A killer who hacked off his boss' head while she was still alive claims he was unfairly convicted because the judge failed to remind the jury what had driven him to it. On September 5 last year, dim sum worker Zeng Liang-xin, 31, was sentenced to life in prison for murdering his boss, Wong Miu-kuen. Defence barrister John Mullick yesterday argued that if the trial judge had given the jury more detailed directions, Zeng might have been convicted of the lesser charge of manslaughter by reason of provocation. Zeng claimed Wong, 37, had gone to his Tai Po staff quarters, stripped off her clothes and demanded that he make love to her. He said she threatened to accuse him of rape if he refused. The cook claims she hit her head on an iron bed post as he pushed her away. Believing she was dead, Zeng panicked, hacked off her head and chopped her into pieces. Forensic evidence showed she was probably still alive when he decapitated her on October 30, 1995. Mr Mullick told the Court of Final Appeal yesterday that Mrs Justice Verina Bokhary should have reminded the jury that Zeng was a Chinese migrant worker whose contract had expired. He had already made arrangements to return to his family on the mainland. A rape allegation would have been investigated by Hong Kong authorities, trapping him in the territory. The misdirection warranted a full hearing before the Court of Final Appeal, Mr Mullick argued. He asked the judges for leave to appeal the case. Chief Justice Andrew Li Kwok-nang, Mr Justice Henry Litton and Mr Justice Charles Ching reserved judgment. The three judges will also decide under what circumstances applicants must ask the Court of Appeal for permission to go before the Court of Final Appeal.