Admissibility of expert evidence – scientific versus police experts

(This is an excerpt of a paper authored by Joven Narwal for the 2014 Canadian Bar Association National Criminal Justice Conference held April 12, 2014)

The Mohan test for the admissibility of expert evidence is not readily applied to the anecdotally-based expertise of police witnesses. The problem, as Professor Moreno described it in, “What Happens When Dirty Harry Becomes An (Expert) Witness for the Prosecution?”1, is that unlike scientific and technical expertise gained through education, training and empirical research, a law enforcement opinion derived from personal experiences is a “self-validating discipline”, without identifiable methods, standards or objective criteria. The practical result is that these experts are often immunized from effective cross-examination on the foundation of their opinions. A real danger arguably exists that the intuition and mere suspicion of these officers, voiced under the guise of expertise, may stray from its limited use and usurp the role of the trier of fact or otherwise cause an inordinate prejudicial effect. For instance, although expert testimony from police officers has been held to satisfy the necessity criterion because the rules, norms, standards and customs of the drug trade are outside the experience of the average person, this type of evidence can venture dangerously close to a form of criminal profiling, the probative value of which has been criticized2; the evidence may also tend to suggest that the accused had criminal associations, thereby introducing evidence of bad character3. Despite these dangers, the reality remains that the Crown is often not able to lead direct evidence of the accused’s intentions therefore requiring inferences to be drawn through expert evidence, and as the Court of Appeal for the First Circuit noted in United States v. Hoffmann, this type of “expertise is not necessarily synonymous with a string of academic degrees or multiple memberships in learned societies [as] hard-core drug trafficking scarcely lends itself to ivied halls”.

The Supreme Court of Canada recently addressed the admissibility of anecdotally based expert evidence from a police witness in R. v. Sekhon 2014 SCC 15 [Sekhon]. The accused was convicted of importation and possession of 50 kg of cocaine for the purposes of trafficking in a false compartment secreted in the bedliner of a truck which he drove across the border into Canada. The main issue at trial was whether the accused had knowledge of the cocaine. The accused testified that he did not know cocaine was in the truck. The Crown called a police expert to provide information about the trade and customs surrounding the importation of cocaine into Canada. The expert testified that he had never encountered a “blind courier” in a thousand investigations and thus in his experience, the person involved in transport would be aware of the illicit load. The trial judge relied on this evidence in convicting the accused. On appeal, Newbury J.A. in dissent found that the evidence was “purely anecdotal evidence, not amenable to cross-examination in any real sense, from an officer who was not in a position to determine as a matter of fact whether in all of the approximately 1,000 cases he had investigated, the courier had been ‘blind’ or not”. She held that the evidence “provided no assistance to the Court as to whether the accused had known what he was transporting”, but rather tended to “short-circuit” the inquiry. On further appeal, Moldaver J., for the majority, agreed with Madam Justice Newbury as to the prejudicial effect of the evidence, and held that the trial judge erred in relying on the evidence. Although the conviction was ultimately upheld by application of the curative proviso, this was the first time the Supreme Court of Canada ruled on the admissibility and use of anecdotally based custom of the trade evidence and in doing so, reaffirmed the fundamental principles surrounding admissibility of expert evidence. Unfortunately, the judgment does not address the fact that the impugned evidence was inconsistent with five recent cases in British Columbia in which police experts had testified as to existence and possibility of blind couriers being used.5 The inherent unreliability of the evidence was addressed in principle but the ruling does not provide any direction or guidance that could assist in creating standards or codes of conduct for police expert witnesses that could address the reliability concerns.

This paper explores the admissibility of anecdotally-based expertise of police witnesses, against the backdrop of these issues. We begin with an overview of the general principles regarding the admissibility of expert evidence. In the context of that review, we highlight that threshold reliability of the opinion evidence has become recognized as a primary concern, although not specifically enumerated in the Mohan test. We then turn to a review of the modified Mohan test, developed by Doherty J.A. in R v. Abbey, 2009 ONCA 624 [Abbey], which has become a leading authority on the admissibility of expertise gained through years of practice, study, experience and training. We conclude with a review of the Supreme Court of Canada’s recent decision in Sekhon, which highlights that admissibility is not an all or nothing proposition: defence counsel facing the dangers of anecdotally-based police expert evidence can still seek to limit the opinion using the well-worn fundamental principles of admissibility.