TWO serving police officers have been questioned by anti-triad detectives in connection with the contract killing of suspected gangster Hui Hau-yee. The officers, both constables believed to be serving in the Marine Police, were ''interviewed'' by the Organised Crime and Triad Bureau (OCTB) last week after they were linked to a car used by the killers in last Monday's shooting. OCTB spokesman, acting Superintendent So Kam-sing, confirmed the men were questioned, but said they were not charged and back at work. The men, whom he did not identify, ''clarified some points'' about the vehicle, a Toyota Cressida, which was reported stolen from Tai Po a few days before the shooting. ''The car used by the two criminals is under the registration of a serving police officer, but there is no indication to link the two officers to the shooting,'' Mr So said yesterday. One of the policemen sold the car to the other officer but the registration remained in the former's name, he added. But it is the fact the Toyota's keys were still in the ignition when it was abandoned that led detectives to ask the officers just how the killers obtained a set of keys. After the vehicle was reported stolen, the two hitmen removed the genuine registration number and fitted false plates to the Toyota. Hui, 34, is reputed to have been a member of the Fuk Yee Hing triad and first came to Hong Kong as an illegal immigrant from China in the 1980s. Although he did not have a criminal record, detectives believed he started as a street hawker and then became involved in smuggling Chinese antiques into the territory before progressing to other criminal activities. Over the last few years he set up at least three development companies in Hong Kong with mainland links, specialising in million-dollar land deals in southern China. Police believe a dispute linked to one of these deals could have led to Hui's death. They understand he had been in China trying to settle a dispute on the day he was killed and are keen to interview his mainland business contacts. Detectives are believed to have given details of a business colleague of Hui to Public Security Bureau officials in Shenzhen. Police believe the attackers were waiting for Hui and a ''friend'', believed to have been his bodyguard, when they arrived back in Hong Kong from China. They left the KCR station in Mongkok by taxi when it was stopped by the killers at about 9.30 pm on Luen Wan Road. The two hitmen opened fire and Hui, who managed to stagger 50 metres down the road, collapsed when he was hit in the head. No attempt was made to shoot his friend Cheng Kwong-ngang. According to an autopsy report, Hui was hit four times, although the gunmen, both believed to be locals, fired at least 10 rounds at him from close range. Mr So said a ballistics report confirmed two guns, both believed to be 7.62 mm Red Star pistols, were used. Cheng, 39, was arrested after the discovery of a pistol and ammunition hidden inside a soft toy at a Tsuen Wan laundry where his girlfriend worked.