Linking Crimes Using Behavioural Clues: Current Levels of Linking Accuracy and Strategies for Moving Forward

The number of published studies examining crime linkage analysis has grown rapidly over the last decade, to the point where a special issue of this journal has recently been dedicated to the topic. Many of these studies have used a particular measure (the area under the receiver operating characteristic curve, or the AUC) to quantify the degree to which it is possible to link crimes. This article reviews studies that have utilised the AUC and examines how good we are currently at linking crimes (within the context of these research studies) and what factors impact linking accuracy. The results of the review suggest that, in the majority of cases, moderate levels of linking accuracy are achieved. Of the various factors that have been examined that might impact linking accuracy, the three factors that appear to have the most significant impact are crime type, behavioural domain, and jurisdiction. We discuss how generalisable these results are to naturalistic investigative settings. We also highlight some of the important limitations of the linking studies that we reviewed and offer up some strategies for moving this area of research forward. Copyright © 2013 John Wiley & Sons, Ltd.     

Crime scene actions and offender characteristics in a sample of Finnish stranger rapes

The crime scene actions employed by offenders in stranger rapes were analysed in relation to offender characteristics. Data were drawn from an official police database and consisted of stranger rapes occurring in Finland between 1992 and 2001 (n = 100). The structure of dichotomous variables derived through a content analysis of crime scene actions and offender characteristics were analysed with non‐metric multidimensional scaling (MDS). The first analysis revealed three separate action themes, with thematic emphases on Hostility, Involvement or Theft. The MDS‐solution for offender characteristics suggested four themes: Conventional; Psychiatric/Elderly; Criminal/Violent; and Criminal/Property. Each case was assigned to one of the themes or as a hybrid in order to analyse the associations between action themes and characteristics. The only significant association was found between the action theme, Theft and characteristics theme Criminal/Property. The results are discussed in relation to previous research. Copyright © 2004 John Wiley & Sons, Ltd.     

South African Serial Homicide: Consistency in Victim Types and Crime Scene Actions Across Series

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.     

Comparing the Predictive Accuracy of Case Linkage Methods in Serious Sexual Assaults

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.     

The consistency of inconsistency in serial homicide: patterns of behavioural change across series

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.     

Serial homicide: an investigation of behavioural consistency

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.     

College Men's Perceived Likelihood to Perpetrate Sexual Aggression

This study implemented a prospective design to explore the relationship between college men's perceived likelihood to perpetrate sexual aggression and their perpetration of sexual aggression over a three-month interim (N = 414). Compared to men's report of their likelihood to use physical force to obtain sex play or sexual intercourse, college men reported higher levels of perceived likelihood to use arguments or pressure to obtain sex play or sexual intercourse as well as drugs and alcohol to obtain sexual intercourse. Prospective analyses revealed that the majority of men who perpetrated sexual aggression over the follow-up period indicated that they were at some risk to do so at the pretest assessment. Implications for sexual assault prevention programming are discussed.     

Construct validity and test-retest reliability of a date rape decision-latency measure

In two studies, the construct (convergent and discriminant) validity and test-retest reliability of a date rape decision-latency measure was examined. In Study 1, 174 college men completed measures related to sexual aggression and listened to an audiotaped simulation of a date rape, during which cues of nonconsent and force gradually escalated over time. Participants were instructed to respond, by pressing a button which recorded the latency of their decisions in seconds, if and when they believed the man depicted in the scenario should stop his sexual advances. Results demonstrated positive associations between prolonged decision latencies and sexually aggressive behavior, calloused sexual beliefs, acceptance of interpersonal violence, and sexual promiscuity. In Study 2, initial results were cross-validated in a sample of 102 college men, and discriminant validity was established as decision latencies were unassociated with measures of social desirability, alcohol consumption and drug use. Test-retest reliability assessed over a 2-week interval was .87.The authors wish to thank Alan Gross and Brian Marx for providing the audiotaped stimulus materials, Richard Marsh for writing the decision-latency computer program, Jason Hicks for assisting with programming, and the undergraduate research assistants for serving as experimenters.     

The acceptance of modern myths about sexual aggression scale: development and validation in German and English

Scales of rape myth acceptance (RMA) often yield low means and skewed distributions. This is proposed to be because of a change in rape-related beliefs toward more subtle content. Incorporating insights from racism and sexism research, a 30-item self-report scale measuring the acceptance of modern myths about sexual aggression (AMMSA) is presented. Across four studies (total N=1,279), the reliability and validity of parallel German and English versions of the AMMSA scale were examined. The results show that both language versions are highly reliable; compared with a traditional RMA scale, means of AMMSA scores are higher and their distributions more closely approximate normality. Cross-sectional and longitudinal analyses provide evidence for the AMMSA scale's concurrent and predictive construct validity.     

