OFFICERS probing the killing of ICAC witness Tommy Chui To-yan have arrested a seventh person in Hong Kong as the investigation in China continues to focus on the major suspect's transfer to Singapore. Police said a 22-year-old woman was arrested at Kai Tak airport on Wednesday. It was not clear whether she was planning to travel or was waiting to meet somebody when she was detained by officers attached to the Organised Crime and Triad Bureau. It is understood the woman's arrest was linked to the questioning on Monday of four men and two women in relation to Chui's murder in Singapore in late March, and their suspected affiliation with the Wo On Lok triad society. Each has since been released without charge. Talks concerning the extradition to Singapore of the main suspect, Johnny Cheung Wai-ming, continued in Beijing yesterday. The search was also continuing for three men, believed to have been in Kunming, but who may now have fled. The body of Chui, 38, a businessman involved in cigarette trading, was found near Clifford Pier in Singapore partly weighed down by diving belts. His mouth was taped and it seemed he had been abducted after having his Porsche forced from the road and taken to a car park. He was the principal witness for the Independent Commission Against Corruption case in an alleged $8.5 billion cigarette smuggling case.