A businessman acquitted of a $167 million robbery at Kai Tak airport in 1991 is wanted for questioning by police investigating the recent spate of prison attacks. But Cheung Tze-keung, 39, is believed to be in China. And a top illegal road racer, Jim Cheong-shing, 39, was among 24 people arrested on Wednesday. Detectives of the Organised Crime and Triad Bureau arrested one more man yesterday. The arrests included ex-prisoners and triad members. On Wednesday, two air pistols, $2 million in cash and items such as spray paint, clothes and shoes were seized for matching as a footprint and banners painted with protest slogans were found at the scene of the attacks. Sources said there were about four key suspects in the case. Police are establishing the link between the gang and the four people arrested at The Peak in early May when Molotov cocktails were found in a Mercedes-Benz. A source said the attacks were believed to be related to grievances of some of the ex-prisoners. 'There is no indication that they have paid the other people for the attacks,' the source said. Cheung has faced two trials and spent a total of three years in custody as a result of events arising out of the $167 million raid at Kai Tak airport. He was acquitted in June last year because the judge said the identification evidence against him was unreliable. However, Cheung has pleaded guilty to being in possession of a stolen Portuguese passport and was sentenced to 12 months' imprisonment suspended for two years and ordered to pay a fine of $50,000. Jim had convictions for illegal road racing, and possessing arms and ammunition without a licence. In the first prison attack on April 18, a crane was used to demolish a sentry post at Stanley prison. Six days later, several men used a dump truck to destroy a sentry post at Siu Lam psychiatric centre. Banners were found at the scene of the attacks, protesting against the use of sedatives on prisoners. On April 27, a can of paint thinner was found under the burned-out wreck of a Correctional Services superintendent's car, outside Stan-ley prison's residential quarters.