I don't know if that's entirely correct, and I beg to differ in this respect. The judgments say they won't rely on the other judgment as the basis for the finding in their case. I'm reasonably confident I'm correct in this: for the crowns in Ciarniello--that's the second Ontario case, Justice McMahon's decision--and then there was the Kirton case, the one in the Manitoba Court of Appeal, the issue was whether or not in the Kirton case in Manitoba they could rely on Justice Fuerst's finding in the Lindsay and Bonner case. There was no suggestion that the crown in Kirton had done the right thing, which the Criminal Code allows. The crown does this all the time for other expert opinion evidence.
It doesn't mean that the defence isn't allowed to cross-examine, but the judge has the discretion as to whether or not to permit that kind of cross-examination, and the judge can demand from the defence this: what's the reason you're insisting that I drag the crown's expert on gangs all the way to my court when they were cross-examined? You can read it in the transcript that has been provided to me, counsel. Why would I allow you to ask the same questions again?
It's very rare that an expert's credibility is the issue. It's always the credibility of the science. So it just hasn't been used.
I'll say one last thing. It's because the crown thinks it's their duty to present the evidence again, and they haven't tried doing this. I'm sorry, but I beg to differ with your characterization.