Two senior state officials have been allowed to testify to the National Anti-Corruption Commission (NACC) as witnesses for former prime minister Abhisit Vejjajiva and his former deputy Suthep Thaugsuban.
Both men are facing an investigation in connection with the deadly crackdown on red-shirt protesters in April and May 2010.
NACC member Vicha Mahakun said the commission decided to allow the testimony of former army chief Anupong Paochinda and former National Security Council chief Thawil Pliansri as their role during the crackdown was relevant. They are scheduled to appear at NACC headquarters on Tuesday but they may choose instead to submit their statements and any related documents without turning up in person.
Mr Vicha heads the graftbusters' sub-panel in charge of probing the 2010 crackdown. In February 2014, he found Mr Abhisit and then deputy prime minister Suthep Thaugsuban ordered armed forces to disperse peaceful protesters in April 2010 and, failing to adapt their methods, launched another deadly crackdown in May 2010. Ninety-nine people died in the operations.
The Criminal Court conducted autopsies on the victims' bodies and found the wounds were caused by military bullets. The NACC brought charges against Mr Abhisit and Mr Suthep, now a monk, based on the fact the suppression operations they oversaw intensified between April and May 2010. The army's response escalated despite the civilian casualties and the government's knowledge there were peaceful protesters in the crowds, Mr Vicha argued.
In their defence, Mr Abhisit and Mr Suthep said the situation in Bangkok was like that of a war zone rather than a protest. They said armed elements were using military weapons against the authorities during the demonstrations.
Mr Suthep insisted these individuals, the so-called "men in black'', were hidden among protesters and carried out terror attacks. The crowd dispersal methods intensified as a result of those terror activities.
Mr Vicha said graftbusters would ask Gen Anupong and Mr Thawil how they modified their tactics.