The utility of the Violent Crime Linkage Analysis System for conducting comparative case analysis

Purpose The Violent Crime Linkage Analysis System (ViCLAS) is a computerised database which is used by law enforcement in several countries to find potential links between serial violent crimes. In 2012, Bennell, Snook, MacDonald, House and Taylor identified a number of assumptions that must be valid for these computerised systems to be effective. Design/methodology/approach This paper revisits and expands on these assumptions with specific reference to the use of ViCLAS, looking at research that has been conducted since this 2012 review and outlining where research is still outstanding. Findings The importance of evaluating ViCLAS is highlighted in this paper. Practical implications Particularly, the research agenda highlights how the practice of comparative case analysis when using ViCLAS could be improved. Originality/value To the best of the authors’ knowledge, this is the first review of the research dedicated specifically to the evaluation of ViCLAS.

Crime linkage practice in New Zealand

Purpose The purpose of this paper is to understand (i) how crime linkage is currently performed with residential burglaries in New Zealand, (ii) the factors that promote/hinder accurate crime linkage and (iii)whether computerised decision-support tools might assist crime linkage practice. Design/methodology/approach A total of 39 New Zealand Police staff completed a questionnaire/interview/focus group relating to the process, challenges, products and uses of crime linkage with residential burglary in New Zealand. These data (alongside four redacted crime linkage reports) were subjected to thematic analysis. Findings The data clearly indicated wide variation in crime linkage process, methods and products (Theme 1). Furthermore, a number of factors were identified that impacted on crime linkage practice (Theme 2). Research limitations/implications Future research should develop computerised crime linkage decision-support tools and evaluate their ability to enhance crime linkage practice. Also, researchers should explore the use of crime linkage in court proceedings. Practical implications To overcome the barriers identified in the current study, greater training in and understanding of crime linkage is needed. Moreover, efforts to enhance the quality of crime data recorded by the police will only serve to enhance crime linkage practice. Social implications By enhancing crime linkage practice, opportunities to reduce crime, protect the public and deliver justice for victims will be maximised. Originality/value The practice of crime linkage is under-researched, which makes it difficult to determine if/how existing empirical research can be used to support ongoing police investigations. The current project fills that gap by providing a national overview of crime linkage practice in New Zealand, a country where crime linkage is regularly conducted by the police, but no published linkage research exists.

Closer to reality? The application of sequence analysis in crime linkage

Purpose Traditional crime linkage studies on serial sexual assaults have relied predominantly on a binary crime linkage approach that has yielded successful results in terms of linkage accuracy. Such an approach is a coarse reflection of reality by focussing mainly on the outcome of an offence, neglecting the forceful differences due to the intricate offender-victim interaction. Only few researchers have examined sexual assaults through the lens of a sequence analysis framework. This paper aims to present the first empirical test of offence sequence-based crime linkage, moving beyond exploratory analyses. Design/methodology/approach Offence accounts from 90 serial sexual assault and rape victims from the UK were analysed and sequentially coded. Sequence analysis allowed to compare all offences combinations regarding their underlying sequence of events. The resulting comparison was transformed and plotted in two-dimensional space by multidimensional scaling analysis for a visual inspection of linkage potential. The transformed proximities of all offences were used as predictors in a receiver operating characteristic analysis to actually test their discriminatory accuracy for crime linkage purpose. Findings Sequence analysis shows significant discriminatory accuracy for crime linkage purpose. However, the method does perform less well than previous binary crime linkage studies. Research limitations/implications Several limitations due to the nature of the data will be discussed. Practical implications The practical limitations are as follows: the study is a potential practical value for crime analysts; it is a complimentary methodology for statistical crime linkage packages; it requires automated coding to be useful; and it is very dependent on crime recoding standards. Originality/value The exploratory part of this study has been published in a book chapter in 2015. However, to the best of the authors’ knowledge, the succinct test of crime linkage accuracy is the first of its kind.

Linking serial homicide – towards an ecologically valid application

Purpose Crime linkage analysis (CLA) can be applied in the police investigation-phase to sift through a database to find behaviorally similar cases to the one under investigation and in the trial-phase to try to prove that the perpetrator of two or more offences is the same, by showing similarity and distinctiveness in the offences. Lately, research has moved toward more naturalistic settings, analyzing data sets that are as similar to actual crime databases as possible. One such step has been to include one-off offences in the data sets, but this has not yet been done with homicide. The purpose of this paper is to investigate how linking accuracy of serial homicide is affected as a function of added hard-to-solve one-off offences. Design/methodology/approach A sample (N = 117–1160) of Italian serial homicides (n = 116) and hard-to-solve one-off homicides (n = 1–1044, simulated from 45 cases) was analyzed using a Bayesian approach to identify series membership, and a case by case comparison of similarity using Jaccard’s coefficient. Linking accuracy was evaluated using receiver operating characteristics and by examining the sensitivity and specificity of the model. Findings After an initial dip in linking accuracy (as measured by the AUC), the accuracy increased as more one-offs were added to the data. While adding one-offs made it easier to identify correct series (increased sensitivity), there was an increase in false positives (decreased specificity) in the linkage decisions. When rank ordering cases according to similarity, linkage accuracy was affected negatively as a function of added non-serial cases. Practical implications While using a more natural data set, in terms of adding a significant portion of non-serial homicides into the mix, does introduce error into the linkage decision, the authors conclude that taken overall, the findings still support the validity of CLA in practice. Originality/value This is the first crime linkage study on homicide to investigate how linking accuracy is affected as a function of non-serial cases being introduced into the data.

Behavioural Crime Linkage in Rape and Sexual Assault Cases

Behavioural crime linkage (BCL) analyses offender crime scene behaviour with the aim of identifying groups of crimes that share similar (and distinctive) behaviours. This allows police to infer that the same person/s were responsible for crimes, allowing them to be “linked” as a crime series. Successful BCL can increase the quantity and quality of evidence available to the police, which increase the likelihood of apprehending and successfully prosecuting the offender. This chapter will review the theoretical framework underpinning BCL (behavioural consistency and behavioural distinctiveness) and summarise key literature on rape and sexual assault - including the latest, cutting-edge, collaborative work jointly-led by academics and law enforcement practitioners. The chapter will also outline (using real life case studies) how BCL can be used to support the investigation of sexual offences, and will critically discuss future research directions and how this work might enhance the detection, prosecution, and prevention of serial sexual offending.