this.
Whilst investigative use of behavioural evidence to help link and solve serial offences has long been in use, the empirical and theoretical grounds for whether and how to use this evidence effectively have begun to emerge only in recent decades. The present study empirically tested (a) the potential for effectively differentiating between rape offence crime scenes using quantitative and qualitative distinctions within the behavioural dimensions of control, violence, and sexual activity, and (b) the extent to which redefining behavioural consistency more broadly to include dynamic trajectories of behavioural change may be more effective than limiting this definition to behavioural stability. Results confirmed that sexual offences can be successfully differentiated based on the specific degree and subtype of these behavioural dimensions present in each crime scene. The analysis of consistency and behavioural trajectories showed that whilst none of the offenders exhibited complete consistency across behavioural dimensions, a subsample of offenders remained fully consistent in at least one. Furthermore, of those who were not consistent, the vast majority followed an identifiable trajectory of change. Findings are discussed in the context of psychological theories of behavioural consistency as well as practical aspects of advancing the utility of behavioural linkage.
Policy development to tackle the issue and promote prevention of sexual abuse seems to be driven by the assumption that sexual offenders are characterized by some pathology, which prevents them from controlling their sexual urges and renders them more likely to reoffend if they live close to places where children congregate. The chapter examines whether or not crime commission patterns in sexual offenders change over time or from one victim to another. It also examines whether or not strategies adopted to commit offense and associated outcomes vary across time. It classifies offenders as escalators, specialists, or de-escalators based on strategies and sexual behaviors performed on victim. It then assesses the synchronicity of changes in offender strategies and sexual behaviors performed during the offense over time. It also looks at presence of covariates for both strategies and sexual behaviors in order to explain the nature of switching over time, if any.
Recent literature suggests that different ‘styles’ of homicide will most appropriately be reflected in the different types of behaviours committed by offenders during the crime. In the last few years, there has been a move to standardise classification systems of single homicides and establish their cross-national generalisability. Literature on serial homicide to date has mostly centred on homicides occurring in the US. However, national differences due to factors such as culture, national identity, political, and socio-economic circumstances may decrease the applicability of these models or certain aspects thereof in other countries and thus must be evaluated. The present study tested the applicability in the South African context of a recently developed US-based serial homicide crime scene classification framework. Specifically, this study compared the thematic differentiation in planning and violent behaviours that the offenders engage in and how this differentiation compares with that in the US. The sample consisted of 25 homicides that were in total responsible for the murder of 267 victims. Results indicated that overall, the framework is useful and applicable in the South African sample, but important environmental and contextual constraints must be taken into account. Copyright © 2014 John Wiley & Sons, Ltd.
Key to understanding the significance of behavioural evidence for linkage purposes is in establishing how consistently an offender displays the same or similar behaviours across their series. There have however to date been very few studies aiming at identifying salient components of offending behaviour that can be used reliably for linking individual crimes as part of a single series. In addition, studies that have been conducted have all dealt with serial homicide in the Western world and have been based on small samples of cases from each country. Some of the recent literature has started to disentangle some of these salient features, notably the victim, violence levels, control, and planning. The current study focused on evaluating the consistency of these features across series, using a sample of serial homicides from South Africa consisting of 30 offenders with a total of 283 victims and 235 crime scenes. Results indicate that the level of interaction with the victim may be influential to the stability or instability of offending patterns across the series. How offenders approach planning in their offence also showed a certain degree of consistency, with patterns of violence being the least consistent across the series of all components tested. Copyright © 2014 John Wiley & Sons, Ltd.
