In the Canadian criminal justice system, an accused has a right to challenge the evidence of a witness for the prosecution through the process of cross-examination.
The right of an accused to conduct a thorough cross-examination of a Crown witness is fundamental to a fair trial. As stated by Justices Major and Fish, speaking for a unanimous Supreme Court of Canada in R. v. Lyttle, 2004 SCC 5:
Cross-examination …remains a faithful friend in the pursuit of justice and an indispensable ally in the search for truth. At times, there will be no other way to expose falsehood, to rectify error, to correct distortion or to elicit vital information that would otherwise remain forever concealed.
That is why the right of an accused to cross-examine witnesses for the prosecution -- without significant and unwarranted constraint -- is an essential component of the right to make full answer and defence. [Beginning at paragraph 1, emphasis in original]
A trial judge risks undermining the fairness of a trial by improperly constraining or interfering with Defence counsel’s cross-examination of a witness for the prosecution.
Lyttle also sheds light on the governing principles of cross-examination. The Court confirmed that:
· Defence counsel is permitted to make an assertion to a witness for the prosecution as long as there is a “good faith basis” for doing so (para. 47);
· A "....'good faith basis’ is a function of the information available to the cross-examiner, his or her belief in its likely accuracy, and the purpose for which it is used. Information falling short of admissible evidence may be put to the witness. In fact, the information may be incomplete or uncertain….The cross-examiner may pursue any hypothesis that is honestly advanced on the strength of reasonable inference, experience or intuition...” (para. 48);
· The Defence is not required to independently prove the basis for an assertion made to a witness for the prosecution. "It is not uncommon for counsel to believe what is in fact true, without being able to prove it otherwise than by cross-examination; nor is it uncommon for reticent witnesses to concede suggested facts - in the mistaken belief that they are already known to the cross-examiner and will therefore, in any event, emerge..." (para. 47, emphasis in original);
· If a trial judge has a concern that defence counsel is making groundless assertions “…a trial judge may properly take appropriate steps, by conducting a voir dire or otherwise, to seek and obtain counsel’s assurance that a good faith basis exists for putting the question…” (para. 52);
· Defence counsel is not permitted to make an assertion to a witness that counsel knows to be false (para. 48); and
· Defence counsel is prohibited from engaging in “harassment”, “misrepresentation” or “repetitiveness” (para. 44).