THE Court of Appeal yesterday upheld the conviction of a teenager who murdered his 13-year-old girlfriend in a fit of jealous rage and set fire to her body after she told him she had an affair with another youth. The court, comprising Vice-President Sir Derek Cons, Mr Justice Nazareth and Mr Justice Litton, was satisfied that the summing up of the trial judge was a fair presentation of the case to the jury trying Cheung Ka-man. Cheung, now 18, was found guilty last August of the murder of Lam Pui-yu. As he was under 18 at the time of the killing, Mr Justice Bewley ordered him to be detained at Her Majesty's pleasure. It was the Crown's case that Cheung was an attentive but jealous and possessive boyfriend. A few days before she was killed, Pui-yu found a new boyfriend whom she went out with on January 28, 1991. She did not return to her Tuen Mun home until 2.20 am the next day and five hours later, she was found lying on a staircase with the upper part of her body badly burned. The cause of death was strangulation. Cheung did not deny killing Pui-yu but denied murdering her, claiming that he was provoked into strangling her after she confessed to having a sexual relationship with someone else. Cheung was represented by Mr Graeme Mackay. Senior Crown Counsel Mr Darryl Saw appeared for the Crown.