[1]          The law regarding expert witnesses has evolved considerably over the last 20 years. Gone are the days when an expert served as a hired gun or advocate for the party that retained her. Today, expert witnesses are required to be independent, and their function is to provide the trier of fact with expert opinion evidence that is fair, objective and non-partisan.

[2]          The role of the trial judge in relation to expert witnesses has also evolved. Appellate courts have repeatedly instructed trial judges that they serve as gatekeepers when it comes to the admissibility of expert opinion evidence. They are required to carefully scrutinize, among other things, an expert witness’s training and professional experience, along with the necessity of their testimony in assisting the trier of fact, before the expert is qualified to give evidence in our courts. This gatekeeper role is especially important in cases, such as this one, where there is a jury who may inappropriately defer to the expert’s opinion rather than evaluate the expert evidence on their own.

[3]          In the present case, the trial judge qualified an expert to testify on behalf of the defence despite some very serious reservations about the expert’s methodology and independence. It became apparent to the trial judge during the expert’s testimony that he crossed the line from an objective witness to an advocate for the defence. Despite his concerns, the trial judge did nothing to exclude the opinion evidence or alert the jury about the problems with the expert’s testimony.

[4]          On appeal, the appellants advance several arguments to the effect that trial fairness was breached, such that a new trial is necessitated. All of these arguments focus on the impugned expert.

[5]          In my view, the appeal must be allowed and a new trial ordered. I reach this conclusion because the trial judge failed to properly discharge his gatekeeper duty at the qualification stage. Had he done so, he would have concluded that the risks of permitting the expert to testify far outweighed any potential benefit from the proposed testimony.

[6]          In addition, the trial judge’s concerns about the expert’s testimony were substantially correct; the witness crossed the boundary of acceptable conduct and descended into the fray as a partisan advocate. In these circumstances, the trial judge was required to fulfill his ongoing gatekeeper function and exclude in whole or in part the expert’s unacceptable testimony. Instead, the trial judge did nothing, resulting in trial fairness being irreparably compromised.