Dragnet 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.
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.
The stages of the analysis:
The 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.
The user then runs the analysis to produce a prioritised map similar to that on the right. The map is prioritised using the key:
The 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.
Dragnet 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.
If you would like to purchase Dragnet, please contact: email@example.com