Linking serial sexual offences: moving towards an ecologically valid test of the principles of crime linkage

Jessica Woodhams, Matthew Tonkin, Hanne Imre, Jan M. Winter, Eva Lam, Gert-Jan ten Brinke, Mark Webb, Gerard Labuschagne, Craig Bennell, Leah Ashmore-Hills, Jasper van der Kemp, Sami Lipponen, Tom Pakkanen, Lee Rainbow, C. Gabrielle Salfati, Pekka Santtila, Amy Burrell

Research output: Contribution to journalArticlepeer-review

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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.
Original languageEnglish
Pages (from-to)123-140
Number of pages18
JournalLegal and Criminological Psychology
Issue number1
Early online date15 Dec 2018
Publication statusPublished - Feb 2019


  • assumptions
  • comparative case analysis
  • linkage analysis
  • case linkage
  • behavioural linking


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