Davies, Wittebrood, and Jackson (1997) were among the first to investigate whether offense behaviors are predictive of criminal history, with the findings of their paper then utilized by the National Crime Agency (NCA) Behavioral Investigative Advisors (BIAs) when assisting rape investigations. The aim of the study was to replicate this seminal paper with a larger contemporary sample of U.K. stranger rapists as identified by NCA. Data from 474 adult male stranger rapists were obtained in relation to 22 crime scene behaviors and nine preconviction variables. Results indicated significant differences between the Davies et al. original data set and this contemporary data set in both the behaviors and the preconvictions they displayed. The contemporary sample was significantly less likely to use sighting precautions, use violence, and take fingerprint precautions. This sample was also significantly less likely to have any of the preconviction crime types, with the exception of drugs offenses. When exploring the current data set of stranger rapists, statistical analyses indicated a number of key offense behaviors that were able to predict the criminal history of stranger rapists. However, contrary to previous research, no behaviors were found to be associated with sexual offense preconvictions. The results highlight that behaviors and characteristics of stranger sex offenders have changed since the 1990s. The implications for practice are discussed.

Purpose To conduct a test of the principles underpinning crime linkage (behavioural consistency and distinctiveness) with a sample more closely reflecting the volume and nature of sexual crimes with which practitioners work, and to assess whether solved series are characterized by greater behavioural similarity than unsolved series. Method A sample of 3,364 sexual crimes (including 668 series) was collated from five countries. For the first time, the sample included solved and unsolved but linked‐by‐DNA sexual offence series, as well as solved one‐off offences. All possible crime pairings in the data set were created, and the degree of similarity in crime scene behaviour shared by the crimes in each pair was quantified using Jaccard's coefficient. The ability to distinguish same‐offender and different‐offender pairs using similarity in crime scene behaviour was assessed using Receiver Operating Characteristic analysis. The relative amount of behavioural similarity and distinctiveness seen in solved and unsolved crime pairs was assessed. Results An Area Under the Curve of .86 was found, which represents an excellent level of discrimination accuracy. This decreased to .85 when using a data set that contained one‐off offences, and both one‐off offences and unsolved crime series. Discrimination accuracy also decreased when using a sample composed solely of unsolved but linked‐by‐DNA series (AUC = .79). Conclusions Crime linkage is practised by police forces globally, and its use in legal proceedings requires demonstration that its underlying principles are reliable. Support was found for its two underpinning principles with a more ecologically valid sample.

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 2 research must compare these methods in terms of accuracy, usability, and suitability for practice.

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