AN illegal immigrant already serving 15 years for kidnapping was yesterday sentenced to a further 16 years. Tsang Kam-cheong, 32, had pleaded guilty to manslaughter, wounding, aggravated burglary and robbery. Passing one of the longest sentences ever imposed, Mr Justice Ryan said that to protect the public it was necessary to remove Tsang from society for a long time. The judge had sentenced Tsang last Wednesday for kidnapping a 28-year-old teacher, robbery, possession of an imitation firearm and theft. Senior Assistant Crown Prosecutor Samuel Leung said that on August 18 last year Tsang burgled a flat in Beacon Road, Kowloon. During the robbery he threatened the couple living there with what appeared to be a pistol. Tsang stabbed Ip Ching-hung in his bed, despite the pleading of his wife, Chan Yuen-yee. He then stabbed Ms Chan as she tried to support her husband, who had fallen off the bed. Tsang fled after taking $1,000 and a watch. Ip, 46, was dead on arrival at hospital - he had been stabbed in the heart. Ms Chan had five stab wounds in her stomach, arm and back. When arrested, Tsang said he only intended to rob the couple, but Ip put up a struggle. He said he had killed Ip by mistake. On July 8 last year, Tsang robbed Lau Hang-yung, a lecturer at the Chinese University, and his wife at their staff quarters. Tsang demanded money from them, tied them up and ransacked the room, taking about $7,000 and valuables. Tsang's fingerprints were found at both locations. When Tsang was arrested on November 14 he was wearing Ip's watch. His counsel, Paul Dinan, said the only mitigating factor was Tsang's plea. The judge said that although Tsang's plea mitigated the crime, the evidence against him was very strong. He said he would sentence Tsang to seven years for burglary, 16 years for manslaughter, 10 years for wounding and eight years for robbery. This would give a total of 41 years, which with the 15 years he was already serving would mean 56 years. ''Even for someone as dangerous as you, that's too long,'' the judge said, ordering the first three sentences to run concurrently, and half of that 16 years to run concurrently with the existing 15-year jail term.