Two cases from the Supreme Court of Canada concern the directions a judge should give to a jury on the need for caution about the evidence of an "unsavoury" witness: R v Khela  SCC 4, applied in R v Smith  SCC 5, both 22 January 2009.
Unsavoury witnesses "...include all witnesses who, because of their amoral character, criminal lifestyle, past dishonesty or interest in the outcome of the trial, cannot be trusted to tell the truth — even when they have expressly undertaken by oath or affirmation to do so." (3, Fish J delivering the judgment of himself and Binnie, LeBel, Abella, Charron and Rothstein JJ; Deschamps J separately concurred).
The required elements are rational and will no doubt be of interest outside Canada.
There is no precise formula, but the direction must (I summarise):
- Identify the evidence about which the jury needs to be cautious;
- Explain why caution is necessary;
- Caution the jury on the danger of convicting in reliance on the testimony of the unsavoury witness, although the jury is entitled to do so if satisfied that the evidence is true; and
- Instruct the jury to look for independent evidence which gives comfort that the unsavoury witness is correct (drawing attention to what evidence is capable of confirming the unsavoury witness in the relevant way).
A subsidiary appeal point in Khela concerned a direction that wrongly told the jury that the defence needed to prove certain facts in order to support an inference of innocence (58). However, the Court of Appeal had correctly applied the proviso on the basis that in context the misdirection would not have made any difference to the verdicts.
The unsavoury witness directions set out here would be a good framework on which counsel might structure that part of the address to the jury. It is always a good idea to try to persuade the jury in terms that will be repeated by the judge.