Macau police have arrested a former right-hand man of "Broken Tooth" Wan Kuok-koi a week before the gangster's release from prison.
Chan Yuet-bo, who had been a senior detective with the Macau Judiciary Police, was arrested in a flat in Taipa yesterday afternoon.
About 10 armed officers were involved in the arrest.
Sources said a casino employee who was suspicious his wife having an affair found Chan to hire a hit man from the mainland to murder her.
It is understood that two people who worked under Chan were stopped and arrested when they were following the wife. Officers subsequently arrested Chan, the hit man and the husband.
Sharpened screwdrivers, 20 knives, air guns and explosives were found during the arrest. The men were arrested for organised crime, attempted murder and possession of banned weapons, the source said.
Chan, 66, was sentenced to 10-1/2 years in prison and released in 1999. He was convicted of running a gang and possessing illegal weapons.
His case was concluded two days after the sentencing of Wan, then the 14K triad boss in Macau, to 13 years and 10 months in prison for loan-sharking, money laundering and involvement in organised crime.
Their trials, which took place a month before Macau's handover to China, were regarded as a major victory against the Portuguese enclave's powerful gangsters.
Wan is due to be released on December 2, and is reportedly planning to re-enter the casino junkets business.
The most feared gangster in Macau during the 1990s, he was arrested on May 1, 1998, hours after a bomb failed to kill Judiciary Police chief Antonio Marques Baptista.
Wan's rival Ng Man-sun, the Mong Kok wet market trader turned casino boss who is widely known by the nickname "Street Market Wai'', was attacked by a gang of six men in June as he dined with a woman friend in a restaurant at the New Century Hotel on Taipa.
Security experts said the beating bore the hallmarks of a triad attack.