A POLICE chief inspector bled to death yesterday after being shot in the chest and held hostage for almost three hours by one of his own officers. A sergeant entered the inspector's office at the Castle Peak divisional station for an interview at 3 pm. Officers heard a gunshot at 3.35 pm from the room occupied by an Assistant Divisional Commander, but when they tried to enter found the sergeant had locked the door and was threatening to commit suicide. Tuen Mun District Commander Ronald Clibborn-Dyer made contact with him and began negotiating for him to surrender. Officers of the Special Duties Unit, which handles commando-style operations, set up a monitoring post in a building opposite the station, with a view of the second-floor office. The inspector, 43 and married with two daughters, was slumped over his desk. The uniformed sergeant, 47, was seen standing with his back to the door, but it was not clear whether he was holding a weapon. At first it was decided not to attempt to force the door open because of the sergeant's suicide threat. But at 6.20, the armed Special Duties Unit was sent in and they arrested the sergeant without firing a shot. The inspector was taken to Tuen Mun Hospital but was certified dead an hour later. Senior Superintendent Martin Cowley, who is leading the investigation, said: ''It is too early to speculate on what happened but we have arrested a man and he is helping us with our inquiries.'' The suspect, who was also treated for hand injuries, was escorted away from the hospital by officers of the Regional Crime Unit. Police refused to release the inspector's identity as some relatives had not been informed.