A BLACKMAILER tried to rid himself yesterday of a judge he claimed was protecting the key witness against him. Ng Yuk-ki, 31, asked Judge Sweeney to step down from his case at the District Court after the judge banned identification of a tycoon. But the judge said Ng wanted the ban lifted to apply pressure to his wealthy victim, and refused his request. It was in the public interest to protect witnesses, he said, because it encouraged others to come forward. Ng had denied a charge of blackmail with menaces but was found guilty on November 16. He appeared yesterday for sentencing and the judge jailed him for 18 months. But his sentence was half what it might have been, after prosecutor Michael Poll submitted a police letter praising Ng for providing information which helped capture other suspects. 'The police need all the help they can get in the fight against crime,' the judge said. Ng met the tycoon in 1982. Thirteen years later, on March 28, he strode into his victim's Wan Chai office and demanded $1 million. He claimed the tycoon owed him about $45,000 from their first meeting and now he wanted the money to set up a restaurant in Shenzhen. Ng threatened to kill the businessman if he failed to come up with the cash. On April 20, Ng appeared at the office again, this time with another man. The blackmailer found his wealthy victim in the lobby with two associates. When they got into a taxi, Ng jumped in behind them. He warned the tycoon that if he reported the incident to the police 'everything will be disclosed', but the tycoon told the taxi driver to take them to Wan Chai police station.