Judges occasionally make harsh criticisms of the witnesses who appear before them. Sometimes those criticisms are justified; other times, everyone is just having a bad day. In these days of instant search, such a criticism could be recycled endlessly in subsequent cases, perhaps permanently damaging the credibility of the witness. This could end the courtroom career of a professional, such as an expert or police officer. But recycling old criticisms in this way is illegal, at least in Ontario and Alberta.
Many courts have ruled that a witness cannot be cross examined about what other judges have said about them. Previous judicial comments about a witness are irrelevant to unrelated testimony in another case.
The leading case is R. v. Ghorvei, where one judge had described a particular police officer as “a compulsive liar”. Defendants in subsequent cases investigated by that same police officer immediately argued that no subsequent judge (or jury) should believe the officer either. The Ontario Court of Appeal ruled that it was improper to cross examine the officer in subsequent cases about the “liar” comments by the previous judge:
 In my view, it is not proper to cross-examine a witness on the fact that his or her testimony has been rejected or disbelieved in a prior case. That fact, in and of itself, does not constitute discreditable conduct. I do not think it would be useful to allow cross-examination of a witness on what is, in essence, no more than an opinion on the credibility of unrelated testimony given by this witness in the context of another case.
- Per R. v. Deacon
Put simply, it would be a denial of justice for an accused person or the prosecution’s case to be judged on the basis of findings of fact and of credibility in another proceeding.
The same rule applies to all types of witnesses, including experts, per R. v. Karaibrahimovic:
7 … Cross-examination of a witness about whether the witness’s testimony in previous proceedings was rejected or disbelieved is irrelevant and ought not to be permitted….
8 Sound policy reasons exist for not using a present trial as an opportunity to assess, or reassess, a witness’s evidence in another, unrelated trial. The most obvious problem is that what happened in the first trial, including the reasoning of the trier of fact in that trial, would not be known to the trier of fact in the second….
11 …The rationale for the collateral evidence rule, that is to avoid mini-trials within trials on collateral issues, applies with equal force to cross-examining experts about the treatment of their testimony in prior cases.
Many other cases say the same thing.
The Ministry of the Environment knows this is the law, and they should follow it.