Spatial and environmental consistency in serial sexual assault

This study examines the crime patterns of 76 New Zealand serial sexual offenders in order to determine the extent to which offenders display locational consistency in their choice of crime locations. More specifically, the hypothesis was that there would be intraseries consistency in the distances travelled (spatial consistency) and the characteristics of the crime sites selected (environmental consistency) by serial sexual offenders. For spatial consistency to be tested, the distances travelled from home to offend and the criminal range for each offence series were analysed. Support was found for spatial consistency, and, in line with much overseas research, it was also found that the offenders typically did not travel very far from home to offend (median distance of 3 km). The environmental consistency measure was made up of various physical, temporal, and contextual variables that described the environmental characteristics of an offence. As hypothesised, it was found that offenders displayed intraseries environmental consistency in offence site selection beyond the level of that expected by chance. The implications of this both for understanding offender spatial decision making and for geographical profiling are discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

UK and Spanish stranger sexual offenders crime scene behaviours and previous convictions: A cross-cultural comparison

International comparisons of previous convictions (PC) and crime scene behaviours (CSB) of stranger sexual offences can inform offender profiling strategies; especially the degree to which pragmatic models cross validate across countries. The present study compared PC and CSB of 474 UK and 418 Spanish cases. CSB and PC were analysed using Chi-square. UK stranger sexual offenders displayed a higher proportion of all CSB analysed. UK offenders also had a significantly higher proportion of PC with the exception of violence offences. There were no significant differences in sexual pre-convictions. In both the UK and Spain the CSB ‘reference to the police’ was significantly association with the PC ‘Criminal damage’ no other similar significant associations were found. Explanations for these findings include differences between the countries in regards to: legislation, crime recording processes, data coding processes, with additional consideration of any cultural, environmental and contextual factors.     

South African Serial Homicide: A Victim‐Focused Behavioural Typology

This current study assessed the value of the Interpersonal Model in differentiating serial homicide offences in South Africa, notably in terms of how the offender may display behavioural patterns that are indicative of them dealing with the victim as a Person, an Object, or a Vehicle. The sample consisted of 302 offences committed by 33 offenders that occurred from 1953 to 2007 in South Africa. Multidimensional scaling analysis was used to test the Interpersonal Model and results indicated that crime themes did not directly correspond to the threefold model. Instead, two crime scene types were present: Victim as Object (where the focus was on tangible gains, interaction with the victim throughout the phases of the crime was limited, and victims included men and live women) and Victim as Vehicle (where the victim might be construed as a conduit through whom the offender could realise their specific psychological needs, the interaction was extensive, and victims tended to be vulnerable). South African serial homicides did not appear to have a specific sub‐theme of Victim as Person, suggesting that the themes engaged in centred more on instrumentally focused actions but in qualitatively different ways. However, victim types were integral to the overall behavioural model. Using the Victim as Object/Vehicle dichotomy, 85.7% of the offences could be seen to engage dominantly in one of the two patterns at the crime scene. This not only supported the results of a twofold model, but having these many offenders showing a dominant crime scene type also shows that the model is an excellent representation of serial homicide offending in South Africa. Copyright © 2014 John Wiley & Sons, Ltd.     

The interplay of modern myths about sexual aggression and moral foundations in the blaming of rape victims

Moral Foundations Theory proposes five intuition-based moral concerns: Care and Fairness (“individualizing foundations”) as well as Loyalty, Authority, and Sanctity (“binding foundations”). In studies carried out in Italy, Spain, and Germany, the authors examined how these concerns are associated with the acceptance of modern myths about sexual aggression (AMMSA), and how both jointly predict rape victim blaming. Overall, victim blaming was positively predicted by Authority and Sanctity, and negatively predicted by Care and Fairness. Although victim blaming was best predicted by AMMSA, moral concerns also contributed to its prediction, partly independently, partly mediated through AMMSA, and in the case of Sanctity in interaction with AMMSA. Discussion highlights how integrating moral foundations in the investigation of victim blaming and AMMSA across different cultural contexts may deepen our understanding of why, in each cultural context, victim blaming and related beliefs are resistant to change.     

The practice of crime linkage: A review of the literature

Crime linkage has been the subject of increasing attention in academic research. Research has found support for the principles of behavioural consistency and distinctiveness, which underpin crime linkage, but this does not provide direct evidence as to whether crime linkage is useful in practice. This literature review draws together documentation that refers to the practice of crime linkage, from assessing analysts' efficacy, to discussing the usage of computerised tools to assist with the linkage process, to providing a comprehensive outline of the process itself. The implications of the amount and type of information currently available are discussed, including the variations in practice and terminology that were explored. Avenues for future investigation and the manner in which future research could be conducted are set out in a research agenda.     

