The case is one of three crime cases relating to the Saudi gems theft that has strained Thai-Saudi relations for more than two decades.
The move follows Prime Minister Yingluck Shinawatra's appointment in August of a joint panel to oversee the investigations into the three cases.
The committee is chaired by Deputy Prime Minister and Foreign Minister Surapong Tovichakchaikul with Justice Minister Pracha Promnok as his deputy.
The three cases are the theft of gems belonging to the Saudi royal family by a Thai employee in 1989, the murders in 1989 and 1990 of four Saudi diplomats in Bangkok, and the disappearance in 1990 of Mohammad al-Ruwaili who lived in Thailand at the time.
According to a highly placed source at the Department of Special Investigation (DSI), the probe into the disappearance of Mr Ruwaili stalled after a key witness in the case went into hiding.
Pol Lt Col Suwichai Kaewphaluek, who is believed to have been involved in the alleged kidnapping and detention of the businessman, fled overseas after he was sentenced to life in prison in connection with the murder of Lao dissidents.
The source said the joint committee has checked on the whereabouts of Pol Lt Col Suwichai, a retired police officer, and discovered he is in hiding in a neighbouring country. It is considering two options to obtain his testimony.
"One is to have him extradited to testify but the law doesn't allow for a bargain. The other is to send the DSI investigators and public prosecutors over to question him but Thai authorities need permission to do so," said the source.
The source said that in this case, Thai authorities would be subject to a charge of negligence of duty if they questioned Pol Lt Col Suwichai without also arresting him, as he is a convicted man.
Cambodia is a known refuge of a number of convicted Thai felons and the source said Lt Col Suwichai might have chosen this country as his destination.
Five police officers have been implicated in the disappearance of Mr Ruwaili including former Provincial Police Region 5 commissioner Pol Lt Gen Somkid Boonthanom. They served at the Metropolitan Police Investigation Division at the time of the alleged offences.
The five, who face charges of illegally detaining Mr Ruwaili, his premeditated murder, and disposing of his body to cover up the crime, have denied any wrongdoing.
The Saudi businessman reportedly got involved in the gems theft case a year after the heist by Thai worker Kriangkrai Techamong who stole the items from a Saudi palace in 1989.
Mr Ruwaili reportedly had information about the stolen items. The Saudi man disappeared in Bangkok after being interrogated by police in charge of investigating the theft and the officers are believed to be behind his disappearance and probable killing.
Diplomatic relations between Thailand and Saudi Arabia soured after the theft and have steadily deteriorated since, especially in the wake of the killings of four Saudi diplomats.
An attempt to get the diplomatic relationship back on track was made in September this year when Foreign Minister Surapong met Saudi Arabian Vice-Minister of Foreign Affairs HRH Prince Abdulaziz bin Abdullah bin Abdulaziz on the sidelines of the United Nations General Assembly in New York.
This was the first time in 21 years that Saudi Arabia has agreed to hold official bilateral talks with the Thai government.
A Foreign Ministry source said yesterday that if diplomatic relations between Thailand and Saudi Arabia were normalised, both countries could work together again. Thailand would be able to send back its labourers to work in all sectors of Saudi Arabia, said the official.
The source said Saudi Arabia also could allow Thai investors and businessmen to invest in all economic sectors, especially the energy sector. The source added that diplomatic relations would also get back to normal. Thailand would be able to return its ambassador to Saudi Arabia while Saudi Arabia would send its ambassador back here.