As part two of my earlier blog on the issue of expert witnesses at trial, Bruff-Murphy v. Gunawardena, 2017 ONCA 502, is a great read for the Court of Appeal’s view on the role of the trial judge during expert testimony.
In the introduction alone, Justice Hourigan was clear that “gone are the days when an expert served as a hired gun or advocate” (para. 1) and that it is the trial judge’s role to act as a gatekeeper so that the expert opinion evidence before the court is “fair, objective and non-partisan” (para. 2).
While my earlier blog focused on the legal test during the qualification stage, Justice Hourigan was also clear that the trial judge does not become functus the moment an expert witness is permitted to give expert opinion evidence. Rather,
“The trial judge must continue to exercise her gatekeeper function. After all, the concerns about the impact of a non-independent expert witness on the jury have not been eliminated. To the contrary, they have come to fruition. At that stage, when the trial judge recognizes the acute risk to trial fairness, she must take action” (para. 63).”
In this case, Justice Hourigan commented that there were various options available to the trial judge after the qualification stage, which trial counsel should also be aware of as suggestions in their toolkit. To quote Justice Hourigan at paragraphs 67 and 68 of this decision,
 Given this ongoing gatekeeper discretion, the question remains of what, as a practical matter, the trial judge could or should have done in this case. His first option would have been to advise counsel that he was going to give either a mid-trial or final instruction that Dr. Bail’s testimony would be excluded in whole or in part from the evidence. Had he taken that route, he would have received submissions from counsel in the absence of the jury and proceeded as he saw fit. Alternately, he could have asked for submissions from counsel on a mistrial, again in the absence of the jury, and ruled accordingly. In the event that he had to interrupt Dr. Bail’s testimony mid-trial, he would have had to consider carefully how best to minimize the potential prejudicial effect of the interruption from the respondent’s perspective.
 The point is that the trial judge was not powerless and should have taken action. The dangers of admitting expert evidence suggest a need for a trial judge to exercise prudence in excluding the testimony of an expert who lacks impartiality before those dangers manifest.
Thanks for reading this week!