Geographical profiling in a novel context: prioritising the search for New Zealand sex offfenders

Abstract

The present work explores the utility and value of geographical offender profiling methodologies within a novel context, considering both theoretical and practical issues relating to their application. The effectiveness of a well-known geographical profiling system, Dragnet, was tested across 101 New Zealand sex offence series, and findings compared with those derived for an equivalent sample from the UK. Average search costs (the amount of the total offence area that needed to be searched, starting from predicted offender home location, before the offender's actual home was reached) were far greater for the New Zealand sample than their UK offending counterparts. It is argued that this is because the spatial behaviour of New Zealand offenders violates many of the assumptions that Dragnet and other similar geographical profiling systems make in predicting offenders' home locations. Calibration of the system to the specific home-crime distance patterns of the New Zealand offenders did not enhance the efficacy of predictions made to a significant extent. It is consequently argued that, in their current form, geographical profiling systems are limited in their ability to account for samples displaying very different spatial characteristics to those that they were developed from and for. The implications of these findings for the general utility of geographical profiling are discussed, and ways in which systems might be developed in order to broaden their scope and applicability are suggested.

Keywords:

• geographical profiling
• sex offences
• journey-to-crime
• Dragnet

Acknowledgements

This project was the result of an overseas institutional research visit funded by the Economic and Social Research Council as part of the author's doctoral research programme. The New Zealand Police Criminal Profiling Unit acted as a host, and provided access to archival data on convicted sex offenders which was used to gain the geographical information necessary for the analyses presented.

Without a number of people this project would not have taken place, and they deserve a great deal of recognition and thanks. Firstly, thanks you to the members of the New Zealand Police Criminal Profiling Unit, to Mary Goddard for helping to set this all up, to Brett Pakenham, David Scott, and particularly to Russell Lamb for his endless assistance in compiling the sample and data. Thanks you to the New Zealand Police for acting as a host institution, and to the RESC for permitting the work to take place. A special thank you to Rebecca Morton and the ESRC for the award enabling the project, and last, but by certainly no means least, I'd like to say thank you to Professor David Canter for all of his help in the preparation of this article and in the project itself, as well as for his constant supervision and support. It is greatly appreciated.

I would also like to thank two anonymous reviewers and the editor of this journal for their helpful comments and feedback on earlier versions of this work.

Notes

1. For more information on the Dragnet system or to obtain a copy of the latest version, contact Laura Hammond at the IRCIP ([email protected]) or visit www.ia-ip.org.