A prisoner involved in a robbery in which a policeman died was found hanged from a torn sheet in his cell yesterday. Lam Wai-kong, 32, was jailed for 20 years in June 1992 for a robbery in which his accomplice shot a policeman dead. The mainlander was found hanging from window rails in Shek Pik Prison on Lantau at 1.43am by prison guards. He was unconscious. A Correctional Services Department spokesman said Lam was given first-aid before being airlifted to Queen Mary Hospital. He was pronounced dead at 3.17am. The illegal immigrant was arrested when he and three other mainlanders robbed a hotpot restaurant in Temple Street of $9,222 in December, 1990. His accomplice, Yu Lok-ting, shot dead Constable Tang Siu-tung during the robbery. In June, 1992, Lam was given 20 years' jail while Yu was sentenced to death, commuted to life imprisonment. The other two accomplices, Law Chung-yiu and Law Sin-chi were jailed for 16 and 19 years respectively.