Police Officers are not DNA experts

The latest Canlii Connects case summary takes a look at R. v. Sutherland, 2022 MBCA 23 and touches on issues of the scope of expert evidence and and what an appeal court can do if they find there was an error at trial but determine it didn't impact the outcome.

Issue: Did the trial judge err in admitting a police officer's opinion evidence about DNA?

Facts: Mr. Sutherland convicted by a jury of second degree murder. His former co-accused had plead guilty and testified that he and Mr. Sutherland had stabbed the victim to death in the course of a robbery. There was no DNA evidence of either Mr. Sutherland or Mr. Conway at the crime scene. There was also no blood or DNA found on Mr. Sutherland’s clothing connecting him to the scene or the deceased despite there being a large amount of blood at the scene. 

Despite the investigating officer having no training in regard to DNA he was permitted to opine on his belief as to why there was an absence of DNA located.

Specifically he testified to sources of DNA, how DNA ends up at crime scenes, whether DNA is subject to contamination, environmental factors that can remove or disintegrate DNA, whether DNA is found at all crime scenes, and whether a perpetrator’s DNA would necessarily be found at a crime scene and, specifically, at this scene. 

Ruling:  The Court found that the trial judge had erred in allowing the opinion evidence but applied the curative proviso to dismiss the appeal. 

This issue turned on the distinction between expert opinion and lay opinion evidence. 

The fundamental question to ask in determining whether the evidence requires a qualified expert is whether the opinion could be formed only by someone with special training or expertise, which is expert opinion evidence, or whether the opinion is based on ordinary experience, making it lay opinion.

DNA evidence was such that only a qualified expert could opine on it. It falls beyond the scope of what has been recognized as lay opinion. The specific officer did not have the experience or training required to offer expert opinion. As a result the evidence ought not to have been admitted. 

In the result, however, the court found that the error was harmless. They reasoned:

In my view, the absence of DNA of the accused or Conway at the scene was not significant, indeed was of no import, to the jury’s determination of the accused’s guilt because there was no DNA found there other than that of the victim, despite the fact that the victim had clearly been killed by someone.  Therefore, as a matter of logic and common sense, the absence of DNA of the accused or Conway at the scene could not have impacted the jury’s determination regarding the accused’s culpability.  Accordingly, Sgt. Catellier’s inadmissible evidence, led for the purpose of explaining away that absence of DNA, was superfluous and, as such, inconsequential. 

 Given that conclusion there was no reasonable possibility of a different verdict had the error not occurred. The high burden to apply the curative proviso had been met.