The Quebec Court of Appeal ordered a new trial of a man convicted of killing three people because the trial judge provided inadequate instructions to the jury over the weight that should be given to post-offence conduct and because he failed to warn the jury that the testimony of the prosecution’s expert went beyond the bounds of his expertise.

The ruling, the second time in six years that the Quebec appeal court set aside a murder conviction and ordered a new trial because of testimony provided by psychiatrist Sylvain Faucher, highlights pervasive concerns about expert bias and examines the credence that should be given to post-offence conduct, according to criminal lawyers.