A MAN found guilty of taking part in a revenge attack had his murder conviction quashed yesterday by the Court of Appeal. It held that a High Court judge had made a crucial mistake in his summing up to the jury. In allowing the appeal of Chow Kam-sung, and setting aside the mandatory death sentence, the Court of Appeal held it was a proper case for a retrial. But the court, which comprised Mr Justice Litton, Mr Justice Bokhary and Mr Justice Mayo, upheld the conviction of another man, Au Pang-fei, who was also found guilty of murder. Chow, 28, and Au, 34, had denied killing 25-year-old So Ching-tang but were found guilty by a jury before Mr Justice Duffy. It was the Crown's case that the attack arose from a jostling incident involving So at the Apollo 18 karaoke bar in Kowloon on the evening of October 10, 1991. Shortly after midnight, witness Tse Man-fai saw a group of men, many of them armed with knives, chasing So along a street. They finally ran him to the ground in a park nearby, he said. Chow, in his defence, said he was present at the scene but claimed he was not there to encourage the attack but to implore the others not to do it. Chow's counsel, Michael Lunn, on appeal said the trial judge had told the jury Mr Tse had said in his evidence he saw Chow holding a knife. In fact, Mr Tse had not said this. But Senior Assistant Crown Prosecutor Andrew Bruce contended the trial judge was entitled to say that because Mr Tse had testified he recognised Chow as one of the men who chased and chopped So. Mr Justice Bokhary, delivering judgment for the court, pointed out that the witness did not actually see the fatal chopping attack and he said nothing in his evidence to the effect he saw Chow holding a knife. It was a crucial mistake by the judge, he said. It was possible that the mistake would make all the difference between a conviction and an acquittal. In the circumstances Chow's conviction could not stand, the judge added. However, Mr Justice Bokhary held that there was nothing in the case of Au, who was represented by Gerard McCoy, to render his conviction unsafe or unsatisfactory. Asking the court to issue a retrial order for Chow, Mr Bruce said it was a vicious murder and the evidence against Chow was abundant.