A suspect's confession made during police questioning could simply be reversed during the court trial.

Moreover, if the judges have any doubt over the prosecution's indictment or testimony by state witnesses, "then the benefit of the doubt will be given to the defendant, meaning acquittal or the dropping of a trial", he said.

Police Maj-General Winai Thongsong, commander of the Crime Suppression Division, responded to Sombat's comments by saying police were still gathering evidence and working on other witnesses.

"We are not only relying on Sgt-Major Chakhrit Janthara's confession and implication against other suspects," he said.

Chakhrit was questioned yesterday for the first time since he underwent the re-enactment of the attempt on Saturday. He remained subdued when asked by reporters to comment on a recent statement by former Internal Security Operations Command deputy leader General Pallop Pinmanee that he was too "loony" to carry out such a high-profile plot.

A police source said investigators would not probe further into the possible involvement of Maj-General Surasak Iamraksa, head of the internal security service at the Isoc, although police recently searched his home for possible evidence.

Surasak is unlikely to be linked to the car bomb plot as he was a Class 10 colleague of Thaksin Shinawatra at the Armed Forces Academy Preparatory School, the source added.