The top policeman overseeing a mysterious department responsible for tracking, eavesdropping on and finding crime suspects has been put under investigation for divulging state secrets, bribe-taking and keeping a mistress, according to a mainland media report. The online version of Beijing-based Caixin Magazine said that Zhang Jian, 58, the head of the Operation and Technology Bureau under the Public Security Ministry, was placed under shuanggui - a form of detention imposed exclusively on officials within the Communist Party by the party's Central Commission for Discipline Inspection. The exposure of Zhang's possible downfall came after Chen Shaoji, the former top police officer in Guangdong, was given a suspended death sentence last Friday for taking about 30 million yuan (HK$34 million) in bribes. Zhang is at least the third police official detained this year for alleged involvement in corruption. This case involved two departmental deputies as well. The deputies - Li Jingfeng, deputy chief of the ministry's petition office, and Lu Shan , 46, deputy head of the information centre for the Science and Technology Bureau with the police force - were also detained and placed under investigation for suspected corruption. The disciplinary commission has transferred their cases to the country's legal department. The report said news of Zhang's detention had circulated within the Public Security Ministry as early as July 15. Zhang was under suspicion of having been involved in a string of crimes and of having a degenerate lifestyle, including leaking state secrets, a serious economic problem (a common euphemism for corruption), patronising prostitutes and keeping a mistress. The report added that the internal notice issued on July 15 also mentioned that Zhang was implicated by two of his subordinates when the latter were investigated. Boasting the most advanced hi-tech devices, the bureau headed by Zhang was in charge of tracking, wire-tapping and locating suspects in cases investigated by other bureaus in the ministry. The report also said that Zhang's bureau each year used hundreds of millions of yuan to locate and buy the most updated equipment, a common hotbed for corruption. Given the sensitive nature of the department, details about it - such as its structure and personnel - have not been made public despite the transparency policy championed by the State Council in recent years.