Current and former CIA and Justice Department officials who have firsthand knowledge of the interrogation files contend that criminal convictions will be difficult to obtain because the quality of evidence is poor and the legal underpinnings have never been tested.

Some cases have not previously been disclosed, including an instance in which a CIA operative brought a gun into an interrogation booth to force a detainee to talk, said officials.

Other potentially criminal abuses have already come to light, including the waterboarding of prisoners in excess of Justice Department guidelines, and the deaths of detainees in CIA custody in Afghanistan and Iraq in 2002 and 2003.