Linking personal robbery offences using offender behaviour

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.