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Dragnet
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screenshotDragnet is a geographical prioritisation package. Using the locations of a series of crimes Dragnet will prioritise the surrounding areas in relation to the likely location of the offender's base. The use of the term prioritise is very important in this context. The end result of the Dragnet analysis is a map like the one to the right - Dragnet is not an 'X marks the spot' program.

Dragnet is the end result of a series of tests on offence series of serious serial offenders. The graph below shows across a sample of solved 79 US serial killers the percentage of the original search area that had to be searched before the home base of the offender was identified. It can be seen that for 87% of the sample the offenders home base was identified by searching up to 25% of the search area, for 51% of the sample a search area of only 5% was required. Moreover a search of only 1% of the original search area were required for 15% of the sample. Click here for a more detailed look at the development of Dragnet. Click here for details of the published work.


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In a real life situation the search costs would actually be smaller than those reported here because the Dragnet analysis works with abstract offence series maps containing only the locations of the crime scenes. Therefore areas such as parks and lakes will be included in the prioritised map even though the chances of the offender being based there are minimal. It is therefore at this stage that local investigating officers will contribute their valuable insight into the crime series and it's setting to provide a very powerful investigative support tool.

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The stages of the analysis

screenshotThe first stage is for the user to input the locations of the crimes. This produces an offence map like that to the right. Each of the black points on the map represents a crime scene, in this case each point is a body disposal location.

screenshotThe user then runs the analysis to produce a prioritised map similar to that on the right. The map is prioritised using the key:

key
High ................Low
... Prioritisation

screenshotThe actual formation of the map can indicate additional offence details such as the existence of more than one geographical focus present within the offences possibly indicating the existence of more than one offender. The map to the right shows the location of the home for this case.

screenshotDragnet also has features that will adjust the prioritisation pattern for city block networks. The diagram to the right shows a prioritised offence map that also incorporates structural axis produced by an analysis option within Dragnet. This option can be used to indicate any linear structuring that exists within an offence series. The results (the line) can then be used with local knowledge of transport networks and case specific information such as time of offence to produce proactive policing strategies.

The software is useful not only in an operational tool for the police but is also invaluable for research into offenders' offence site selection behaviours as well as for other human geographic practices. To order a copy of Dragnet click here alternatively if you have any further questions or comments then contact a specialist here.

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Purchasing Dragnet

If you would like to purchase Dragnet, please contact:
canter@liv.ac.uk



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References

The following is a selection of references relevant to the issues involved in the study of offenders' spatial behaviour. The first section includes publications from the Centre for Investigative Psychology, the second includes a further selection that introduce some of the basic concepts within the field.


Canter, D. & Larkin P. (1993).
The Environmental Range of Serial Rapists.
Journal of Environmental Psychology . 13: 63-69.


Canter, D.V. & Gregory, A. (1994)
Identifying the Residential Location of Rapists. Journal of the Forensic Science Society.
34, 3: 169-175.


Canter, D., Coffey, T., Huntley, M. & Missen, C. (in press).
Predicting Serial Killers Home Base Using a Decision Support System. Journal of Quantitative
Psychology.

Godwin, M. and Canter, D. (1997)
Encounter and Death: The Spatial Behaviour of U.S. Serial Killers. Policing: International Journal of Police Strategy and Management, vol.20, pp 24-38.

Hodge, S. & Canter, D.V. (1998).
Predatory Patterns of Serial Murderers. Centre for Investigative Psychology: Internal Report, submitted for publication.

Brantingham, P. J. & Brantingham P. L., Eds. (1981). Environmental Criminology. Sage, London, pp 27-54.

Fink, G. (1969).
Einsbruchstatorte vornehmlich an einfallstrassen? Kriminalistik. 23: 358-360.

Golledge, R. G. (1987).
Analytical Behavioural Geography. Croom Helm, London.

Kind, S.S. (1987).
Navigational Ideas and the Yorkshire Ripper Investigation. Journal of Navigation. 40, 3: 385-393.


Kocsis, R. N. & Irwin, H.J. (1997).
An Analysis of Spatial Patterns in Serial Rape, Arson, and Burglary: The Utility of the Circle Theory of Environmental Range for Psychological Profiling. Psychiatry, Psychology and Law. 4 , 2: 195-206.

Rengert, G. & Wasilchick, J. (1985).
Suburban Burglary. Charles C. Thomas, London.

Rhodes, W.M. & Conly, C. (1981).
Crime and Mobility: An Empirical Study. In: Brantingham, P.J. & Brantingham, P.L. Eds. Environmental Criminology: 167-188.

Rossmo, K. (1995).
Place, Space, and Police Investigations: Hunting Serial Violent Criminals. In: Eck, J.E. & Weisburd, D. Eds.
Crime and Place. Criminal Justice Press, NY, pp 217-235.

Tamura, M. & Suzuki, M. (1997).
Criminal Profiling Research on Serial Arson: Examination of Circle Hypothesis Estimating Offender's Residential Area. In: Reports of the National Research Institute
of Police Science. Research on Prevention of Crime & Delinquency July. 38, 1.


Turner, S. (1969).
Delinquency and Distance. In: Wolfgang ME and Sellin T, (eds.). Delinquency: Selected Studies. John Wiley, New
York.


Warren, J., Reboussin, R. and Hazelwood, R. R. (1995).
The Geographic and Temporal Sequencing of Serial Rape. Final Report submitted
to the National Institute of Justice July 15th 1995.




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Books
David Canter's book, Criminal Shadows. Re-printed for the American Market
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Books
Social Psychology of Crime, Edited by David Canter & Laurence Alison
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Books
Profiling in Policy and Practice -
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Reading IP
Reading Material for the field of Investigative Psychology
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