Retired prosecution chief Grenville Cross has rounded on the "hands-off" approach taken by the man currently in the post towards the ICAC's 18-month investigation of former chief executive Donald Tsang Yam-kuen.
In a media letter, Cross, director of public prosecutions from 1997 to 2009, said Kevin Zervos should wrap up the case before he retires on September 8.
Zervos hit back by saying that the Independent Commission Against Corruption's investigation of Tsang was "near completion" and describing Cross as "out of touch".
Cross wrote: "It is exactly 1½ years since Donald Tsang's case was first referred to the ICAC, and there has still been no announcement by the Department of Justice on whether or not he will be prosecuted, which is incredible.
"It is damaging to the standing of the legal system, which is supposed to ensure that criminal investigations are processed expeditiously and do not simply disappear into outer space."
Tsang was embroiled in several scandals before his term ended last year. He admitted enjoying two holiday trips on private jets and two on yachts while in office. He also failed to declare plans to lease a Shenzhen penthouse from mainland tycoon Bill Wong Cho-bau at a bargain rent.
Cross drew comparisons with recent investigations involving Executive Council members - Barry Cheung Chun-yuen's case took three months to clear, while that of Franklin Lam Fan-keung took nine months.
"The DOJ [must now] be proactive and adopt a 'hands-on' approach, and not simply sit back and twiddle its thumbs until something happens," added Cross, honorary professor of law at the University of Hong Kong.
More worryingly, he argued, Zervos would leave many undecided cases to his successor, Keith Yeung Kar-hung. These include former ICAC commissioner Timothy Tong Hin-ming, development minister Paul Chan Mo-po, and Chief Executive Leung Chun-ying.
"It would not be right to expect Yeung to have to handle Tsang's case as well."
Calling Cross' remarks "astonishing", Zervos said there was no need to speed up the ICAC's work and he had been "in communication with" the graft-busters. "[Progress] should not be determined by whether someone is about to retire or not. If it takes 18 months, it takes 18 months."
Zervos said that the ICAC's cases were under the scrutiny of its operations review committee, an independent body. He stressed that the spirit of criminal justice was proceeding with cases "properly and thoroughly", especially as Tsang's case involved outside jurisdictions.
Zervos said Cross was "ill-informed". "He's out of touch and out of date with our criminal justice system ... Grenville doesn't know what the case involves."
Avery Ng Man-yuen, vice-chairman of the League of Social Democrats who reported the case in February last year, said he had received no update on the case from the ICAC.
An ICAC spokesman would only say that investigation work was under way.