In an attempt to overcome the obstacles facing serial violent crime cases, a variety of law enforcement strategies have been developed over the past few years (Egger, 1990). One of the cornerstones of this effort has been the creation and use of behavioural science-based methods in the police investigative process. The application of scientific studies of human behaviour to analyze criminal actions has led to linkage analysis systems, criminal profiling, geographic profiling, and crime-specific statistical databases. This field is sometimes referred to as forensic behavioural science to distinguish it from the more academic pursuits of traditional psychology and sociology (though one could argue that “forensic,” which means “belonging to courts of law,” is not the most appropriate term for a set of methods primarily investigative in nature).

Connected to the behavioural science approach has been the design of information management systems and suspect prioritization methods to enhance investigative effectiveness and efficiency (Jackson, van den Eshof, & de Kleuver, 1994; Ressler & Shachtman, 1992). Scrutiny of people of interest, in the effort to work backwards from them to the victim, is a difficult and time consuming process. Thorough interrogations of suspects, detailed interviews of their associates (who may be witnesses, whether they know it or not), and extensive searches for, and analyses of, physical evidence consume valuable and limited resources. By using a methodology to prioritize the police approach, investigative efforts can be tailored to the priority rating of the individual suspect. By focusing on the most probable suspects, all else being equal, the offender will more likely be identified sooner.

Kind (1987b, 1990) suggests the use of “frames” and “forms” to help prioritize suspects during the course of a police investigation. Frames are flexible and fuzzy enclosures employed to delineate potential suspects, while forms are tendencies for groups of people to behave in like fashion. Utilized in conjunction with each other, these concepts produce combined (i.e., intersecting) frames that outline the most productive lines of inquiry. While all criminal investigations can employ this form of information management, the approach is particularly useful in large-scale major inquiries.

4.2.1Linkage Analysis

When FBI Special Agent Clarice Starling finds a Black Witch Moth (Erebus odora) chrysalis lodged in the throat of serial killer Buffalo Bill’s latest victim, a connection is soon made to another murder. But real crimes, unlike those in Thomas Harris’ popular novel Silence of the Lambs (1988), are often much more difficult to link. “Prostitute strangled, dumped at the side of the road, no physical evidence,” is a depressingly familiar crime scene description.

Establishing which offences are part of a series is an important and essential task in the investigation of serial crime (see Gottlieb, Arenberg, & Singh, 1998). This process is known as linkage analysis20 or comparative case

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analysis (CCA). Realizing the extent of the crime pattern helps determine the appropriate level of police response, facilitates information sharing between investigators and jurisdictions, outlines case similarities, and identifies common suspects. If and when the case is solved, additional crimes are cleared and the court delivers a more appropriate sentence (including dangerous offender or habitual felon designations). Knowing all the pieces of the puzzle allows a more comprehensive picture of the offender to be formed and prevents linkage blindness from occurring.

For example, during 1993 and 1994 the Tag Team Rapists broke into several ground floor suites in Surrey, British Columbia, and attacked single women, many of whom had children. The crimes were occurring close together, but within two separate neighbourhoods (Newton and Bear Creek) that were a significant distance apart. One of the questions concerning investigators was the offender’s method of travel — on foot or by vehicle? Project Escalate’s first step was to examine all possible related crimes, including sexual assaults, attempts, burglaries, and prowlings. Eventually 14 different incidents were identified as being part of the series. Weather conditions on the dates and times of these events were then checked with the Environment Canada Vancouver Weather Information office. It was determined that every one of these incidents occurred on a dry night. The probability of this many fall and winter nights in the rainy Pacific Northwest without precipitation is very low. This suggested that the offenders intentionally refrained from hunting during inclement weather, an indicator they usually walked. The two offenders have now been apprehended and convicted, and this prediction turned out to be accurate. But the question of offender transportation could not be answered with any degree of confidence until after the linkage analysis had been completed and as many of the pieces of the puzzle as possible assembled.

There are three main methods used by police investigators to link crimes prior to an offender’s apprehension. They are: (1) physical evidence;

(2) offender description; and (3) crime scene behaviour. Each method has its strengths and weaknesses. It is not uncommon for a series of crimes to be connected through a combination of these means.

4.2.1.1Physical Evidence

Physical evidence provides the most certain means of linking crimes, though evidence of a type suitable for doing so may not be present in every case. One of the more powerful forensic methods, DNA profiling, has been heralded as the most revolutionary technology in the field of criminal

20 This is not to be confused with the similar but distinct function of “link analysis,” performed on such systems as the i2 Analyst’s Notebook. Link analysis examines interand intra-crime associations between names, telephone numbers, vehicles and the like. Linkage analysis considers likelihood of crime similarity.

