At least a dozen detectives from the same police station were questioned yesterday in connection with a blackmail case and some were still being held late last night. Police acknowledged the existence of the investigation but would say nothing more. 'The police have received a complaint alleging that police officers were involved in an intimidation and blackmail case,' a spokeswoman said last night. 'Kowloon West regional crime unit is now following up the case and the probe is continuing.' Officers from the unit were understood to have gone to Mong Kok police station yesterday afternoon and take about a dozen police away for questioning. Sources said the officers questioned were all of junior rank, the most senior being sergeants, and came from the station's crime investigation division support team. It was not known how many of them were actually implicated in the blackmail case or how many were still being held at Kowloon West divisional headquarters last night. The case is believed to involve officers blackmailing suspects in deception and intimidation cases in which they do not have enough evidence to proceed against the suspects, sources said. Questioning of such a large number of officers has been rare in recent years. Meanwhile, officers from the narcotics bureau seized drugs worth about HK$2.8 million during a raid in a village at Wop Hop Shek. They stopped a man, 26, outside a house in Wo Hing Tsuen at about 1pm and found more than 3kg of Ketamine on him. The officers found another 11.5kg of Ketamine inside the house. Later, in another flat in Wo Hop Shek Tsuen, they found 2.2kg of cannabis. The man has been arrested for drug trafficking and was detained for questioning overnight.