US plans to appoint a criminal prosecutor to probe whether CIA interrogators used techniques, including excess waterboarding that were not authorised on terror suspects, a media report said on Sunday.
A top juctice department official said Attorney General Eric H Holder Jr intends to hold an inquiry focussing on "whether people went beyond the techniques that were authorised" in Bush administration memos that liberally interpreted anti-torture laws.
CIA 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, officials said, the Los Angeles Times reported.
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.
Opening a criminal investigation is something Holder "has come reluctantly to consider," the Justice Department official said, emphasising that Holder had not reached a final decision but noting that, "as attorney general, he has the obligation to follow the law."