The billionaire Kwok brothers returned to the ICAC yesterday to renew their bail conditions in the city's biggest-ever corruption case. Thomas Kwok Ping-kwong and Raymond Kwok Ping-luen, co-chairmen of SHKP, along with Rafael Hui Si-yan, the former Hong Kong chief secretary, briefly attended the graft busters' headquarters in North Point yesterday morning. They were arrested in March by the Independent Commission Against Corruption after an investigation into allegations of bribery and misconduct in public office. Ousted chairman Walter Kwok Ping-sheung and SHKP executive director Thomas Chan Kui-yuen also reported back to the ICAC in the afternoon. Chan was among the first to be arrested, in March, while estranged brother Walter Kwok was arrested earlier this month. All five must report back again in early July. Market watchers continue to monitor the effect the investigation is having on the shares of one of the city's biggest developers. The stock dipped to an intraday low of HK$86.50 yesterday before rebounding to close at HK$88.20, slightly up on Friday's close. The price has dropped 20.61 per cent since the first two brothers' arrests on March 29. Alfred Lau, an analyst at Bocom International, said: 'When will the corruption investigation come to an end? How long will it remain unclear whether the ICAC will lay charges? Such questions will not be answered in the short term.' The South China Morning Post understands the unprecedented probe relates to the former chief secretary's long-standing relationship with the Kwok brothers; allegations of more than HK$100 million in debt linked to Hui; a flat he rented from Sun Hung Kai; and irregular land deals. The ICAC needs more time to investigate and has been consulting the Department of Justice for legal advice. No charges have been laid so far. SHKP said in a statement: 'The company has been advised by its lawyers that it would be inappropriate to comment, as the case is still under investigation.' The negative publicity arising from the arrests hurt SHKP's reputation and prompted Thomas and Raymond Kwok to hire the global crisis management firm APCO Worldwide. A person close to the Kwok family confirmed APCO's hiring. 'The family has been employing a public relations firm, but changed to APCO recently. The newly appointed PR firm came after increasing numbers of media inquiries about the family's issues.' An ICAC spokesman refused to comment on the case.