Police are investigating whether a brutal chopping attack in Cheung Sha Wan last week that left one of five knife-wielding gangsters dead was carried out on the orders of a former leader of the Wo On Lok triad. An initial investigation showed the 36-year-old attacker who was gunned down by a traffic policeman on Friday was a Wo On Lok member and a henchman of its ex-leader, known as Ko Lo Fat, a police investigator said. Ko Lo Fat and two fellow senior members of the triad known as 'Fei Wai' and 'Sam Chuen' were among six suspects arrested on Saturday, police said. The six men, aged 22 to 56, were not among the attackers, but were the key figures behind the chopping assault on a faction leader of Wo On Lok, a 45-year-old who went by the name of 'Fei Kai', police believe. The six were released on bail last night as more time was needed to find the attackers and collect evidence, the investigator said. 'We believe the attack was sparked by long-standing infighting between two factions in a leadership struggle in the Wo On Lok triad society.' The triad elects leaders every two years. The infighting is understood to have begun after Fei Wai and Sam Chuen refused to step down in 2010, sparking a row with two other gangsters, Chi Fung and Dai Ma. Fei Wai and Sam Chuen are believed to be more henchmen of Ko Lo Fat, who supports their continued leadership. Ko Lo Fat was injured in an ambush by 10 people during an outing with his wife and two sons in Wan Chai in February. The investigator said Friday's assault was the latest of eight retaliatory attacks. Yesterday afternoon, the parents and relatives of the dead gangster held religious rites at the spot where he was shot, burning paper offerings and joss sticks. It was during the attack at the junction of Pratas Street and Castle Peak Road at about 9.30pm that the traffic policeman fired one shot and hit the gangster. The attackers had ignored repeated warnings and threatened to hack the officer who was less than two metres away, police said. The gangster died in hospital, while the other four escaped. It is understood police identified one of the four attackers, nicknamed 'Siu Ping', who fled on foot and left his identity card at the scene. A senior police officer said frontline officers were on alert for possible retaliation. 'If necessary, we will raid entertainment venues controlled by the triad,' he said. The Wo On Lok, also known as Shui Fong, operates mainly in Sham Shui Po, Mong Kok, Tsim Sha Tsui and Yau Ma Tei.