Purpose. The study extends research by Santtila et al. (2008) by investigating the effectiveness of linking cases of serial homicide using behavioural patterns of offenders, analysed through Bayesian reasoning. The study also investigates the informative value of individual behavioural variables in the linking process. Methods. Offender behaviour was coded from official documents relating to 116 solved homicide cases belonging to 19 separate series. The basis of the linkage analyses was 92 behaviours coded as present or absent in the case based on investigator observations on the crime scene. We developed a Bayesian method for linking crime cases and judged its accuracy using cross-validation. We explored the information added by individual behavioural variables, first, by testing if the variable represented purely noise with respect to classification, and second, by excluding variables from the original model, one by one, by choosing the behaviour that had the smallest effect on classification accuracy. Results. The model achieved a classification accuracy of 83.6% whereas chance expectancy was 5.3%. In simulated scenarios of only one and two known cases in a series, the accuracy was 59.0 and 69.2%, respectively. No behavioural variable represented pure noise but the same level of accuracy was achieved by analysing a set of 15, as analysing all 92 variables. Conclusion. The study illustrates the utility of analysing individual behavioural variables through Bayesian reasoning for crime linking. Feasible applied use of the approach is illustrated by the effectiveness of analysing a small set of carefully chosen variables.
A series of stranger sexual assaults poses considerable obstacles for law enforcement officials. One such preoccupation is concerned with whether or not the offender will escalate in the severity of his behaviours with subsequent victims. The current study uses transition matrices to address whether or not the offending patterns of 72 serial stranger sex offenders change from one victim to the next as it pertains to their sexual acts and level of physical force used during the crime. Findings indicate that stability, specifically the offender's intrusive sexual acts and use of physical force, and versatility are present in this sample's offending patterns. To explain changes in offending patterns between victims, multinomial regression analyses indicate that situational factors and modus operandi strategies are important considerations. Implications for investigations are discussed. Copyright © 2013 John Wiley & Sons, Ltd.
The present study examines consistency of crime behaviour among 347 sexual assaults committed by 69 serial sex offenders. This individual behaviour approach—the so-called signature approach—reveals which features of crime behaviour are consistent across a series and which features are not. The consistency scores were calculated using the Jaccard's coefficient. The results of this study indicate that there are some crime features of a serial sexual assault that can be useful for the purpose of linkage. Another important finding is that consistency scores for different variables within the same category can differ substantially. Moreover, serial sex offenders are more likely to be consistent in their environmental crime features when they are also consistent in their behavioural features, and vice versa. Serial sex offenders are also more likely to be consistent in the behavioural features of their assaults as the crime series gets longer. The implications of the results are discussed in relation to both research and practise
Homicide grows out of a transaction between individuals. This transaction is a product of the individuals and their relationship. More may therefore be understood about different "styles" of homicide by examining how an offender acts toward a victim during the crime. The analysis of the actual behaviors used by offenders at 247 single offender-single victim homicide crime scenes indicated a pattern of frequencies that follow a continuum from where the offender reacts in an impulsive way toward the emotions engendered through the conflicted interpersonal relationship with the victim, to where the offender interacts with the victim much more at a removed level, both physically and emotionally. Behaviors can thus be seen to follow a thematic pattern that can be related to underlying psychological principles, which closely relate to how an offender interacts with the victim at the crime scene.
Recent literature suggests that different “styles” of homicide will most appropriately be reflected in the different types of behaviors committed by offenders at a crime scene. These distinctions, it has been proposed, can best be understood using an instrumental and expressive thematic framework to analyze the way the offender acts at the crime scene. Multidimensional analysis was carried out on the crime-scene actions of 210 Greek single-offender, single-victim stranger homicides, with the aim of replicating earlier studies. A multivariate structure resulted, encompassing both hypothesized themes, allowing 63% of the cases to be assigned to dominant styles. Results are discussed in terms of implications for cross-national similarities and differences in the thematic structure of homicide and in terms of future avenues for research.
One of the main areas of concern regarding offender profiling has been the general lack of extensive empirical studies on the psychological processes underpinning this process. This study aimed to investigate the possibility of establishing a model of homicide behaviors that could be used as a basis for evaluating the scientific validity of offender profiling. A sample of 247 British single offender-single victim solved homicide cases was analyzed using a nonmetric multidimensional scaling procedure known as Smallest Space Analysis. The results indicated that homicide crime scenes could most readily be differentiated in terms of the expressive and instrumental role the victim had to the offender. The backgrounds of the offenders could similarly be differentiated by an expressive/instrumental thematic split. However, when these two elements were combined, there was a substantial mix between crime scene themes and themes of background characteristics. The results are discussed in terms of the validity of classifying homicide into a expressive/instrumental dichotomy and the implications this classification may have for offender profiling.
