An office of the CIA has admitted that it "mistakenly" destroyed its only copy of an extensive 6,700-page classified report on torture prepared by the Senate Intelligence Committee, it was reported on Tuesday (17 May).

A CIA official privately told the federal Department of Justice and the Senate Intelligence Committee about the snafu in the summer of 2015, saying that the CIA's office of inspector general (IG) — the agency's internal watchdog — accidentally destroyed both the disk holding the entire report and the file uploaded on agency's servers.

The official, acting Inspector General Christopher Sharpley, said the IG's office would obtain a new copy from the CIA, but that has not happened yet and may never happen.

"It's breathtaking that this could have happened, especially in the inspector general's office – they're the ones that are supposed to be providing accountability within the agency itself," Douglas Cox, a City University of New York School of Law professor told Yahoo News, which broke the story. "It makes you wonder what was going on over there?"

California Senator Dianne Feinstein, the driving force behind the 2014 report, apparently sent letters to the CIA and Justice Department confirming that the spy agency's inspector general "has misplaced and/or accidentally destroyed" its copy of the report. Feinstein has written to CIA Director John Brennan, asking him to give the IG's office a fresh copy.

"Your prompt response will allay my concern that this was more than an 'accident,'" she wrote. "The CIA IG should have a copy of the full study because the report includes extensive information directly related to the IG's ongoing oversight of the CIA."

It's possible that the deletion of the report is part of a wider strategy to release its findings to as few people as possible. The CIA retains a copy of the full classified report, but is apparently awaiting the conclusion of an ongoing legal battle over the document before any other copies are distributed.

The episode is humiliating for the CIA inspector general and has inflamed human rights advocates who are hoping to make the report public. The full report remains classified, although a 500-page executive summary was released into the public domain.

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Cori Crider, a director with Reprieve, called the IG's deletion of the report "stunning," and suggested that it is part of a broader effort to erase torture practices from history.

The report has itself had a tortuous history. It was written after the CIA admitted in 2007 that it destroyed videotapes of waterboarding detainees. Feinstein sent a copy of the full report to the White House and other arms of government in late 2014 when the executive summary was released to the public.

But Senator Richard Burr later called back copies from the executive branch in a bid to keep it in the hands of the Senate Intelligence Committee, which is exempt from having to release documents under the Freedom of Information Act, according to the Hill.

The Justice Department has been bolstering Burr's efforts. It has told agencies not to open the report's file, presumably to prevent it from coming under the scope of the Freedom of Information Act.

A federal appeals court panel recently blocked an effort to reveal the full report under the open records law, claiming that it "always has been a congressional document."

According to Yahoo News, the appeals court was not notified that the inspector general's copy of the report was destroyed.