From time-to-time, police officers will testify as experts on the basis of expertise that has been obtained through practical experience on the job over many years.
The boundaries of any proposed expert opinion must be carefully delineated. As well, the trial judge must ensure that the expert stays within the bounds of their expertise and that the evidence is properly the subject of expert evidence. The guilt or innocence of accused persons that the police officer had encountered in the past is generally not legally relevant to the accused’s guilt or innocence. [FN1]
In R. v. J.T., 2021 ONCA 922 (CanLII), the Appellant argued that unlawful pornography had been automatically downloaded onto his computer. The forensics police officer gave evidence that in his experience he had never seen child pornography end up on a computer in an automatic fashion. The judge relied on this evidence and ultimately convicted the accused. The admission and reliance of the evidence was challenged on appeal on the basis that it was unnecessary and irrelevant anecdotal testimony and–essentially–that in relying upon this evidence, the court was imputing the guilt of the accused from the guilt of other similarly situated offenders.
The ONCA disagreed holding that the evidence was experience-based and had been provided to explain the technical operation of computers, specifically, that documents are not automatically downloaded by computers, but by human action.
[FN1] See R. v. Sekhon, 2014 SCC 15.