Behavioural Consistency and Offender Characteristics: Investigating Modus Operandi Patterns in Serial Stranger Sex Offences

Case linkage is a statistical technique which connects multiple sexual assault cases to a single perpetrator and holds promise for informing criminal investigations. Further, examining the behaviours executed most consistently across serial offences committed by a given offender is crucial to linking offences. The current study investigated behavioural consistency in a sample of 49 male serial stranger sexual offenders responsible for 147 offences. For each offence, four crime aspects were identified: 1) pre-crime facilitators, 2) victim selection and characteristics, 3) approach and attack methods, and 4) crime scene characteristics. Consistency between and within each crime series and across offender types based on background characteristics was examined. Results indicated a high degree of behavioural consistency across all crime aspects. Behaviours occurring prior to the offence were particularly useful in establishing consistent offending patterns. The implications of these findings in the context of police investigations and their utility for clinical practice are discussed.