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Assumptions Underlying Behavioural Linkage Revisited: Ascertaining Individual Differentiation and Consistency in Serial Rape
... Of the 6 serial homicide and 13 sexual offense studies on linking mentioned above, only 4 of the studies on serial homicide (Bateman & Salfati, 2007;Salfati & Bateman, 2005;Sorochinski & Salfati, 2010) and 2 of the studies on sexual assault (Kearns et al., 2011;Sorochinski & Salfati, 2017) specifically looked at the issue of behavioral consistency. ...
... Results therefore suggest again that thematic stability or instability across the series may be due to the type of victim targeted, and the question remains whether identifiable patterns may be determined based on these changing features as the series develops. Sorochinski and Salfati (2017) in an analysis of 30 series of sexual assault and rape showed that the control (including verbal control, control by using constraints such as binding and gagging, and control through using a weapon, and control through physical violence) and violent (at the start, during the offense, and at the end, and using manual violence and/or using a weapon) behavior subtypes could best understood quantitatively (i.e. in terms of the degree of the behavior employed), whilst the sexual activity (ranging from foreplay, to penetration, to demanding victim participation, and verbal sexual activity) was most usefully understood qualitatively in terms of the specific subtype exhibited. The analysis of consistency and behavioral trajectories showed that whilst none of the offenders exhibited complete consistency across the 3 behavioral subtypes, a subsample of offenders remained fully consistent in at least one. ...
... Analysis reveals that this component of offending may remain more stable than other variables (Deslauriers-Varin & Beauregard, 2013). All of these studies assume that at least some aspects of a perpetrator's offending pattern remain stable enough across incidents to distinguish crimes committed by that individual from similar crimes committed by others, such as the level of sexual intrusiveness, the presence or type of weapon used, or even whether a trajectory pattern can be detected (cf. Sorochinski, 2015). ...
... Kleban, Chesin, Jeglic, and Mercado (2013) compiled a number of other studies and also found evidence for crossover by gender, age, and relationship. Sorochinski (2015) attempted to determine whether offenders remained consistent in their behaviors or at least stuck to an identifiable trajectory and discovered that none remained completely stable, although a subset remained fully consistent in at least one behavior pattern. Lussier et al. (2008) created a more nuanced schema to understand offending patterns by differentiating between offenders who assaulted strangers, familial, and nonfamilial victims (i.e., victims they were not related to). ...
Purpose
Much of what we know about serial sex offenders is based on multiple sexual assaults linked via conviction or self-report or offenders who primarily target strangers. Our data are derived from serial sex offenders linked via DNA testing of unsubmitted sexual assault kits—which provides a more objective examination of offending patterns.
Methods
Study uses descriptive statistics, chi-square tests, and sexual assault narratives to explore offending patterns for serial vs. nonserial sex offenders and crossover offending patterns by relationship, age, and gender for serial sex offenders. We examine crossover offending patterns for three groups of serial sex offenders: those who assaulted only strangers, both strangers and nonstrangers, and only nonstrangers.
Results
Findings show significant crossover offending by relationship and age. Over one-quarter sexually assaulted both strangers and nonstrangers. Serial sex offenders often vary their offending pattern across offenses. The offender-victim relationship appears particularly salient when assessing offending patterns.
Conclusions
Offending patterns are not a consistently reliable link across assaults. Many of these sexual assaults had not been linked prior to DNA testing, thereby illustrating the power of the DNA testing of SAKs for identifying and linking serial sex offenders, particularly when testing is followed by a thorough investigation.
In recent years, a new type of interpersonal crime has emerged where victimization happens through the use of technology and/or cyber space. The legal, law enforcement, as well as social scientific research fields have yet to fully grasp the scope of this modern crime type. In this paper, we review what is currently known on the issue with 5 Ws and 1 H approach, in terms of their current understanding, prevalence, victimization patterns, motivations, and relationship between violence in the cyberspace and offline. We end with a proposal for future directions and argue that a useful framework for researching this type of crime may be the interpersonal model first developed within the investigative psychology field for the classification and profiling of sexually violent offenses.
