Democrat leader Abhisit Vejjajiva and the party's MP for Surat Thani Suthep Thaugsuban Monday testified to the Department of Special Investigation over the crackdown on the red-shirt rallies.
They were both confident they demonstrated that they had acted legally.
The two men, who were in charge of directing state measures against the demonstrators, are accused by the red shirts of involvement in the 91 deaths of protesters and soldiers, most of which took place during clashes at the Khok Wua and Ratchaprasong intersections in April and May 2010.
Mr Abhisit recalled the events Monday while he was questioned by DSI investigators for up to seven hours, as the officers wanted him to check his testimony.
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"I based my clarification on facts," Mr Abhisit said.
The former prime minister, who arrived with documents relating the events in chronological order, explained what his government did from its initial responses to the protesters to its decision to crack down on them.
"There's no worry at this stage," he said, referring to the DSI's ongoing investigation into the deaths.
The fatalities occurred once the rally turned more violent, with shooting and arson attacks later taking place both in Bangkok and upcountry.
On April 6, 2010, during the lead-up to the violence, Mr Abhisit, then the prime minister, addressed the public through a TV broadcast that his government would stick to the country's laws and policies of tolerance in dealing with the red-shirt demonstrators.
Among its first measures, the government sent officers to the rally venue to tell protesters the gathering was illegal, Mr Abhisit said.
However, the demonstrators, under the leadership of the pro-Thaksin United Front for Democracy against Dictatorship which demanded the Abhisit administration dissolve the House for new elections, continued rallying and brought about disorder, he said.
Some red-shirt co-leaders violated the emergency decree to break into the parliament compound while some supporters caused the evacuation of patients at Chulalongkorn Hospital during their raid to search for soldiers believed to be hiding there, he said.
Mr Suthep, then deputy prime minister and director of the Centre for the Resolution of the Emergency Situation (CRES), helped Mr Abhisit handle the rally, but was later viewed by some people as a "plaintiff" in the event.
However, looking back at the CRES measures against the protesters, Mr Suthep is confident the actions were considered carefully by CRES members.
"I'll tell only the truth," Mr Suthep said before testifying to DSI investigators yesterday.
"I think I have an advantage because I took note of what everyone said and argued in each meeting," he said.
DSI chief Tarit Pengdith was asked by reporters whether he also needs to provide his account of events to investigators because he was also a CRES member.
He said he did not as he was only a state official who "never joined the [CRES] meeting on strategic planning".
Mr Suthep submitted 200 pages of documents and CRES minutes to the DSI as evidence yesterday.
He chose to reserve his opinion when asked whether he is confident about the outcome of the probe and about his response to Mr Tarit's claim, except to say that "Mr Tarit stayed with me then and gave useful suggestions".