The purpose of this paper is to identify and clarify the issues facing our society resulting from the phenomenon of serial murder. It will be argued that the extent and prevalence of serial murders in our society today is an indirect effect of the almost total lack of sharing or coordination of investigative information relating to unsolved murders and to the lack of adequate networking among law enforcement agencies in this country. This lack of coordination and networking will be referred to as linkage blindness. This inability of law enforcement to link unsolved murders to a serial pattern greatly increases the probability that this serial sequence of murders will continue until the murderer makes a mistake.
Recent literature suggests that different styles of homicide will most appropriately be reflected in the different types of behaviors committed by offenders at a crime scene. These distinctions, it has been proposed (e.g., Salfati, 2000), can best be understood using an instrumental and expressive thematic framework for the way the offender acts at the crime scene. Multidimensional analysis was carried out on the crime-scene actions derived from 75 Canadian single-offender, single-victim homicides, with the aim to replicate these earlier studies. A multivariate structure resulted, encompassing both hypothesized styles. Results are discussed in terms of implications for cross-national similarities and differences in the thematic structure of homicide and explorations regarding future avenues for research regarding crime-scene classification.
Through the use of detailed examples, Shye introduces readers to the use of facet theory as a method for integrating content design with data analysis. He shows how facet theory provides a strategy for conceptualizing a study, for formulating the study's variables in terms of its purposes, for systematic sampling of the variables, and for formulating hypotheses. The book is organized into 2 parts: Part [I] introduces the reader to mapping with specific emphasis on mapping sentences, and Part [II] explores procedures for processing multivariate data. The book concludes with a discussion on the nature of scientific inquiry and the difference between a research question and observational questions.
[This book] will provide researchers with a useful technique for constructing questionnaires and for designing research instruments. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Aimed at critically examining how offenders and offences are conceptualised, Investigative Psychology has seen a substantial increase in studies of crime scene behaviours and offender characteristics using multidimensional scaling (MDS) analyses that build thematic models of crime scene behaviours based on the co-occurrence variables and then testing the frameworks by determining if cases are dominant in a single thematic region. Although methods have been developed, issues that arise from using different methods and the effect on the results obtained have never been thoroughly discussed. Framed in the context of the evolution of how people have been classified in offender profiling research and elsewhere, this paper examines the established procedures used in MDS studies to determine dominance. Two methods—proportional versus the quantity of variables present—are compared across four levels of stringency within a framework of homicide offenders' criminal convictions. Results support the most common criterion used in prior studies of homicide and demonstrate that the subject of the framework or type of variables may dictate which method is more appropriate. The results strengthen the argument that a standard protocol for determining dominance should be adopted to increase consistency across studies to add to the development of Investigative Psychology. Copyright © 2009 John Wiley & Sons, Ltd.
A sample of serial stranger rape cases ( n = 43) that had occurred in Finland during the years 1983–2001 were studied with the objectives being to: (a) describe the characteristics of the offenders; (b) explore the structure of serial rape; and (c) demonstrate behavioural linkage through an analysis of the offenders' crime scene behaviour using both multidimensional scaling (MDS) and discriminant function analysis (DFA). The material was content analysed with regard to the occurrence of a number of dichotomous variables. The inter-relationships of the variables was studied using MDS. The analysis revealed two previously identified major modes of interaction with the victim: involvement and hostility. Employing MDS and DFA, it was shown that the offences of different offenders were distinguishable in terms of variation between the offences of different offenders and consistency within the offences of a single offender. Using DFA, the classification accuracy clearly exceeds that expected by chance, and 25.6% of the cases were classified without any error. The results are discussed in relation to their practical utility and previous studies. Copyright © 2005 John Wiley & Sons, Ltd.
