The Justice Department made public detailed memos on Thursday describing brutal interrogation techniques used by the CIA, as President Barack Obama sought to reassure the agency that CIA operatives who carried out the techniques would not be prosecuted.

Lawyers within the clandestine branch of the Central Intelligence Agency gave written approval in advance to the destruction in 2005 of hundreds of hours of videotapes documenting interrogations of two Qaida lieutenants, according to a former senior intelligence official with direct knowledge of the episode.