Thailand's prime minister has said a Muslim human rights lawyer who went missing in 2004 may have been killed by government officials.
A policeman has been jailed for illegally detaining the lawyer
PM Thaksin Shinawatra also said that an ongoing investigation into Somchai Neelaphaijit's disappearance suggested more than four officials were involved.
A court on Thursday jailed one policeman but acquitted four others for illegally detaining Mr Neelaphaijit.
The lawyer's wife Angkhana and human rights groups denounced the verdict.
Mr Neelaphaijit was last seen at a Bangkok hotel in March 2004, and rights groups fear he was killed because of his criticism of police conduct in the south of the country, where there is an ongoing Muslim insurgency.
Mr Thaksin said that prosecutors would file a new case, possibly as soon as next month.
Home to most of Thailand's 4% Muslim minority
Muslim rebels fought the government up to the mid-80s
Suspected militants have upped attacks this year, targeting Buddhists
Security forces' response criticised by rights groups
He said a special team from the Department of Special Investigation (DSI) was now working on murder charges, based on circumstantial evidence gathered since the original trial began.
"I know that Somchai is dead, and more than four government officials were involved, but witnesses and evidence are still being collected," Mr Thaksin was quoted as telling the French news agency AFP.
None of the suspects at the first trial were tried for murder, only illegal detention and robbery.
Mr Thaksin did not say if the new charges would be filed against the same people as before, or against other government officials.
Somchai Neelaphaijit's disappearance and his subsequent trial have put Thailand's treatment of human rights under the spotlight.
Rights groups maintain that the 52-year-old lawyer was kidnapped and killed by police officers, because of his vocal criticism of the Thai security services' handling of the unrest in the south.
The authorities in southern Thailand are battling a long-running insurgency by Islamic separatists, which has led to the deaths of more than 1,000 people in the past two years.
In the months before his disappearance, Mr Neelaphaijit had defended Muslim suspects in connection with violence, and went missing soon after claiming some of his clients had been tortured.