Cambridge Core - Social Psychology - The Cambridge Handbook of Violent Behavior and Aggression - edited by Alexander T. Vazsonyi
Classification is a fundamental cognitive operation. From the first perceptual contact with stimuli (Pomerantz, 1986; Treisman, 1986) through the ultimate integration and storage of information in long-term memory (Rosch & Lloyd, 1978), the identification, organization, and integration of elements that share common characteristics has been shown to be an essential component of perception and cognition. The critical function of classification in scientific investigation mirrors its central role in general cognition. Phenomenalists, realists, and con-ceptualists, despite their diverse metaphysical perspectives, all recognize the vital role of classification in science (Ghiselin, 1981). It stands as a necessary precursor and pervasive sustainer of all scientific progress (Hempel, 1965).
Case linkage uses crime scene behaviours to identify series of crimes committed by the same offender. This paper tests the underlying assumptions of case linkage (behavioural consistency and behavioural distinctiveness) by comparing the behavioural similarity of linked pairs of offences (i.e. two offences committed by the same offender) with the behavioural similarity of unlinked pairs of offences (i.e. two offences committed by different offenders). It is hypothesised that linked pairs will be more behaviourally similar than unlinked pairs thereby providing evidence for the two assumptions. The current research uses logistic regression and receiver operating characteristic analyses to explore which behaviours can be used to reliably link personal robbery offences using a sample of 166 solved offences committed by 83 offenders. The method of generating unlinked pairs is then refined to reflect how the police work at a local level, and the success of predictive factors re‐tested. Both phases of the research provide evidence of behavioural consistency and behavioural distinctiveness with linked pairs displaying more similarity than unlinked pairs across a range of behavioural domains. Inter‐crime distance and target selection emerge as the most useful linkage factors with promising results also found for temporal proximity and control. No evidence was found to indicate that the property stolen is useful for linkage. Copyright © 2012 John Wiley & Sons, Ltd.
Much previous research on behavioural case linkage has used binary logistic regression to build predictive models that can discriminate between linked and unlinked offences. However, classification tree analysis has recently been proposed as a potential alternative owing to its ability to build user‐friendly and transparent predictive models. Building on previous research, the current study compares the relative ability of logistic regression analysis and classification tree analysis to construct predictive models for the purposes of case linkage. Two samples are utilised in this study: a sample of 376 serial car thefts committed in the UK and a sample of 160 serial residential burglaries committed in Finland. In both datasets, logistic regression and classification tree models achieve comparable levels of discrimination accuracy, but the classification tree models demonstrate problems in terms of reliability or usability that the logistic regression models do not. These findings suggest that future research is needed before classification tree analysis can be considered a viable alternative to logistic regression in behavioural case linkage. Copyright © 2012 John Wiley & Sons, Ltd.
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.
Purpose. The current study tests whether existing behavioural case linkage findings from the United Kingdom (UK) will replicate abroad with a sample of residential burglaries committed in Finland. In addition, a previously discussed methodological issue is empirically explored.
Methods. Seven measures of behavioural similarity, geographical proximity, and temporal proximity are calculated for pairs of burglary crimes committed by 117 serial burglars in Finland. The ability of these seven measures to distinguish between pairs of crimes committed by the same offender (linked pairs) and different offenders (unlinked pairs) is tested using logistic regression and receiver operating characteristic (ROC) analysis. Two methodologies for forming the unlinked pairs are compared; one representing the ‘traditional’ approach used by research and, the other, a new approach that represents a potentially more realistic and statistically sound approach to testing case linkage.
Results. A wider range of offender behaviours were able to distinguish between linked and unlinked crime pairs in the current Finnish sample than in previous UK-based research. The most successful features were the kilometre-distance between crimes (the intercrime distance), the number of days separating offences (temporal proximity), and a combination of target, entry, internal, and property behaviours (the combined domain). There were no statistically significant differences between the two methodological approaches.
