An illegal immigrant who tried to rob a prostitute received the most lenient sentence available yesterday when the judge cast doubt on the credibility of two prosecution witnesses. Ho Tung-man, 26, cried with relief after Deputy Judge Peter White gave him an absolute discharge. Judge White said he was concerned by the evidence and credibility of the prostitute, Cheung Sau-lin, and her boyfriend. But Ho was jailed for 12 months after admitting illegally remaining in Hong Kong. He denied attempted robbery but was found guilty. Simon Tam, prosecuting, told the District Court Ho went to Cheung's flat in Tsuen Wan on January 14 and paid $200 for sex. He then tried to rob Cheung but her boyfriend rushed in. Cheung, 34, was jailed on Wednesday for 20 days for handling stolen goods. She had previous convictions for soliciting and assault. Her boyfriend was given a suspended sentence for theft and using a false instrument.