The police commissioner defended the force's record on escapes from custody yesterday and announced an investigation into how a Vietnamese illegal immigrant managed to flee from a Mongkok police station on Saturday. Dick Lee Ming-kwai said the inquiry would look into possible negligence and flaws in procedures for handling suspects, as well as facilities and security at the station. 'If it finds there are things that need improving, we would improve them,' Mr Lee said. But given the huge number of arrests made in a year - more than 10,000, he said - having one 'problematic case' was 'not surprising'. The 27-year-old man was detained on Friday, in possession of other people's identity cards, and was discovered to be missing from the Playing Field Road police station at about 11.30am on Saturday. Police speculated he might have slipped out while relieving himself or hid himself among a group from the same cell when they were escorted out for medical checks.