It follows that the convictions must be set aside and a new trial ordered. Partly because of that, it is necessary to refer to another ground of appeal which it was sought to add at the hearing of the appeal: see Jones v. The Queen [1989] HCA 16; (1989) 166 C.L.R. 409. It was that the trial judge had refused to permit counsel for the appellant to cross-examine Det. Sgt. Muirson about what he saw of the conduct of a man named Brendan O'Brien at or shortly after the police arrived at the house at 343 East Street on the morning in question. O'Brien was the president of the Rebels Club who, on reaching the scene of the shooting, attempted unsuccessfully to wrest a firearm from a police officer evidently with a view to retaliating against the appellant. By that time, however, the violent conflict was at an end, and the police were sufficiently in control of affairs to restrain O'Brien and to remove the appellant out of harm's way. It was nevertheless submitted that counsel for the appellant at the trial ought not to have been prevented from cross-examining O'Brien with a view to eliciting evidence of his aggressive behaviour towards the appellant. It is, however, difficult to appreciate what possible relevance his attitude on that occasion could have had to the matter of the appellant's claim under s.271(2) to have been defending himself against the earlier assault, by three other persons, to which O'Brien was not a party and during which, when it happened, he was not even present.