NEW YORK -- The legal basis for the FBI's past use of emergency requests to obtain telephone records should be kept secret, the Justice Department said in a court filing last week.

The Justice Department has admitted that the issuing of those "exigent letters" was a mistake. But now it is fighting to keep the reasoning by which its Office of Legal Counsel approved such use under wraps. Critics argue that continues a degree of increased secrecy begun in the George W. Bush administration around the influential OLC memos, which in practice often set government policy on matters like drone killings.

The FBI improperly made use of the exigent letters hundreds of times from 2003 to 2006 to gain access to records about phone calls, although not their actual contents, the Justice Department's inspector general found in a 2010 report. But even after the inspector general began his investigation, the OLC wrote a secret memorandum suggesting that the letters could sometimes be legally justified.

In its filing before the U.S. Court of Appeals for the D.C. Circuit, first reported Friday by Legal Times, the Justice Department argued that OLC legal memos are protected by exemptions from public records requests and that releasing them would "chill deliberative discussions within the Executive Branch."

The Electronic Frontier Foundation filed a lawsuit in May 2011 seeking to gain access to the exigent-letter memo. In a September 2012 decision, a U.S. district judge ruled that the government could keep it hidden, accepting the government's argument that it was an internal deliberation and thus exempt from disclosure requests under the Freedom of Information Act (FOIA).

Finding out what that memo said, and why, is crucial to the public's understanding of what happened with the exigent letters, said Elizabeth Goitein, co-director of the Brennan Center for Justice's Liberty and National Security Program. Since 9/11, she wrote in an email, the government has increasingly relied on the secret legal memos to justify dubious or outright duplicitous departures from the laws.

"When the law that the executive branch is following (the OLC opinion) says something entirely different than the law on the books (the statute), it becomes extremely important that the OLC opinion be made public," Goitein said. "Otherwise, the public is not merely in the dark -- it is affirmatively misled about what laws are in effect."

The Justice Department has argued, time and time again, that it can keep the memos secret because they are simply internal deliberations, a category exempted under FOIA. The Obama administration refuses to reveal even the number of these legal memos.

OLC memos have also been a major issue in the fight over the Obama administration's secrecy around targeted drone killings, and the Bush administration sparked controversy for years by refusing to release memos giving its legal justification for torture.

The OLC's memos "function essentially as the law of the executive branch," said Anne Weismann of Citizens for Responsibility and Ethics in Washington, which has filed a friend-of-the-court brief in the Electronic Frontier Foundation case urging their disclosure. "The notion that the executive branch and the Justice Department can keep them secret at will I think is a very frightening idea."

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