Linkage analysis is a crucial part of the investigative process when faced with a possible series of related offences. Establishing behavioural consistency (i.e., offender's behaviours consistently present across the series) is at the core of linkage. Recent empirical studies have found little evidence of consistency looking at either individual or groups of behaviours in serial homicide. It is argued that behavioural changes are rooted in the changing cognitive strategies that offenders use to reach their ultimate goal (i.e. the commission of multiple homicides). Factors that could account for these changes include learning, situational factors, loss of control, and changes in the offender's fantasy. Patterns of behavioural change have been identified in serial crimes, such as rape. However, no empirical studies have looked at patterns of behavioural change in serial homicide. The present study examined patterns of consistency and change using a combination of thematic and behavioural subgroup approaches that use Multidimensional Scaling. Thematic differentiation indicative of behavioural manifestations of cognitive strategies was found in all three examined subgroups: planning, wounding, and offender–victim interaction, and patterns of change within these subgroups provided support for the above theories. Looking at behavioural patterns rather than individual behaviours, may be a more fruitful way of examining consistency in serial homicide, and could have significant implications for linkage analysis. Copyright © 2010 John Wiley & Sons, Ltd.
Purpose. The psychological hypotheses that form the foundations for ‘Offender Profiling’ are identified and the research that has tested them is reviewed. Argument. ‘Offender profiling’ is taken to be the derivation of inferences about acriminal from aspects of the crime(s) he or she has committed. For this process to move beyond deduction based on personal opinion and anecdote to an empirically based science, a number of aspects of criminal activity need to be distinguished and examined. The notion of a hierarchy of criminal differentiation is introduced to highlight the need to search for consistencies and variations at many levels of that hierarchy. However, current research indicates that the key distinctions are those that differentiate, within classes of crime, between offences and between offenders. This also leads to the hypothesis ofa circular ordering of criminal actions, analogous to the colour circle, a ‘radex’. The radex model, tested using Multi-Dimensional Scaling (MDS) procedures, allows specific hypotheses to be developed about important constituents of criminal differentiation: Salience. MDS analyses reveal the importance of the frequency of criminal actions as the basis on which the significance of those actions can be established. Models of differentiation. The research reviewed mainly supports distinctions between criminals in terms of the forms of their transactions with their explicit or implicit victims. Consistency. Offenders have been shown to exhibit similar patterns of action on different occasions. The most reliable examples of this currently are in studies of the spatial behaviour of criminals. Inference. Under limited conditions it is possible to show associations between the characteristics of offenders and the thematic focus of their crimes. In general these results provide support for models of thematic consistency that link the dominant themes in an offender's crimes to characteristic aspects of his or her lifestyle and offending history. Implications. Much of what passes for ‘offender profiling’ in practice and as reported in the factual and fictional media has no basis in empirical research. However, there are some promising results emerging in some areas of study. These results are most likely to be of value to police investigations when incorporated into decision support systems and the training of police officers. The results doalso provide new insights into the psychology o crime.
Jaccard has been the choice similarity metric in ecology and forensic psychology for comparison of sites or offences, by species or behaviour. This paper applies a more powerful hierarchical measure - taxonomic similarity (s), recently developed in marine ecology - to the task of behaviourally linking serial crime. Forensic case linkage attempts to identify behaviourally similar offences committed by the same unknown perpetrator (called linked offences). s considers progressively higher-level taxa, such that two sites show some similarity even without shared species. We apply this index by analysing 55 specific offence behaviours classified hierarchically. The behaviours are taken from 16 sexual offences by seven juveniles where each offender committed two or more offences. We demonstrate that both Jaccard and s show linked offences to be significantly more similar than unlinked offences. With up to 20% of the specific behaviours removed in simulations, s is equally or more effective at distinguishing linked offences than where Jaccard uses a full data set. Moreover, s retains significant difference between linked and unlinked pairs, with up to 50% of the specific behaviours removed. As police decision-making often depends upon incomplete data, s has clear advantages and its application may extend to other crime types. Copyright © 2007 John Wiley & Sons, Ltd.
