Blurred Lines: A Critical Examination of the Use of Police Officers and Police Employees as Expert Witnesses in Criminal Trials

Abstract

There is a two-step inquiry in determining whether expert opinion evidence is admissible. The party calling the evidence must first satisfy the threshold requirements of admissibility, demonstrating that the expert evidence is relevant, necessary, not precluded by any exclusionary rule, and that it is provided by a properly qualified expert. If this threshold stage is satisfied, the court progresses to the second stage, the discretionary gatekeeping step, wherein the trial judge assesses whether the expert evidence is sufficiently beneficial to justify admission, meaning that the benefits flowing from admission outweigh any potential harm. The Supreme Court of Canada has clarified that experts must be impartial, independent, and unbiased. These factors must be considered at both steps of determining the admissibility of expert evidence and are also relevant to the determination by the trier of fact as to how much weight should be placed upon admissible expert testimony. That there are three potential points in the trial process at which expert objectivity is considered underscores the importance of ensuring that expert evidence is impartial, independent, and free of bias. This paper analyzes recent Canadian case law in relation to the use of expert witnesses and determines that structure-related concerns ultimately pertaining to bias have played a significant role in court determinations as to the admissibility of expert evidence. Guided by this finding, the authors propose a new two-stream expert structure in order to present a model for proactively reducing concerns relating to impartiality, independence, and bias about experts called by the Crown