Mr Justice Alan Wright in the Court of First Instance ruled Wu Chun-sing's police statement was inadmissible because of doubts about whether it was given voluntarily.

Mr Wu pleaded not guilty to conspiracy to blackmail and criminal damage.

He accused police of assaulting, threatening and offering him inducements to extract the statement, in which he admitted having a role in the plot.

Mr Justice Wright said he rejected the assault claim but was unable to dispel beyond doubt the accusations of threat and inducement because police had failed to videotape the interview or get Mr Wu's agreement to proceed without a video recording.

A police source, outside court, said the case was rare because interviews were usually videotaped. Station sergeant Chung Kam-wa, chairman of the Junior Police Officers' Association, said it was recommended officers taped interviews.

There were also inconsistencies in the testimony given during the pre-trial process by the officers involved in Mr Wu's arrest and interview. The judge said he therefore had no choice, but to acquit Mr Wu who was immediately released.

On Tuesday, brothers Liu Huihuang and Liu Huizhi pleaded guilty to conspiracy to blackmail, assault occasioning bodily harm, theft and criminal damage. They will be sentenced on August 10. Another two men have been remanded to stand trial on similar charges.

It was alleged Mr Wu was part of a plot to steal the body of Li Chong Yuet-ming, late wife of Mr Li, from a tomb in the Buddhist Cemetery at Cape Collinson on the night of January 29 last year and then ransom it back to the tycoon.

On Tuesday, the court heard that Liu Huihuang told police his part in the plot was to carry out the excavation. He and his elder brother had been recruited by the alleged ringleader to hire several mainlanders for the scheme. They were each to earn several hundred thousand dollars.

Liu Huihuang told police eight people were involved, five mainlanders and three Hongkongers. They had made several dry runs.

On the night in question they were mid-way through the break-in when caretakers returned. Liu Huihuang said he, his brother, Mr Wu and the ringleader confronted the caretakers, a married couple, on the pretext of chasing up a debt.

He had hit the husband with a beef knife, splitting his head open. They took the couple back to their quarters and tied them to a chair.

Liu Huihuang said they had been told to steal the couple's property when they realised they would not be able to break into the tomb. Damage to the tomb was estimated at HK$51,600. The brothers were arrested on December 11.