Conclusions. The current findings demonstrate that a wider range of offender behaviours can be used to discriminate between linked and unlinked residential burglary crimes committed in Finland than in the UK. The use of a more realistic and statistically sound methodology does not lead to substantial changes in case linkage findings.
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.
Purpose. This paper is concerned with case linkage, a form of behavioural analysis used to identify crimes committed by the same offender, through their behavioural similarity. Whilst widely practised, relatively little has been published on the process of linking crimes. This review aims to draw together diverse published studies by outlining what the process involves, critically examining its underlying psychological assumptions and reviewing the empirical research conducted on its viability.Methods. Literature searches were completed on the electronic databases, PsychInfo and Criminal Justice Abstracts, to identify theoretical and empirical papers relating to the practice of linking crimes and to behavioural consistency.Results. The available research gives some support to the assumption of consistency in criminals' behaviour. It also suggests that in comparison with intra-individual variation in behaviour, inter-individual variation is sufficient for the offences of one offender to be distinguished from those of other offenders. Thus, the two fundamental assumptions underlying the practice of linking crimes, behavioural consistency and inter-individual variation, are supported. However, not all behaviours show the same degree of consistency, with behaviours that are less situation-dependent, and hence more offender-initiated, showing greater consistency.Conclusions. The limited research regarding linking offenders' crimes appears promising at both a theoretical and an empirical level. There is a clear need, however, for replication studies and for research with various types of crime.
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.
This study explores the role of the victim–offender relationship in the dynamics of homicide, by examining the crime scene behaviour of 25 intrafamilial, 30 acquaintance and 27 stranger homicide offenders (n = 82). Six crime scene variables were examined: ‘Weapon from the scene’, ‘Excessive wounding’, ‘Facial trauma’, ‘Multiple wounds to a single area’, ‘Post-mortem activity’ and ‘Manual violence’. The first objective was to identify whether these variables could be combined to form a partially ordered scale of expressiveness. The second was to examine whether the nature of this expressive crime scene varied according to the victim and offender relationship. It was hypothesised that the intrafamilial homicides would be characterised by a more expressive crime scene. This was examined by Partial Order Scalogram Analysis which supported the hypothesised link between the level of expressed emotion evident in the crime scene and the nature of the victim–offender relationship. Further analysis on the individual variables revealed that the best single predictor of the relationship between victim and offender was the presence of multiple wounding. These findings are discussed both as contributing to a theoretical understanding of the emotional salience of crime scene actions when killing a family member, and in practical terms in relation to the significance of these variables for both police investigations and clinical interventions with homicide perpetrators.
The present study investigated the possibility of statistically linking arson cases based on consistency of behaviors from one crime scene to another. Serial and spree arson cases were studied to differentiate underlying themes and to link cases committed by the same offender. The material consisted of 248 arson cases which formed 42 series of arsons. A content analysis using 45 dichotomous variables was carried out and principal components (PCA) analysis was performed to identify underlying themes. Summary scores reflecting the themes were calculated. Linking effectiveness was tested with a discriminant analysis using the summary scores. The PCA analysis was successful and underlying themes which were in accordance with previous studies could be identified. Six factors were retained, in the PCA. The linking of the arson cases was possible to a satisfactory level: 33% of the cases could be correctly linked and for over 50% of the cases, the series they actually belonged to was among the ten series identified as most probable on the basis of the linking analysis. From a practical point of view, the results could be used as a basis for developing support systems for police investigations of arson. © Copyright Springer, 2004
It is hypothesized that stranger rape victim statements will reveal a scale of violation experienced by the victim, ranging from personal violation, through to physical violation, and finally, at the most extreme level, sexual violation. It is also hypothesized that offences can be differentiated in terms of one of four themes: hostile, controlling, stealing, or involving. To test these hypotheses, crime scene data from 112 rapes were analyzed by the multi-dimensional scaling procedure Smallest Space Analysis. The results provide empirical support for a composite model of rape consisting of four behavioral themes as different expressions of various intensities of violation. The results also suggest that stranger rapes may be less about power and control than about hostility and pseudo-intimacy. The proposed model has implications for the classification of rape, the investigation of sexual crimes, and the treatment of victims.
