Winai did not disclose details of the three witnesses, saying only that he would seek the permission of the Military Judge Advocate for an investigation of them.

He said police needed to investigate the three witnesses before they were brought to the Military Court for fear they would flee under the impression their lives were at risk.

Meanwhile investigators yesterday found that three knives confiscated from Lt-General Manas Sukprasert's houses earlier this week bore traces of copper electrical wire. Officials said the evidence was consistent with information collected from witnesses who said the Daewoo sedan involved in the alleged plot had been seen in Manas's car-care centre in Suphan Buri before Lieutenant Thawatchai Klinchana was arrested with it. Officials believe that the bomb may have been assembled in one of Manas's houses in Suphan Buri.

Police are looking for others involved in assembling the bomb.

Sgt-Major Chakhrit Janthara, a prime suspect who has been detained by the Crime Suppression Division, has still not received a visit from any of his relatives.