tigation suffers from an incomplete pattern and the profile is missing important data. Proper information collection — from the crime scene, during the follow-up investigation, and as part of routine police practice — is particularly important (Bekerian & Jackson, 1997); also, the value of a profile is significantly enhanced when it is combined with other investigative tools, both behavioural and traditional.

Profiling is not independent of other forms of investigative analysis. A framework for crime analysis methods has been developed by Mario de Cocq (1997), head of Interpol’s Analytical Criminal Intelligence Unit (ACIU). Analytic techniques are first classified as either strategic or operational, and then grouped by focus on criminal incident, offender, or crime control method. Within this framework, “specific profile analysis [unknown offender(s)]” — psychological and geographic profiling — is categorized as operational/offender. Comparative case (linkage) analysis is categorized as operational/criminal incident. This approach allows for both similarities and differences between analytic methods to be readily identified.

Part of the difficulty with profiling has been its probabilistic nature. Police investigators are uncomfortable with such methods of inquiry, preferring instead to rely upon “certainties.” This often leads to problems in the understanding, use, and evaluation of profiling services. The following example clarifies the point. A man consults a statistician before gambling on a game of dice. He is advised that the number most likely to turn up is 7, and he bets accordingly. But when he rolls a 5, the bet is lost.

Was the advice inaccurate? Well, any student of probability knows that 7 is the most likely number to result from the roll of a pair of dice, with 2 and 12 being the least likely. Still, the probability of 7 occurring in any single roll is only 1 in 6. The statistician’s advice was not a prediction — in fact, a better forecast (with a 5/6 chance of being correct) would have been a number other than 7. Rather, the advice was a statement regarding the most likely single outcome. While the prediction was wrong, it was also accurate, and any future prediction would still be 7. This information is thus of greater value when used over the course of a series of games. In other words, while no one can predict a given spin of the roulette wheel, there is little doubt the house will make money at the end of the day. Similarly, profiling is optimally employed by an investigation when it assists in the direction of repetitive efforts and the prioritization of volume work.

5.7 Expert Testimony

Expert testimony from profilers has been introduced now in both American and Canadian courts. Subject matter has included future dangerousness,

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threat level, similar fact evidence, case linkage, crime scene signature, staging, and insanity (see Keppel, 1989, 1995; Keppel & Birnes, 1997). Profiling has also played a role in premises liability litigation where the court must establish if the proximate cause of damages was a breach of duty to provide proper security (Kennedy & Homant, 1997). Opinion evidence regarding likely criminal response to security measures influences establishment of a cause-in- fact relationship between the alleged negligence and plaintiff injury. In these circumstances, most of the profile is an attempt to predict the behaviour of the typical offender — persistence, desistance, or displacement — under certain security conditions. While such information may assist juries in appropriate cases, prediction of specific individual behaviours with any degree of confidence is difficult, even for experts (Homant, forthcoming).

This is particularly so when the offender is unknown (i.e., not identified and apprehended). Homant (forthcoming) proposes a typology for offender deterrence based on factors of criminal motivation and desire to avoid capture: (1) calculating — motivated and cautious; (2) opportunistic — unmotivated and cautious; (3) determined — motivated and incautious; and (4) impulsive — unmotivated and incautious. Adjustments are made based on offender intelligence, target significance, and evidence of irrationality (e.g., use of drugs or alcohol). Profiling can play a role in premises security litigation through interpreting signature, reconstructing crime scenes, and assessing motivation.

To be so designated, an expert witness must meet three requirements:

(1) their testimony must be relevant; (2) their field must require scientific, technical, or specialized knowledge; and (3) they must have the necessary background to qualify as an expert in the field (e.g., skill, specialized training, formal education, experience) (Garland & Stuckey, 2000). Relevance has been defined as evidence that affects the probability of existence for facts of consequence to the trial (Robertson & Vignaux, 1995). Until 1993, determination of “scientific knowledge” used to follow the Frye test (Frye v. United States), which asked if the knowledge was generally accepted as reliable within the relevant scientific community. That year the U.S. Supreme Court decided that U.S. Federal Rules of Evidence superseded Frye (Daubert v. Merrell, 1993). The Daubert test is now used to determine if a subject matter has reached the stature of “scientific knowledge.” It is a more flexible and less stringent test than Frye, and is based on the following factors: (1) falsifiability (the testability of the technique); (2) peer review and publication; (3) the actual or potential error rate and the maintenance of operational standards; and (4) general acceptance of the methodology within the relevant scientific community. These are currently the principles guiding admissibility of scientific evidence in American courts.

