Environmental consistency and spatial differentiation: the role of the environment and spatial patterns in the offence site location choice of serial sex offenders

Abstract

The present study examines the spatial behaviour of serial sexual offenders in New Zealand. Spatial and contextual information pertaining to the offender, victim and offence was collected from police case files. The resulting sample consisted of 76 offenders who had committed at least two sexual offences with at least one sexual violation between the years of 1970 and 2002 inclusive. All offenders were male, and all victims were female. The initial aim of the study was to conduct a descriptive analysis of the offenders’ spatial behaviour. In line with much previous, overseas research, it was found that typically, offenders were not traveling very far from home to commit their offences with a median distance of 3.08km. An examination of the spatial patterns exhibited by offenders found support for the marauder/commuter distinction as put forward by Canter and Larkin (1993). In contrast to previous studies however, it was found that instead of the marauding pattern occurring most frequently, both patterns occurred in equal numbers. Furthermore, it was found that a significant proportion of the offenders were unclassifiable due to the transient nature of their offending. An initial examination of the distances travelled by the offenders was also carried out in order to examine how consistent they were in terms of their spatial behaviour across their series. Support was found for spatial consistency. The second aim was to further the notion of consistency and investigate whether there was evidence for a broader environmental consistency in offence site selection. In order to do this, a consistency measure made up of eight physical, temporal, and contextual environmental variables was developed and compared across each offender's series. Support was found for the notion of environmental consistency with offenders displaying intra-series consistency in their offence site selection over and above what would be expected by chance. Support was also found for environmental consistency between offender home base and crime site locations. Having established that the offenders tend to be both spatially and environmentally consistent in their crime site selection choices, it was hypothesized that it would be possible to differentiate between offenders in terms of such spatial and environmental behaviour. In particular, it was hypothesized that differences in behaviour would be found according to whether the offender was a marauder, commuter or transient. Multiple discriminate analysis was carried out in order to investigate this possibility, results showed that all three groups could be differentiated according to a number of environmental variables. Contextual, temporal and physical environmental variables contributed to the discriminant function. The current research examined the spatial behaviour of serial sex offenders and found that they exhibit consistency in both the spatial and environmental features of their crime site selection choice. Furthermore, it was demonstrated that offenders who differ in terms of the spatial pattern they exhibit, also differ in terms of other environmental features of their offending. These findings have important implications for both psychological modelling of offender spatial behaviour and the applied field of geographic profiling. In line with previous research in the field of environmental criminology, the present study highlights the importance of examining the spatial and environmental context of offending.