NINE alleged members of a triad gang which terrorised Boston for 12 years have been arrested hours after the suspected dragonhead was detained in Hong Kong. Stephen Tse Chun-on, 49, nicknamed Skydragon, was stopped by immigration officers at Lowu while trying to cross into China yesterday afternoon. He had $150,000 with him. He will appear in Eastern Court today at a hearing to determine whether he should be extradited to the US. Those arrested in Boston are believed to include Tse's wife Angela. Tse was arrested on a warrant issued in Hong Kong based on documents from America alleging he conspired to commit murder. The FBI alleges that Tse is the dragonhead of the Ping On triad in Boston. A series of raids by more than 100 FBI officers at about 25 premises in Boston took place to coincide with the arrest. Tse was born in Hong Kong, but was granted US nationality six years ago. Since then he has spent most of his time in the territory. He had a flat in Taikoo Shing. Two months ago, Tse was acquitted in Hong Kong of possessing triad writings. The Boston arrests, the biggest strike in Massachusetts against the triads, follow on the heels of a string of operations against Chinese organised crime in New York. Since September, federal and local agents have arrested alleged leaders and enforcers from three leading triad gangs - the Fuk Ching, White Tigers and Tung On. Sixteen alleged Ping On members have been indicted on charges of attempted murder, running illegal gambling houses, extortion, bribing police officers and holding illegal firearms. US agents were last night still hunting six of them. Tse, 44, formerly of Braintree, Massachusetts, has been charged with four other men with complicity in the shooting in Boston in 1988 of two rival Ping On gang members, allegedly to boost their position in the gang. The 17-count indictment against the 16 defendants states: ''The enterprise [the Ping On] acted to protect itself by intimidation, violence and threats of violence against other criminal groups and individuals which it perceived as a threat to its territory. ''Within its territory, the enterprise attempted to maintain its control by engaging in multiple acts of intimidation and extortion of both legal and illegal businesses.'' According to the indictment, the Ping On had an extensive network designed to obtain leaks from inside the Boston police force about potential law enforcement activity against it. The charges follow a long-running joint operation between the FBI, immigration agents and Boston police.