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The Canadian test is not as strict as the U.S. one. In R. v. Mohan (1994), the Supreme Court of Canada outlined the requirements for admissibility of expert evidence: (1) relevance to a fact in issue; (2) necessity in assisting the trier of fact; (3) absence of an exclusionary rule; and (4) a properly qualified expert. Novel scientific theories or concepts are subject to special scrutiny concerning their validity and reliability. This scrutiny is a flexible test that considers acceptance within the scientific community; suggested criteria include testability, peer review, and publication. Canadian courts have stated that expert opinion evidence can be rendered to assist the trier’s understanding of psychology, behaviour, and human conduct; but they have also cautioned that the confirmation methods used in profiling “should be considerably sharpened and disciplined” (R. v. Clark, 1998, p. 21). Profiles are not generally introduced as evidence in British courts.

Profiling is based on inductive, probabilistic methods. What is the proper role of such evidence in the courtroom? All science is inductive and scientific “laws” are only predictions based upon repeated observations. By contrast, deductive systems are derived from axioms or established rules. The only true deductive system is mathematics, though many scientific theories are so well accepted they are often treated as established facts in normal life for all intents and purposes. It has been said that science is quantitative and law is qualitative (Forst, 1996a). For example, “beyond a reasonable doubt,” the standard for criminal conviction, is a subjective determination and has not been translated by either statute or case law into a specific number.28 Generally, probabilistic information is valid, especially in cases involving circumstantial evidence, though experts are ill advised to go beyond the established boundaries of their discipline. They must also be prepared to articulate the logic and specify the data upon which their conclusions are based (Homant, forthcoming).

The most appropriate manner of introducing and weighing profiling expertise in court is through the use of Bayesian probability methods. Bayes’ rule is a logical theorem that provides the means of updating probabilities given new information of relevance (Iversen, 1984). It can be expressed as follows:

The prior odds are those that existed before the new information, and the posterior odds, those after. Probability always ranges between 0 and 1; odds are the ratio of the probability that something is true to the probability that it is not: p / (1 – p). The likelihood ratio is the quotient of the probability

28 In a survey of 1200 U.S. judges, two-thirds thought “beyond a reasonable doubt” represented a probability of guilt of at least 95%.

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of the evidence given that an assertion is true (i.e., the accused individual is guilty), divided by the probability of the evidence given that the assertion is false (i.e., an accused individual is innocent). This can be expressed as follows:

The probability of guilt given the evidence (P(G|E)) can be determined from the probability of the evidence given guilt (P(E|G)). According to Bayes’ rule:

If the probabilities of guilt and innocence are equal (i.e., P(G) = P(I) = 0.5), then the above equation simplifies to: P(G|E) = P(E|G). The higher the prior probability of guilt, the more attenuated the impact of the evidence (likelihood ratio) on the posterior probability of guilt.

Expert testimony, however, should be limited to providing the likelihood ratio resulting from the observation, profile, or test result. Behaviour science evidence, whether it be similar fact, signature, psychological, or geographic in nature, can only be justified on this basis. Estimating probability of guilt or innocence assumes knowledge of the prior odds, and this determination is the responsibility of the judge or jury — not the expert witness (Robertson & Vignaux, 1995).

