The Constitution Court has ruled that evidence obtained from the United Arab Emirates,where a key witness in the 1990 disappearance of a Saudi Arabian businessman fled, is against the constitution and so invalid in court.
The ruling could be a setback to prosecutors who need information from the witness, their last one.
The decision followed a complaint made to the court by Pol Lt Gen Somkid Boonthanom, a retired police officer and defendant in the alleged kidnapping and detention case of Saudi businessman Mohammad al-Ruwaili, who disappeared in Bangkok in 1990.
On Feb 4, the Criminal Court approved a request by prosecutors to question Pol Lt Col Suwitchai Kaewphaluek, suspected of being involved in the Ruwaili case but under witness protection by the Department of Special Investigation (DSI).
Pol Lt Col Suwitchai is believed to have fled the country after receiving a life sentence for another murder case. An arrest warrant was issued for him in 2009.
Late last year, however, Lt Gen Somkid told the court that Pol Lt Col Suwitchai had changed his name to Kiatkorn Kaewphetsri and now lives in the UAE.
DSI chief Tarit Pengdith later admitted the department took Pol Lt Col Suwitchai to the UAE as part of its witness protection programme. Since Thailand and the UAE have no extradition agreement, Pol Lt Col Suwitchai has not been arrested there.
Once prosecutors learned about his whereabouts, they sought permission to send a team to question him in the UAE.
The Criminal Court, however, ruled in a 5-4 vote on Wednesday the use of evidence acquired without the defendant having an adequate right to verify it or argue against it would violate his constitutional rights.
Criminal Court Chief Justice Tawee Prachuaplarb said the court's executives will have to consider the ruling and see how it would proceed with the case.
Special case prosecutor Ruj Khuensuwan said the prosecution was trying to gather as many facts as possible. He said Pol Lt Col Suwitchai is the prosecution's last witness. If he can't be brought to testify, defence witnesses will take their turn at the stand. Defendant Lt Gen Somkid said he has prepared about 10 witnesses.