Canadian Criminal Evidence/Credibility/Collateral Fact Rule

General Principles
A collateral is a "fact not directly connected" or not relevant to "the issue in dispute" Collateral facts are not generally admissible. Any extrinsic contradictory evidence that brings a witness' credibility into question may not be considered where the contradictory evidence not relevant to an issue at trial. When a witness speaks to a fact, the veracity of the testimony can only be brought into question where it is sufficiently material to a trial issue. Otherwise, it will fall up against the collateral fact rule that prohibits the calling of contradictory evidence on immaterial facts. Thus, testimony on collateral issues is conclusive. This rule has been codified in certain legislation including s. 10 and 11 of the CEA.

A foundational test for collateral fact is whether the evidence contradicting the statement of the witness could be validly led as evidence on its own. Thus, statements to evidence that is not directly connected to a material fact cannot be contradicted.

The rule equally applies in cases that turn on credibility.

Exceptions exists for certain evidence going to credibility:
 * existence of material previous statement
 * prior convictions
 * honesty or history of lying
 * bias or partiality
 * motive to fabricate
 * bad reputation
 * perception
 * memory
 * ability to communicate.

Where a witness denies having an animus against the accused at the time of the offence may be contradicted with extrinsic evidence. However, where a witness concedes having an animus against the accused at the time of the offence, they may be cross-examined on an ongoing animus including at the time of trial.