R. v. Grant, 2015 SCC 9:
Defence‑led evidence is admissible where (1) the evidence is relevant to a fact in issue, and (2) the probative value of the evidence is not substantially outweighed by its prejudicial effects. The trial judge must therefore first determine whether the evidence is logically relevant to an available defence. Where the defence's theory is that an unknown third party committed the indicted crime, this factual foundation will be established by a sufficient connection between the crime for which the accused is charged and the allegedly similar incident(s) suggesting that the crimes were committed by the same person, coupled with evidence that the accused could not have committed the other offence. Once a sufficient connection is shown, the evidence will be admissible unless its prejudicial effects substantially outweigh its probative value. This assessment is inherently individualized, and is capable of responding to various levels and forms of prejudice. It does not require the accused to satisfy a higher admissibility threshold or require the trial judge to engage in an enhanced evaluation of the evidence. The trial judge may not invade the province of the jury and determine the strength of the evidence.