Age as a modifier of sexually aggressive attitudes in men

Male attitudes and behaviours related to imagined sexual aggression were investigated in 99 Finnish men (mean age 24.3 years). Structural equation modelling suggested that imagined sexual aggression was directly predicted by hostile masculine ideologies and past antisocial acts, and indirectly by subject age (hostile masculinity decreased with age). For more detailed analyses of age effects on attitudes, the subjects were split into an older and a younger group. A small group of incarcerated rapists (n = 8; mean age 33.4 years) was included for comparative purposes; these were similar in age to the older group (n = 34; mean age 31.5 years) and were given the same attitude items. The younger men and the rapists expressed significantly more hostility toward women and acceptance of rape myths, and had a higher likelihood of committing rape than older men. Although younger men accepted interpersonal violence and sexual dominance, their attitudes were not necessarily reflected in past sexually aggressive behaviours, as they were in the rapists who differed from the younger men mainly in terms of their past antisocial activities.     

Unravelling Crime Series Patterns amongst Serial Sex Offenders: Duration,Frequency, and Environmental Consistency

Crime linkage and the investigation of behavioural consistency amongst serial offenders has been a flourishing field of research over the past decade or so, especially with respect to serial sex offenders. The emerging research in this field has often portrayed serial sex offenders as a single, distinct, and homogeneous group. Such an assumption, however, has never been empirically examined. Using a criminal career approach and a sample of 72 serial sex offenders who have committed a total of 361 sexual assaults on stranger victims, the current study aims to examine and describe subgroups of crime series patterns amongst serial sex offenders in terms of duration and frequency of offending. The level of environmental consistency display (i.e. offender's choice of crime location and characteristics of the crime site selected) across subgroups of crime series patterns is also examined. Study findings suggest the presence and heterogeneity of crime series patterns amongst serial sex offenders, advocating for the consideration of subgroups of crime series patterns when studying serial sex offenders. Moreover, the offenders' level of environmental consistency varies across the different crime series patterns identified, allowing for the identification of subgroups of offenders showing a higher or lower level of environmental consistency. Copyright © 2014 John Wiley & Sons, Ltd.     

Statistical modelling in the investigation of stranger rape

A sample of stranger rape offences (n = 271) registered in the Dutch Violence Crime Linkage Analysis System database in the Netherlands between 1997 and 2007 was studied with the objective of developing statistical models, which give an indication of the probability of basic offender characteristics. Observable crime characteristics concerning the modus operandi, interaction between the offender and the victim, violence, precautionary measures, and sexual behaviours were selected in the dataset. Offender characteristics were selected based on their usefulness for the police organisation in narrowing the scope of a criminal investigation. Spatial behaviour, criminal history, and living situation of the offender were selected. From the predictive models, four out of five achieved a correct rate of over 70%, and all models predicted better than the best guess method. The proposed models for distance and prior convictions for violence seem particularly promising. Both these models show an improvement of correctly predicted offender characteristics of more than 20 percentile points compared with that which could have been estimated based on the average in the total sample. The predictive value of the models needs to be tested further with ‘new offences’, which were not used to construct the model. In general, the current study supports the finding that crime characteristics can be used to get an indication of the probability of certain offender characteristics. Nevertheless, for an understanding of the relationship between the crime characteristics and offender characteristics, a further development of a theoretical framework is urgently necessary. Copyright © 2009 John Wiley & Sons, Ltd.     

Exploring Directional Consistency in Offending: The Case of Residential Burglary in The Hague

Many aspects of human behaviour are remarkably stable across times, places and situations. Repetition and predictability also characterises our geographical behaviour. Prior research has confirmed that criminal behaviour is no exception. Offenders tend to recidivate, and recidivists tend to be behaviourally consistent in many aspects, including geographical ones. The present study assesses directional consistency in offending. It reviews the literature on directional consistency. It proposes an improved measure of directional consistency, and empirically uses this measure to explore directional consistency amongst a set of 268 burglars in The Hague. Copyright © 2012 John Wiley & Sons, Ltd.     

Linking serial residential burglary: comparing the utility of modus operandi behaviours,geographical proximity,and temporal proximity

Whilst case linkage is used with serious forms of serial crime (e.g. rape and murder), the potential exists for it to be used with volume crime. This study replicates and extends previous research on the behavioural linking of burglaries. One hundred and sixty solved residential burglaries were sampled from a British police force. From these, 80 linked crime pairs (committed by the same serial offender) and 80 unlinked crime pairs (committed by two different serial offenders) were created. Following the methodology used by previous researchers, the behavioural similarity, geographical proximity, and temporal proximity of linked crime pairs were compared with those of unlinked crime pairs. Geographical and temporal proximity possessed a high degree of predictive accuracy in distinguishing linked from unlinked pairs as assessed by logistic regression and receiver operating characteristic analyses. Comparatively, other traditional modus operandi behaviours showed less potential for linkage. Whilst personality psychology literature has suggested we might expect to find a relationship between temporal proximity and behavioural consistency, such a relationship was not observed. Copyright © 2010 John Wiley & Sons, Ltd.