Case linkage, the identification of crimes suspected of being committed by the same perpetrator on the basis of behavioral similarity, and offender profiling, the inference of offender characteristics from offense behaviors, are used to advise police investigations and, in relation to case linkage, have been admitted in legal proceedings. Criteria for expert evidence, such as the Daubert criteria (Daubert v. Merrell Dow Pharmaceuticals, 1993), place stringent conditions on the admissibility of expert evidence. The future contribution of these practices to legal proceedings depends, in part, on whether they are underpinned by hypotheses that are testable and supported. The 3 hypotheses of offender behavioral consistency, of offender behavioral distinctiveness, and of a homology (direct relationship) between offender characteristics and behavior were empirically examined using a sample of serial commercial robberies. Support was found for the former 2 hypotheses but not for the last. The findings of the 2 studies have implications for the future development of these practices, for legal practitioners evaluating expert evidence, and for the implementation of public policy.
An understanding of the nature of personality depends on clear conceptions of consistency. Researchers have applied the term consistency in ambiguous and inconsistent ways over the last half century, which has led to a great deal of confusion and debate over the existence of personality. This article seeks to reframe and extend conceptions of consistency and thus proposes three important ways consistency concepts differ from each other. The first way consistency concepts differ from each other is in the competing determinant of behavior that the consistency is across: time, situation content, or behavior content. The second way consistency concepts differ from each other is in the definition of behavior enactment: single enactment, aggregate enactment, contingent enactment, or patterned enactment. When these two dimensions are crossed with a third dimension-definition of similarity (absolute, relative-position, or ipsative)-they create a supermatrix of 36 consistency concepts. Empirical support for each of these 36 consistency concepts, or its failure, has uniquely different implications for the fundamental nature of personality. This supermatrix can serve as a guide for future research aimed at discovering the nature of personality.
The literature on "offender profiling" suggests that different "styles" of homicide will reflect differences in the background characteristics of the offender. To test this suggestion, hypotheses were drawn from studies of aggression to propose that murder crime scenes would reveal stylistic distinctions in the role of the aggression in the offense. It was further hypothesized that these distinctions would be clearest for those crime scene indicators that reflect the instrument (cognitive) actions that shape the offense rather than the more expressive (impulsive and emotional) components. Hypotheses about associated offender characteristics were also deduced on the assumption that the murder scene theme revealed the killers' typical styles of interpersonal transaction. To test these hypotheses MDS analyses were carried out on the crime scene and offender characteristics derived from 82 single offender, single victim stranger homicides. A multivariate structure resulted, including all three hypothesized styles, allowing 65% of the cases to be assigned to unique styles and a further 36% to be assigned to appropriate hybrids. Offender characteristics related in the anticipated way to the different crime scene styles, providing a basis for law enforcement inferences about offenders in stranger murders.
Prostitute women have the highest homicide victimization rate of any set of women ever studied. We analyzed nine diverse homicide data sets to examine the extent, trends, and perpetrators of prostitution-related homicide in the United States. Most data sources substantially under-ascertained prostitute homicides. As estimated from a conservative capture-recapture analysis, 2.7% of female homicide victims in the United States between 1982 and 2000 were prostitutes. Frequencies of recorded prostitute and client homicides increased substantially in the late 1980s and early 1990s; nearly all of the few observed pimp homicides occurred before the late 1980s. These trends may be linked to the rise of crack cocaine use. Prostitutes were killed primarily by clients, clients were killed mainly by prostitutes, and pimps were killed predominantly by pimps. Another conservative estimate suggests that serial killers accounted for 35% of prostitute homicides. Proactive surveillance of, and evidence collection from, clients and prostitutes might enhance the investigation of prostitution-related homicide.