Errors in the use of probability within the court context unfortunately are not uncommon. The prosecutorís fallacy results from transposing the conditional in either the numerator or denominator of the likelihood ratio (see also Martin, 1992). This occurs, for example, when the probability of the evidence given guilt, P(E|G), is equated with the probability of guilt given the evidence, P(G|E). In other words, while all cows are four-legged animals, not all four-legged animals are cows. This type of error within a behavioural science context results if: (1) a crime scene indicates a certain personality profile with a 90% level of confidence, and the assumption is made that a person who matches the profile is 90% likely to be guilty (transposing the conditional in the numerator); or (2) only 10 murders out of a database of 50,000 exhibit a specific crime scene behaviour, and the conclusion is reached that the probability of such a similarity occurring by chance is one in 5,000 (transposing the conditional in the denominator, also referred to as the coincidence fallacy). The former type of error occurred in the aftermath of the 1996 Atlanta Olympics pipe bombing. Security guard Richard Jewell became a major suspect in the investigation simply because he fit the FBI profile for a certain type of bomber. Effectively branded guilty, it took several weeks before he was eventually cleared (Reid, 1996).

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The defence attorney’s fallacy occurs when evidence is considered in isolation, rather than as a totality. It is the combined impact of different, and independent, evidential elements that is important.29 This type of error within the behavioural science context results if a profile is ignored because it lacks dramatic discriminatory power, instead of the findings considered in conjunction with other existing evidence, and used to increase the posterior odds appropriately.

5.8 Future of Profiling

Notwithstanding his claim to be a consulting detective, Sherlock Holmes employed inductive methods almost as often as deductive ones (Teten, 1989). Despite his renowned successes, such procedures by their very nature carry a certain failure rate. Wrong predictions are part of any probabilistic-based methodology, including profiling (Homant & Kennedy, 1998). It is important that profiles be used by both providers and consumers in a careful and ethical manner, with an awareness of their limitations and an understanding of the proper application of stereotypes and prioritization methods. Grubin (1999) also cautions that profiling is not about “getting into the mind” of the criminal, and we should be concerned when the profiler becomes more newsworthy than the profile.

“In summary, there is enough research to suggest that crime scene profiling may have sufficient reliability and validity to be useful for some purposes. The literature suggests that the concept of behavioral traits and consistency across situations is respectable, if measured in broad contexts” (Homant & Kennedy, 1998, p. 338). The development of profiling and other forensic behavioural science techniques is in its early days. While this may sometimes result in frustration, it is also an exciting time with much potential for future evolvement. For example, offender profiling may benefit significantly from the application of fuzzy logic (Kosko & Isaka, 1993; Yager & Zadeh, 1994). Traditional Boolean logic is dichotomous and follows the law of the excluded middle — answers are either yes or no. Fuzzy logic allows for subjectivity and “maybes.” These shades of meaning can be given intermediate values between 0 and 1. Verma (1997) discusses how imprecise features and characteristics may be fuzzy variables. A sufficient number of such parameters can form a fuzzy prototype pattern class (e.g., young, tall, heavy, violent). This is similar to the concept of frames, flexible and fuzzy enclosures used to prioritize suspects during an investigation (Kind, 1987b, 1990). Estimating min-max values can help define the limits of the pattern

29 These errors in logic can also occur within a profile. Use of spurious, intervening, and non-independent variables is problematic and can distort an analysis.

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set. This approach can be of assistance in many ways, including the reconciliation of varying descriptions in a series of connected crimes. Austin (1996) used a fuzzy logic expert system for offender profiling that analyzed crime, victim, and event details to connect rapes to rapes, and offenders to rapes.

Profiling is a useful and promising investigative methodology. It is also a novel technique, the maturation of which requires a commitment to not only data collection, analysis, and research, but also to operational feedback and integration. Inductive systems require systematic methods for developing and expanding their knowledge base. It is thus critical for scientific and investigative methodologies to be concerned with issues of validity and reliability (see Oldfield, 1995). Profiling knowledge originates from experience, research, and statistical databases. While experience is important, if not vital, it can also be idiosyncratic, containing limitations and unrealized biases, upon which profiles may be based. Experience should therefore be triangulated with research findings. Specification of the limitations inherent in a method’s underlying assumptions is also important. Finally, a technique must possess utility if it is to have value in the real world of police investigation. Such considerations are what distinguish profiling predictions from psychic guesses.

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