The US justice department is to launch a criminal investigation into the CIA's erasing of videotapes of interrogations of two al-Qaeda suspects.
The CIA destroyed the tapes while being scrutinised over secret prisons
It follows last month's preliminary joint inquiry with the CIA into whether a full investigation was necessary.
Critics have accused the CIA of a cover-up to hide evidence of possible torture and abuse of detainees.
The CIA says it destroyed the tapes as they no longer had "intelligence value" and were a security risk to its agents.
US Attorney General Michael Mukasey announced the move, appointing federal prosecutor John Durham to oversee the case.
In a statement he said: "The department's national security division has recommended, and I have concluded, that there is a basis for initiating a criminal investigation of this matter."
CIA spokesman Mark Mansfield said the agency would "co-operate fully with this investigation as it has with the others into this matter".
The hundreds of hours of footage, recorded in 2002, reportedly contained images of interrogation techniques including water-boarding, which simulates drowning.
President George W Bush has said that the US does not use torture but has not been specific about interrogation methods.
Congress are also examining exactly how and why the tapes came to be destroyed in 2005.
The House Intelligence Committee has called on Jose Rodriguez, the former CIA official who ordered the tapes destroyed, to appear at a hearing on 16 January.
The Bush administration has so far refused to co-operate with the congressional investigation.