Former attorney-general Chulasingh Vasantasingh on Friday denied he was protecting Thaksin Shinawatra in deciding not to prosecute him on terrorism charges, a decision that drew widespread criticism.
Mr Chulasingh, who retired on Sept 30, spoke out on the issue for the first time in an appearance before a House subcommittee.
He argued the issue was beyond the authority of the Office of the Attorney-General as the nature of the case was outside Thailand.
"The issue went beyond the kingdom's boundary, and therefore it was beyond authority of the Office of the Attorney-General,'' he told the panel on political development and mass media at parliament.
Mr Chulasingh said it was difficult to take action against people outside Thailand for inciting terrorism. He insisted his decision was fair with no intention to favour any particular faction.
"If a leader shouts from other countries and those inside don't want to do it, they won't,'' he told the panel, indicating that Thaksin had no influence on the rally against the government in 2010 when the Democrats were in power and Abhisit Vejjajiva was prime minister.
"I think I did the right thing,'' he added.
His decision to drop the indictment aganst the former prime minister was kept secret until he retired on Sept 30 , and then confirmed by his successor, Athapol Yaisawang, on Thursday, after Democrat MP Thaworn Senneam broke the news days earlier.
The OAG's decision rejected the recommendation of Department of Special Investigation chief Tarit Pengdith to take action against Thaksin.
The allegations centred on Thaksin's video calls to red-shirt United Front for Democracy against Dictatorship protesters in Bangkok and other provinces during their increasingly violent rally to oust Mr Abhisit and his government in April-May 2010.
The demonstration ended in more violence following a military crackdown, with many private and government buildings being set on fire by rampaging mobs, including major shopping malls.
The charges also involved 25 other red-shirt protest leaders besides Thaksin, including Maj Gen Khattiya "Seh Daeng'' Sawatdiphol, the organiser of the red-shirt guards who was shot dead by a sniper and the charge subsquently voided.
The court cases related to these chagres are continuing.
The OAG separated the Thaksin case from the others on grounds that he was overseas .
"I am a bit surprised at his explanation. It seems to me that the OAG used different standards for Thaksin from from the others who were indicted,'' Mr Abhisit told the Democrat Party's Bluesky channel.
The opposition leader said he was confident about Thaksin's involvement in the turmoil, given his role during the demonstrations, despite his being outside the country.
Government deputy spokesman Pakdiharn Himathongkham welcomed the OAG decision, saying Thaksin never incited the protesters to violence. His messages were to "promote democracy'' and oppose military coups, he added.
Thaksin fled the country in 2008 before the Supreme Court's Criminal Division for Holders of Political Positions sentenced him to a two-year jail term for abusing his authority as prime minister in the purchase of state land by his then wife in the Ratchadaphisek area. He mainly stays in Dubai, but spends a lot of time in China.
The opposition party on Friday asked visiting Chinese Prime Minister Li Keqiang not to let Thaksin use China as a base for political operations.
Democrat list-MP Watchara Phetthong said that Thaksin had been using Skype to communicate with supporters of the red-shirts.
"Prime Minister Li Keqiang should not let this fugitive escape to China and use the country as his political headquarters and issue orders to [his people] in Thailand," Mr Watchara said.