The Independent Commission Against Corruption has long been one of Hong Kong's most cherished institutions, credited with helping turn the city from one of Asia's most corrupt into one of its cleanest.
The impact of the ICAC after its foundation in 1974 was such that, 30 years later, former police chief Dick Lee Ming-kwai said: "The speed with which syndicated corruption was eradicated has few parallels in the history of law enforcement."
But the graft-buster has faced an unprecedented crisis of credibility in recent weeks amid revelations of lavish spending on entertainment by former commissioner Timothy Tong Hin-ming, raising the question of whether there are enough checks and balances on the ICAC.
To put it another way: who watches the watchdog?
Tong is accused of splashing out on gifts, receptions and duty trips during his tenure between 2007 and 2012. Some of the expenses exceeded limits but were approved by Tong himself. What's more, some of the expenses were not reported to the Legislative Council.
Chief Executive Leung Chun-ying has created a review committee to examine Tong's spending and the regulations on official spending on entertainment. Two Legislative Council committees will also investigate the case.
Current and former ICAC investigators say they are disappointed and angry at Tong's actions and hope the public will distinguish between Tong's activities and the graft-buster's 39-year record of cleaning up the city.
"This has affected the ICAC seriously - in terms of staff morale and its credibility, built up over 39 years," said Tony Kwok Man-wai, a former deputy commissioner who served as a graft-buster for 27 years.
The power structure of the ICAC is designed to keep abuse in check.
The body is directly accountable to the chief executive, while the ICAC commissioner must report to the Executive Council on major policy issues. The commissioner is also answerable to Legco on policy and funding matters.
There are four advisory committees, with members appointed by the chief executive, to oversee the work of the ICAC, as well as a complaints committee that monitors and reviews all non-criminal complaints against the ICAC or its staff.
But the Tong affair reveals that the power of the commissioner - especially on approving expenses - depends much on the anti-graft tsar's self-control.
Legislator Regina Ip Lau Suk-yee, for whom Tong worked when she was secretary for security, expressed sadness and disappointment at the Tong affair.
The Executive Council member and New People's Party chairwoman said the fact the ICAC reported to the chief executive, rather than reporting to a bureau, as with other government departments, could be problematic.
"I can't imagine the chief executive would have to be responsible even for vetting daily expense claim forms submitted by the ICAC commissioner," she said.
Commissioner Simon Peh Yun-lu said he was open to the idea of reporting regularly on expenses to the chief executive. But, he said: "Normally the chief executive is very busy and may not have time to take care of such trivial matters. But if he makes such a request, I can report to him."
Kwok also said it would not be a problem if the commissioner approved his own expenditure.
"In any system there should be a certain amount of trust ... It would be too bureaucratic [if department heads have to seek approval from bureaus]," he said. "Should a man with a [big salary] have to seek approval from the chief executive if he spends a little bit more when eating? It is a bit over the top."
Questions have also been raised about the commission's record in cleaning up its own organisation.
Democratic Party chairwoman and legislator Emily Lau Wai-hing cited a past example of graft-busters investigating one of their own. Former principal investigator Raymond Yuen was arrested in April 2011 over corruption-related offences. But Lau said so far there had not been any news on the progress of Yuen's case.
The commission's internal investigation and monitoring unit, L Group, investigates all allegations of corruption and related offences made against ICAC staff.
Democratic Party member and former ICAC investigator Lam Cheuk-ting is confident his former colleagues will handle the Tong probe fairly.
Tong's troubles started when an audit report last month revealed details of two lavish dinners he hosted and approved for mainland officials. The average spending per head was more than HK$1,000, well above the permitted HK$450.
Legco papers later revealed that Tong had spent HK$220,000 on gifts during his five-year tenure as anti-corruption chief, of which more than two-thirds was spent on presents for mainland officials. He also spent HK$757,921 on 34 duty trips, 19 of them to the mainland.
Later, local media reported that Tong had hosted at least 20 receptions with officials from the central government's liaison office, and claimed that the details of other spending running into hundreds of thousands of dollars had yet to be revealed. Bowing to public pressure, the commission admitted Tong had spent about HK$48,000 on biscuits and mooncakes and promised to comprehensively review all of its spending.
The scandal also revealed that there was no regulation governing gift-giving within the ICAC. Peh has pledged to work on such a rule.
Lam says no single system can completely prevent abuse. But in the long run the four advisory committees should enhance their regulatory powers and the transparency of the ICAC's administration.
He agreed the HK$450-per-head ceiling for hospitality was enough and if there was a need for exceptions the commissioner should seek it from one of the committees, or at least inform it.
Lawmaker Dr Joseph Lee Kok-long, who also sits on the ICAC operations review committee which monitors and scrutinises ICAC investigations, doesn't believe there is a need for another agency to monitor the ICAC.
He agreed the allegations against Tong might have threatened the commission's integrity. "But they are still allegations, not proof," he said. "If we set up another body to monitor ICAC work, it may have an impact on the independence of the ICAC."
Lee added: "It may not be totally accurate to say the ICAC is unchecked. It reports to the chief executive and the chief executive is supposedly responsible for monitoring its work. If the chief executive does not do so, it is the chief executive's problem.
"The chief executive could report to the Legislative Council regularly on what he has done to monitor the ICAC and answer lawmakers' questions."
The Audit Commission and Legco's public accounts committee could also monitor how the ICAC used its money, Lee added.