Thai law enforcement authorities announced Thursday that they will file murder charges against former Prime Minister Abhisit Vejjajiva and his deputy in the first prosecutions of officials for their roles in a deadly 2010 crackdown on anti-government protests.

The protests and crackdown left more than 90 people dead and about 1,800 injured in Thailand's worst political violence in decades. Abhisit's Democrat Party, ousted in elections last year, and "red shirt" supporters of the ruling Pheu Thai Party have blamed each other for the bloodshed since.

Department of Special Investigation chief Tharit Phengdit said Thursday that investigators found Abhisit possibly culpable in the death of a taxi driver because he allowed troops to use war weapons and live ammunition against protesters.

Abhisit and former Deputy Prime Minister Suthep Thaugsuban, who was in charge of the ad hoc security agency set up to contain the protests, will be summoned to the DSI office on Dec. 12 to be formally charged. Abhisit is currently leader of the opposition as head of the Democrat Party.

The courts must accept the case before it can go to trial.

Democrat Party spokesman Chavanond Intarakomalyasut called the decision "an abuse of government's power to threaten its opponents." He noted that it was done while parliament is in recess so the two men's immunity from arrest is lifted.

Tharit denied that the decision is politically motivated and said the case is significant "for society because the deaths were inflicted by an act of government officers."

The deaths occurred during the red shirts' nine-week anti-government protest in the heart of the capital that had sought to force Abhisit to call early elections. Central Bangkok was garrisoned by soldiers until they moved in to crush the protest on May 19, 2010.

The protest was staged primarily by supporters of former Prime Minister Thaksin Shinawatra, who was ousted by a 2006 military coup after being accused of corruption and disrespect to the monarchy. His supporters and opponents have vied for power since then, and Thaksin's sister Yingluck Shinawatra was elected prime minister last year.

A Criminal Court inquest recently found that taxi driver Phan Kamkong was killed by guns used by military personnel during the crackdown.

Chavanond alleged that the inquest was a one-sided trial in which the accused could not defend themselves, and added that no one was pinpointed as the shooter.

He insisted the security body set up to contain the protests issued no order to use force against or kill civilians, only to keep order in dealing with "black shirts," armed men who served as guards for the demonstrators.

"To use the court's inquest to conclude that the two men had the intention of murder was groundless and against the law," Chavanond said.

He said both Abhisit and Suthep "are ready to prove their innocence," and that "those who brought up false charges will have to take responsibility."

DSI chief Tharit said factors leading to the planned charges include the continuing use of force over an extended period of time, and the killing of civilians without resorting to other methods of controlling protesters.