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investigation since the development of the Henry System for fingerprinting (Bigbee, Tanton, & Ferrara, 1989; Burke & Rowe, 1989; Eisner, 1989; Gaudette, 1990; Kelly, Rankin, & Wink, 1987; Lowrie & Wells, 1991; Wambaugh, 1989). As both semen and blood contain DNA, the potential for ascertaining and verifying links in cases of violent and sexual crimes is significant. One of the necessary steps to realize the potential of DNA analysis is the establishment of centralized indices to facilitate computerized searches and comparisons (Adams, 1989; Miller, 1991).

In 1990, the FBI began development of a national DNA identification index, completing the combined federal, state, and local police agency pilot project in 1993 (Brown, 1994; see also Weedn & Hicks, 1998). Designed for the compatible storage and comparison of DNA records, the Combined DNA Index System (CODIS) consists of two investigative indices — the forensic index for unsolved crimes, and the convicted offender index for known felons. A missing persons and unidentified bodies index will also be part of the system.

One of the important functions of such a system is the establishment of series crimes (Brown, 1994). For example, DNA pattern matching linked 18 unknown suspect serial cases together in Minnesota, eventually helping to solve them by matching specimens of two offenders to the crime scenes. Such results are more common in Britain where a DNA database has been in existence for some time (Davies & Dale, 1995b; “DNA profiling,” 1995). As of May 1997, it has been responsible for over 5000 hits — defined as a match between crime scenes or between crime scene and offender — in the U.K. Canada has also enacted legislation for the establishment of a national DNA data bank.

Automated fingerprint identification systems (AFIS) — the method that identified Richard Ramirez as the Night Stalker — are becoming increasingly common in police agencies, allowing comparisons and matches that sheer volume would have previously precluded (Sparrow, 1994). Programs such as the Integrated Ballistics Identification System (IBIS), networked into the joint ATF/FBI National Integrated Ballistic Information Network (NIBIN), link crimes committed with firearms through computerized comparisons of microscopic bullet striation patterns and shell casing marks (Dees, 1994; Strandberg, 1994; see also Davis, 1958; Di Maio, 1985). And the British Shoeprint Image Capture and Retrieval System (SICAR) is a national database that connects crime scenes through the geometrical shapes associated with stored images of footprint evidence.

4.2.1.2Offender Description

Descriptions of offenders have provided a common and long used method of linking crimes. Mug shot books, while still in existence, are being replaced by computerized photographic databases that allow for certain physical description parameters to be used to narrow the search.

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This is all predicated upon the assumption that there was a witness to the crime. There may not be one in the case of murder or arson. Even in a sexual assault, the victim must see, remember, and accurately recall (acquire, retain, and retrieve) the offender’s description. The ability for investigators to obtain an accurate physical description depends upon such factors as lighting conditions; whether the offender was masked; if the attack was from the rear; and the level of victim trauma, stress, fright, alcohol use, forgetfulness, and cooperation.

Individual physical appearance is also subject to modification. Weight changes slowly, hair more quickly, and clothing daily. Even more stable descriptors such as age, race, height, and build will be viewed subjectively by different victims. Ted Bundy, for example, was able to tremendously vary his description as can be seen from photographs and police “wanted” posters (Michaud & Aynesworth, 1983; Winn & Merrill, 1979).

The prevalence of video cameras has enhanced the ability of police to use offender descriptions. Most banks and financial institutions, and many businesses, transportation centres, and building lobby areas have been outfitted with video cameras. CCTV (closed circuit television) coverage of city centres, parking lots, and other public places is now common in Britain. Police agencies make routine use of the photographs and videotape from these cameras to assist in their investigations.

Automated recognition systems for digital facial images now exist and are used for both comparison and identification purposes (Mardia, Coombes, Kirkbride, Linney, & Bowie, 1996). Distance and angle measurements are taken between certain facial points (e.g., from lower point of the ear to nose tip, the tangent to chin tip and nose tip, etc.) for both anterior (front) and profile (side) views. Horizontal and vertical landmarks are calculated to produce a mathematical “profile” of the face. This landmark-based data then provides the means of determining correlations between facial images.

These systems can be connected to video cameras placed within airport terminals and used to scan custom and immigration lines. A match with an image in the facial database alerts officials to the possible presence of a person of interest, such as a criminal, missing person, fugitive, abducted child, or terrorist. Police investigators have also used computerized facial recognition systems to assess the probability that two robbers captured on bank cameras are, in fact, the same person. These methods increase the value of offender image data, and echo the early work of Alphonse Bertillon in criminal identification through body measurement.21

21 Ear patterns are also unique and have been used successfully to identify both criminals and victims.

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