My criticism of the New Zealand Supreme Court's majority decision in Morgan v R can now be assessed in the light of a correct approach by the Supreme Court of Canada to the use of a jailhouse informer's evidence in R v Hurley  SCC 18 (14 May 2010).
In Hurley the cell mate claimed that the accused had confessed to him that he had cleaned the crime scene in an effort to remove evidence of his participation; in particular, he had attempted to remove all traces of his DNA.
One of the requirements of the warning that must be given to the jury in such cases (this in Canada is called the Vetrovec warning, after R v Vetrovec  1 SCR 811) applies where reasons to doubt the reliability of a witness may not be self-evident to the jury:
"something in the nature of confirmatory evidence should be found before the finder of fact relies upon the evidence of a witness whose testimony occupies a central position in the purported demonstration of guilt and yet may be suspect by reason of the witness being an accomplice or complainant or of disreputable character..." (Vetrovec, per Dickson J, para 42).
See also my discussion of R v Khela  SCC 4.
In the circumstances in Hurley, supporting evidence for the cell mate could only be evidence that the crime scene had been cleaned. There was no issue that the accused had been at the scene, but he gave an innocent explanation for that, so presence of some of his DNA would not be conclusive. This is encapsulated in para 7 of Hurley (Mr Niemi is the cell mate):
"The evidence about the attempts to clean the room was unquestionably significant to the Crown's case. In his closing address, Crown counsel submitted to the jury that, on the evidence before the court, it was "clear that there was an attempt to clean the room" ... . The evidence of attempts to clean the room could be taken as independent evidence tending to support Mr. Niemi's evidence about his conversation with Mr. Hurley. In turn, Mr. Niemi's evidence supported the Crown's case that Mr. Hurley had not only been there, but also that he was the killer. Thus anything that tended to rebut the room cleaning theory tended to weaken the independent evidence that could be seen as supporting Mr. Niemi's version of the conversation with Mr. Hurley and, consequently, weakened the Crown's circumstantial case."
There was fresh evidence concerning the finding of Mr Hurley's DNA at the crime scene – this evidence was not available to the Court of Appeal – and the Supreme Court ordered a new trial. This evidence made it unnecessary for the Court to address the seriousness of criticism of the trial judge's Vetrovec warning, which was that the jury had not been told sufficiently why they might have reservations about the credibility of the cell mate's evidence of the accused's confession.
Hurley brings into focus the need for precision as to what evidence is capable of supporting, or undermining, the reliability of the contested evidence. Whereas in Morgan the New Zealand court majority judgment was imprecise on this (and precision would have revealed that there was no such supporting evidence), in Hurley the Canadian court highlights the supposedly supportive evidence and concludes that a second jury might not think it was as strong, in the light of the fresh evidence, as it had seemed.