Police investigators are often faced with the challenge of linking serial crimes. In ideal situations, linkage decisions will be based on physical evidence left at crime scenes. However, in the absence of such evidence, investigators must rely on behavioural clues to make these decisions on whether two (or more) crimes have been perpetrated by the same offender – commonly known as crime linkage analysis (CLA).
The goal of CLA is to identify patterns of behaviour that meet two criteria: behavioural stability and behavioural distinctiveness (Bennell et al., 2009). Behavioural stability exists when offenders behave in the same or similar way across their crime series. Behavioural distinctiveness exists when the behaviors exhibited by serial offenders differ from one another. When offenders behave in a relatively stable and distinct fashion, it should be possible to link offenders to the crimes they have committed and to differentiate between the crimes committed by different offenders. To accomplish this, a threshold must usually be set to determine when crimes are similar (or different) enough to warrant a linkage decision (or not) being made.
Much of the research conducted on behavioural linkage analysis to date has tested the assumptions of behavioural stability and distinctiveness. A point has now been reached where researchers can be confident that behavioural linkage analysis is indeed possible, at least to a moderate degree (Bennell et al., 2013).
How we can help
Several members of our group have expertise in case linkage analysis. We can provide detailed analysis on the potentiality of one or more crimes linked to one or more series of offences. An investigative decision tree-framework can be utilised to support investigator knowledge and experience in the CLA assessment and analysis. An empirical basis for linking (or not linking) crimes will also be provided giving security (e.g., justification and clarity) and objectivity (e.g., evidence-based) to decisions made by the investigative team.