other instances a nonuniform target backcloth may force a commuter pattern regardless of the offender’s hunting style.

As part of a suggested taxonomy of rape series, Alston (1994) proposes marauders be defined as those offenders who consistently travel under 5 kilometres from a primary activity site (e.g., home or work) to the initial victim contact scene, and commuters as those who travel more than 5 kilometres. He observes the latter tend to stay close to the major thoroughfares used for their crime journeys. Davies and Dale (1995b) caution “that the commuter and marauder models may just be extremes of a continuum of patterns determined by topography and target availability” (p. 16).

9.2 Geography of Serial Murder

Descriptive accounts of serial murder and rape spatial patterns are useful, but a greater understanding of offender behaviour is gained by applying theories and techniques from environmental criminology and quantitative geography (Brantingham & Brantingham, 1984; R. V. Clarke, 1992, 1997; Garson & Biggs, 1992; Taylor, 1977). To this end, a seven-year research project on geographic profiling and target patterns of serial murderers was conducted at Simon Fraser University’s (SFU) School of Criminology (Rossmo, 1995a). The study involved the collection and analysis of two forms of data: (1) macrolevel information on serial killers; and (2) microlevel information on offenders, victims, and locations for selected serial murders.

Within a geography of crime perspective, locations of crime sites are seen to be influenced by hunting style, target backcloth, and changes in offender activity space. Some of the related questions this study sought to answer include: (1) which crime location types, individually or jointly, are the best predictors of offender residence; (2) what do the characteristics of the crime site and surrounding area tell us about the offender; and (3) is it possible earlier crimes, committed before the killer gained experience and expanded his or her spatial repertoire, are better indicators of an offender’s home area? The SFU serial murder data set provided the information necessary for an analysis concerned with these and other issues. Area and neighbourhood characteristics, victim types and activities, date and time periods, and offender mobility were examined. Data were also available to compute crime trip distances, size of hunting area, degree of pattern aggregation, and weekday of offence.

49 The probability that n crimes of a marauder will appear to be those of a commuter is approximately: (2n – 1)/(22n – 2). The likelihood such a pattern could happen by chance is not insignificant for low values of n. For example, in a series of 4 crimes the probability is equal to 0.23.

© 2000 by CRC Press LLC