A guilty plea by a co-accused, not called at trial, cannot be used to support the Crown’s case

R. v. C.G., 2016 ONCA 316:

[7]          This was an error. The trial judge also erred in using K.I.'s guilty plea to corroborate the evidence of the complainant. Had K.I. been available to be called as a witness – which he was not, as he died before the appellant's trial – his guilty plea would have been relevant to his credibility and to his own involvement in the sexual assault. However, a guilty plea by a co-accused, not called at trial, cannot be used to support the Crown's case. 

[8]          For example, in R. v. C. (P.), 2015 ONCA 30, 321 C.C.C. (3d) 49, a young offender was tried separately from four adults on a charge that he had aided and abetted a murder. The four adults pleaded guilty – one to murder, two to manslaughter, and one to aggravated assault. The trial judge instructed the jury that the guilty plea to murder by one of the four adults could be used as evidence against the accused. On appeal, this court held, at paras. 43-46, that the trial judge had erred:

The trial judge explained that the determination that Xiao had committed murder was the logical first step in deciding whether the appellant had aided and abetted Xiao in committing an unlawful act. She told the jury they could use that plea and conviction to conclude that Xiao had committed murder. 

The trial judge erred in law when she told the jury that it could use Xiao's guilty plea and conviction as evidence against the appellant. See R. v. Simpson, [1988] 1 S.C.R. 3; R. v. MacGregor (1981), 64 C.C.C. (2d) 353 (Ont. C.A.); R. v. Pentiluk (1974), 21 C.C.C. (2d) 87 (C.A.), at 92.

Xiao's guilty plea was no more than hearsay evidence that Xiao had committed murder, and could not be considered in determining the appellant's guilt. In R. v. MacGregor, Martin J.A. said, at pp. 357-58:

Admittedly, it was an error for the trial judge to fail to instruct the jury that in considering the case against the appellant they should disregard the pleas of guilty of manslaughter by the co-accused and that those pleas were not in any way to be taken into account in considering the case against the appellant.

This statement of the law was adopted by the Supreme Court in R. v. Simpson.

[9]          In the present case, it was an error for the trial judge to rely on K.I.'s guilty plea as support for the complainant's version of events.