In this case information had not been disclosed to the defence, and had it been disclosed the conduct of the case for each side would have been different. Therefore, non-disclosure here went to the question of trial fairness .
The question of trial fairness is not answered by considering what verdict the appellate judges would have reached at a hypothetical trial :
The case illustrates how an appellate court should apply this test. At trial the prosecution had alleged that the defendant's guilt of his wife's murder was demonstrated by her rings that could only have been found where they were if he had removed them from her corpse. The non-disclosed evidence was that the rings had been at that location before she died.
Non-disclosure significantly affected the course of the trial. This was not a case of freshly discovered evidence, although I think the difference should be immaterial because the ultimate question is whether there is a real possibility that the omission affected the verdict.
I have suggested that all conviction appeals raise issues of trial fairness. This is because a fair trial is one where the law is properly applied to facts that are determined impartially. "Impartially" is used in a wide sense to include actual and apparent bias as well as inaccuracy. Even appeals challenging jurisdiction raise fairness in this sense, as without jurisdiction the law is not properly applied. Fresh evidence appeals also concern fairness, as the newly discovered evidence may demonstrate a real possibility that the verdict was wrong. There can be unfairness even if the verdict was not affected, where the law was not properly applied, but this was not that sort of appeal.
I have recently (7 April 2011) mentioned misuse of hypotheticals by appellate courts, and have also criticised the usurpation of the jury role by appeal judges, for example here (9 July 2009) and here (25 June 2007), and here (16 January 2006).