Wang Qishan (center), a member of the Standing Committee of the Political Bureau of the Communist Party of China (CPC) Central Committee and secretary of the CPC Central Commission for Discipline Inspection, addresses a conference on the work of central-level Party inspection in Beijing, China, Feb 11, 2015. [Xinhua]

More than 200 million yuan ($31.23 million) in cash, all covered in dust with some damaged, was found in Liu Xiangdong's house, former head of the disciplinary inspection team of Northern China's Shanxi province, according to some media reports. And that was only part of the booty, the reports said.

The astonishing amount of money and his special position both have made Liu the central figure among the four corrupt officials named by Central Commission for Discipline Inspection of Communist Party of China, the country's top disciplinary watchdog, over the weekend.

The case raises a key question: Who will supervise the supervisors? In the nationwide crackdown on corruption, the country's top leadership and provincial disciplinary committees have sent inspection teams to supervise officials in powerful lower-level departments. As representatives of higher authorities, the members of such teams are generally more powerful than the departmental officials they investigate. But that also makes it possible for the investigative officials to become part of the corruption racket. How to supervise the members of such investigation teams to make sure they stay clean?

The question deserves special attention, because corruption within the disciplinary watchdog is much more damaging than that in any other Party or government department, simply because it challenges the credibility of those fighting corruption.

An article on the official website of the Central Commission for Discipline Inspection says Liu's discipline violations deeds include revealing inspection teams' secrets. Details of the information Liu revealed are not known, but they could include the clues for suspected corruption cases. Inspection team leaders and members might know the indicting facts against many corrupt officials, and by trading those with the suspects, they could undermine the fight against corruption.

The CCDI leadership has been emphasizing the importance of supervision of inspection teams. That's why it selects the best and most honest inspection team members from among the disciplinary commissions and other Party and government departments to conduct inspections.