9.2.1Methodology

9.2.1.1Serial Killer Data

The first database (henceforth referred to as the FBI serial killer data set) contains macrolevel information on serial killers. The main source for this data was an FBI NCAVC Lexus/Nexus newspaper computerized topical search file on serial murderers in the U.S. The crimes are therefore primarily, though not exclusively, North American. An attempt was made to clean and verify the information in the original list, and to eliminate those cases that are closer to a spree or mass murder classification. To this end, the FBI definition of serial murder was used (see Ressler et al., 1988). While there was no attempt to be comprehensive, an effort was made to update the data and include wellknown foreign serial killers. The final list consists of 225 cases, including most well-known serial killers. Information in the FBI serial killer data set includes: (1) offender name; (2) moniker or media name; (3) sex; (4) associates; (5) number of confirmed victims; (6) number of suspected victims;

(7) start date of murders; (8) end date of murders; and (9) cities, states or provinces, and countries of operation.

The data set on serial killers served two analytic purposes. First, it was the means by which frequencies, averages, and rates were computed for the macrolevel variables. Regional variation in serial murder was also examined through state comparisons of counts and rates (adjusted for both population and overall murder). Second, this list was the source for the microlevel serial murder data set. One of the critical elements of the selection criteria involved choosing those cases where the serial murderer’s activity space and hunting style produced target patterns that are amenable to geographic profiling. This ultimately led to the development of the predator hunting typology, a necessary step in the articulation of the applicability and limits of geographic profiling. The larger data set made this process feasible.

9.2.1.2Newspaper Sources

While the use of newspaper data in serial murder research is common, a few cautions are worth noting. Egger (1990) states that “it would appear that the mass media are currently the only source from which to quantify serial murders in this country [U.S.]” (p. 11). He searched The New York Times Index from January 1978 to June 1983 for cases of serial killers (1984, 1990). Simonetti (1984) perused the same index and associated microfilm files for stories of serial murder cases from January 1970 to November 1983. Jenkins (1988a, 1989) researched newspaper archives, including The New York Times Index, to compile a list of major cases of serial murder in the U.S. from 1900 to the present, finding just as much journalistic interest in this topic in the early part of the century as in the later.

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Levin and Fox (1985) searched indices of six major American newspapers for serial and mass murder cases involving a minimum of four victims from 1974 to 1979. Hickey (1997) identified serial murder cases from 1800 to 1995 through a variety of sources including newspapers, journals, biographies, interviews, bibliographies, and computer abstract searches. Anytime the media are used as a source of information, it becomes important to ascertain the existence of possible reporting biases. Kiger (1990) warns that “newspaper stories are problematic sources of data because they are obviously dependent upon editorial decisions and because they may sensationalize (not to mention glorify) this phenomenon in order to increase circulation” (p. 37). The media may be inclined to focus on particularly heinous cases or those involving a large number of victims, and ignore African-American (Jenkins, 1993a) and foreign offenders. In his analysis of the Henry Lee Lucas serial murder case, Egger (1990) found newspaper accounts were often inaccurate in their descriptions of details and had to be treated as suspect.

Kiger (1990) further cautions that a string of murders must first be identified as part of the same series before the existence of a serial killer will even be suspected (see the earlier discussion on linkage blindness). Newspaper reporting inaccuracies and definitional problems further complicate media source research. For example, upon perusing case details in microfilmed newspaper articles, Simonetti (1984) found some so-called incidents of serial murder were actually mass murders. Jenkins (1989) discusses the problems of historical changes in media practice and coverage, and the tendency towards greater coverage of events that occur in large urban areas. He notes major metropolitan papers expanded their coverage of regional issues in the 1950s, and since 1960 the proportion of national newspaper chains has tripled (1992b). In subsequent research, however, he concludes that such concerns do not present major research difficulties or significant data biases (1989).

These problems suggest a potential research bias. Crimes of repetitive killers who hunt over wide geographic regions may, because of linkage blindness, be unidentified as serial murders. Those attacks lacking a consistent M.O. and spread out over long periods of time are even less likely to be connected. Some serial murders may be officially known only as a number of unrelated missing persons reports. Such crimes fall into the “dark figure” of serial murder and are not open to traditional methods of information gathering, possibly skewing data collection towards more geographically confined serial murderers. But this begs the question; if a murder series is not identified in the first instance, then there is no need to assist in its investigation. It is also possible that purported but unidentified serial murderers, such as Jack the Ripper or the Green River Killer, never actually existed. While that conclusion is unlikely in these particular cases, it is certainly feasible the press or police might incorrectly link a number of

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unconnected homicides (see Jenkins, 1989). This is apparently what happened with a 1984 to 1985 series of murders of women in Fort Worth, Texas (Jenkins, 1993b).

9.2.1.3Offender, Victim, and Location Data

The second database (henceforth referred to as the SFU serial murder data set) contains microlevel information on offenders, victims, and locations for selected serial murder cases. It is based on a sample drawn from the FBI serial killer list, which served as a reasonable approximation of the overall population. While an accurate accounting of all serial murderers does not exist and most likely never will, the best efforts to date suggest the size of the modified FBI list is on the right order of magnitude (see Cavanagh, 1993; Hickey, 1997).

Specific criteria were employed to structure the sampling procedure. Only serial killers responsible for five or more victims, after 1960, who were residentially stable, operated by themselves or with a single partner, and who hunted in certain ways, were included (see Rossmo, 1995a, for complete details of the sampling methodology). The selection process helped to define the appropriate limits of the analysis and prevent misapplication. To have value in the investigation of an unsolved serial murder case, such a classification must be determinable from information likely to be known to police prior to the killer’s apprehension. Research parameters were developed with this consideration in mind.

A sample of 10 cases was randomly drawn from those that met the selection criteria and used to examine the microlevel geography of serial murder. An additional three cases that violated various selection criteria were also studied in order to assess the impact of these violations. The resulting 13 cases served as the initial test group for the criminal geographic targeting algorithm used in geographic profiling.

Information in the SFU serial murder data set includes: (1) date of murder; (2) day of murder; (3) time of murder; (4) sequential case number;

(5) weapon; (6) vehicle use; (7) degree of offender organization; (8) serial killer classification; (9) hunting typology; (10) victim traits (specific or nonspecific); (11) victim selection (random/nonpatterned or nonrandom/patterned); (12) victim activity; (13) offender residence (address, and spatial coordinates); (14) offender workplace (address, and spatial coordinates); and, for all known crime locations connected to each murder, (15) area description; (16) neighbourhood type; and (17) spatial coordinates. Appendix B contains the serial murderer, victim, and crime location data coding forms. Data coding procedures and guidelines can be found in Rossmo (1995a).

Through the use of a relational database management system, crime locations were hierarchically connected through the common murder, and

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