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
When relying on crime scene behaviours to link serial crimes, linking accuracy may be influenced by the measure used to assess across-crime similarity and the types of behaviours included in the analysis. To examine these issues, the present study compared the level of linking accuracy achieved by using the simple matching index (S) to that of the commonly used Jaccard's coefficient (J) across themes of arson behaviour. The data consisted of 42 crime scene behaviours, separated into three behavioural themes, which were exhibited by 37 offenders across 114 solved arsons. The results of logistic regression and receiver op-erating characteristic analysis indicate that, with the exception of one theme where S was more effective than J at discriminating between linked and unlinked crimes, no significant differences emerged between the two similarity measures. In addition, our results suggest that thematically unrelated behaviours can be used to link crimes with the same degree of accuracy as thematic-ally related behaviours, potentially calling into the question the importance of theme-based approaches to behavioural linkage analysis.
Cette étude s'est proposé; d'explorer la structure de profils multivariés issus d'une partie des items de la Suicide Probability Scale (Cull & Gill, 1982). L'analyse du scalogramme partiellement ordonné, une extension multi-dimensionnelle de la traditionnelle échelle de Guttman, a été exploitée pour l'étude des profils. L'échantillon était constitué de sujets suicidaires (n= 35) et non suicidaires, ceux-ci étant tirés de populations normale (n= 35) et psychiatrique (n= 30). La structure partiellement ordonnée des profils renvoya à un espace bidimensionnel, ce qui signifiait que l'information contenue dans un profil multivarié pouvait être résumée par deux axes procédant de la structure partiellement ordonnée. Les coordonnées correspondaient au rang de chaque profil sur des items appréciant les expressions cognitive et affective de l'adaptation psychologique. L'espace bidimensionnel differencial clairement les suicidaires des autres, les profils des premiers étant bien plus hétérogènes. Les analyses ont montré que le suicide n'était pas un phénomène unitaire.
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.
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.
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.
The purpose of the present study is to test the case linkage principles of behavioural consistency and behavioural distinctiveness using serial vehicle theft data. Data from 386 solved vehicle thefts committed by 193 offenders were analysed using Jaccard's, regression and Receiver Operating Characteristic analyses to determine whether objectively observable aspects of crime scene behaviour could be used to distinguish crimes committed by the same offender from those committed by different offenders. The findings indicate that spatial behaviour, specifically the distance between theft locations and between dump locations, is a highly consistent and distinctive aspect of vehicle theft behaviour; thus, intercrime and interdump distance represent the most useful aspects of vehicle theft for the purpose of case linkage analysis. The findings have theoretical and practical implications for understanding of criminal behaviour and for the development of decision-support tools to assist police investigation and apprehension of serial vehicle theft offenders.
Establishing behavioral consistency in serial homicide offending behavior is essential when linking homicides together and to a common offender. An examination of 35 serial homicide behaviors utilized by 90 offenders in 450 serial homicide cases was carried out to identify whether these offenders consistently performed the same behaviors across their series of homicides and whether it is more effective to examine individual behaviors or groupings of behaviors in order to identify behavioral consistency. This study provides the first empirically based evidence testing the use of using single behaviors as linking factors in linking homicide cases in a series, and shows that this method has inherent difficulties in accomplishing this, thus providing the first wave of empirical testing that questions current theories in the literature on serial homicide, which has suggested that signatures or specific key behaviors are important in understanding the consistency in an offender's behavior across the crimes. Recommendations for future studies on linking using signatures are suggested, including a more in-depth qualitative empirical evaluation of individual series.