Abstract
Purpose: The aims of the present project were (1) to describe the typical travel distances from home to offence locations (journey-to-crime) of offenders in difficult-to-solve homicides and rapes as well as residential burglaries and commercial robberies; (2) to see whether the travel distances in these offences differ from each other in the different countries participating in the research; (3) to test whether selected features related to the offence and, as a rule, available to the police in the beginning of the offence investigation would be associated with the travelling distances of the offenders. The overall aim of the research was to provide information concerning typical travel distances of offenders that could be used to prioritise a search area in which an offender is likely to live in new unsolved offences. Method: Lists of difficult-to-solve (DTS) homicides and rapes as well residential burglaries and commercial robberies were prepared after which representative samples of these were selected for further analysis. The collected data consisted of journey-to-crime coordinates together with information on the crime scene behaviour of the offenders in solved offences for which the offender's residence or regular domicile address was known. The journey-to-crime function for each was estimated using the journey-to-crime module of CrimeStat©. When estimating the Jtc-function, the following parameters were used for all the crimes: The function presented probabilities of crime incident happening on a certain distance from home. Estimation was made using a normally distributed kernel with a fixed bandwidth and distance bin of 5oo meters. Output units used were kilometres. Association between the presence of a particular crime scene behaviour and the median journey-to-crime distance were explored using Mann-Whitney U tests. Results: The spatial behaviour of offenders followed the same general pattern in the different countries: most of the journeys-to-crime were on the short side followed by a minority of longer journeys. the distance decay function as a valid model of offender spatial behaviour received strong support. There were clear differences in median journey-to-crime trips between expressive (homicide and rape) and (robbery and burglary) offences. The median journey-to-crime distances travelled in expressive offence types were much shorter than those travelled to instrumental crime locations: Homicide journey-to-crime median distances were below 1 km, rape journey-to-crime median distances were below 2.5 km whereas residential burglary and commercial robbery median journey-to-crime distances were over 4 km in all countries. It was possible to identify crime features that were statistically significantly correlated with the journey-to-crime distance the offender had travelled for each of the offence types and in each of the countries included in the present study. Conclusions: The results have important practical implications for police crime investigations as the crime feature explored in the present study were, as a rule, such that they would be known by the police prior to the offender having been identified in any way. What is needed is a general theoretical framework for binding together journey-to-crime distances and offender crime scene behaviour and other important crime features. It is also important to try to identify theoretical constructs for understanding the links between different crime feature instead of looking at them in isolation. the travel patterns of offenders should be studied be separately in different countries and one should be wary of generalising findings from one context or country too hastily to another one.