A police officer who infiltrated a triad gang for 11 months in one of Hong Kong’s most dangerous undercover operations, leading to the arrest of 299 gangsters , is now allowed to carry a pistol to guard against revenge, sources say. Force insiders revealed on Wednesday how the officer was tested by gang leaders in the final months of the operation, singing songs to him from films such as the hit Infernal Affairs , an undercover police drama, to check his response. A brief history of Hong Kong’s triad gangs They said the officer now weighed only 41kg after losing 13kg during the 11-month sting, which ended with a major crackdown. Hundreds of police officers raided suspects’ homes and unlicensed venues in the New Territories, starting on Monday night. The revelation came as four suspected triad bosses arrested in the operation were released on bail to allow police more time to gather evidence and seek legal advice. How Hong Kong triad members get paid as little as HK$200 to terrorise neighbours to force debtors to pay A Yuen Long district councillor and three alleged Yuen Long faction leaders of the Wo Shing Wo triad were among those nabbed this week. A senior police source close to the investigation described the sting as one of the longest and most dangerous undercover operations in a decade. The mole, in his mid-20s after graduating from police college a few years ago, had to assume a false identity as a vulgar hooligan to go deep undercover. He detached himself completely from his family and friends, starting from the bottom and working his way up to eventually earn the trust of the gang leaders and collect solid evidence. We believe they have identified him as the mole. He is worried rival triad gangsters will attack him A police source “He has now returned to the force and is on leave. He is entitled to carry a pistol with him all the time to protect himself,” the source said. “We believe they have identified him as the mole. He is worried rival triad gangsters will attack him.” His colleagues could not recognise the officer after the assignment as he looked completely different after losing so much weight, the source added. Another senior police insider said the gang leaders often tested the mole by using various tactics, such as threats, to see if he was a snitch. Triad leader jailed two years after being caught by undercover cops identifying himself at party “While drinking, they talked about the fate of undercover police officers in movies to test his response. They even sang songs from movies such as Infernal Affairs to test him,” the source said. “He knew the force would take action very soon. Any mistake would strike a fatal blow to our plans, his long-term efforts and also his own safety. You can imagine how stressful it has been.” The source said it was up to the officer to decide if he needed 24-hour police protection and live in a safe house. He would no longer do frontline work in the New Territories to minimise exposure. Former Hong Kong triad member reflects on his life from gangster to rehabilitation worker “He can also request psychological consultations and decide how long he needs to be off from work. It is not easy to adjust in many ways when he returns to normal life.” Top brass were said to be full of praise for the undercover policeman and were most likely to promote him. The source explained that such undercover operations usually did not last longer than six months to avoid jeopardising officers’ safety.