Observers were surprised at the inclusion of the charge as it had been speculated that only less serious charges including possessing explosives would be filed against the Internal Security Operations Command (ISOC) officers following the September 19 coup.

Police will submit their investigation report and indictment suggestions to public prosecutors on Monday after a two-hour meeting to wind up their part of the case yesterday.

The four suspects are Maj-General Phairoj Theerapharb, Colonel Suraphol Supradit, Lt-Colonel Manas Sukprasert and Lieutenant Thawatchai Klin-chana.

The officers all face six charges: criminal conspiracy to commit premeditated murder; attempting to kill a state official on duty; possessing explosives; having non-authorised items in their possession; forging and using official documents; and criminal conspiracy.

Sgt-Major Chakhrit Janthara, an ISOC officer whom police said was charged with identifying the target and obtaining a Daewoo sedan that carried a large amount of explosives and a blasting agent, would not be charged in exchange for turning state's evidence to implicate the four officers.

According to the police investigation report, Phairoj was the leader of the team, Suraphol coordinated the operations and obtained the Daewoo sedan and Manas was in charge of explosives and detonation.

Thawatchai was arrested while driving the sedan near the former premier's Bang Phlat residence on August 24.