Last year, the National Security Agency (NSA) reviewed all of Edward Snowden's available emails in addition to interviewing NSA employees and contractors in order to determine if he had ever raised concerns internally about the agency's vast surveillance programs.

According to documents the government filed in federal court Friday, NSA officials were unable to find any evidence Snowden ever had.

In a sworn declaration, David Sherman, the NSA's associate director for policy and records, said the agency launched a "comprehensive" investigation after journalists began to write about top-secret NSA spy programs upon obtaining documents Snowden leaked to them. The investigation included searches of any records where emails Snowden sent raising concerns about NSA programs "would be expected to be found within the agency." Sherman, who has worked for the NSA since 1985, is a "original classification authority," which means he can classify documents as "top-secret" and process, review, and redact records the agency releases in response to Freedom of Information Act (FOIA) requests.

In his declaration, Sherman detailed steps he said agency officials took to track down any emails Snowden wrote that contained evidence he'd raised concerns inside the agency. Sherman said the NSA searched sent, received, deleted emails from Snowden's account and emails "obtained by restoring back-up tapes." He noted that NSA officials reviewed written reports and notes from interviews with "NSA affiliates" with whom the agency spoke during its investigation.

"This includes affiliates who contacted the organization in response to a June 10, 2013 message to all Agency civilians, contractors, and military personnel with NSA email accounts asking anyone who had contact with Mr. Snowden to report those contacts to" the Associate Directorate for Security and Counterintelligence, which conducted its own, separate "exhaustive searches."

Still, the agency says it did not find any evidence that Snowden attempted to address his concerns internally — as he has said he did — before leaking the documents.

The NSA disclosed these new details about its investigation into Snowden in response to a FOIA lawsuit VICE News filed against the NSA earlier this year seeking copies of emails in which Snowden raised concerns about spy programs he believed were unconstitutional.

Sherman's declaration states:

As part of this investigation, the Agency collected and searched all of Mr. Snowden's email available on NSA's classified and unclassified system. This included sent, received, and deleted email, both in his inboxes still on the networks and email obtained by restoring back-up tapes from Agency networks. Multiple members of the Associate Directorate for Security and Counterintelligence read all of the collected email.

Additionally, given that organizational designators appear for each NSA sender and recipient for email transmitted on NSA's classified and unclassified systems, searches of Mr. Snowden's collected email also were done using the organizational designators for the offices most likely to have been recipients of any email written raising concerns about an NSA signals intelligence program.

Those offices included the NSA's Office of General Counsel, the Office of the Comptroller, and the Signals Intelligence Directorate Office of Oversight and Compliance. Moreover, Sherman said, the NSA tasked the Office of General Counsel, the Office of Inspector General, and the Office of the Director of Compliance to "search for communications to or from Mr. Snowden in which he may have raised concerns about NSA programs."

"The search did not identify any email written by Mr. Snowden in which he contacted Agency officials to raise concerns about NSA programs," Sherman wrote.

The government asked the judge to dismiss the FOIA case.

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The email issue surfaced following an interview Snowden gave to NBC News last May, when Snowden said that before he leaked documents to journalists Glenn Greenwald, Barton Gellman, and Laura Poitras, he first raised concerns through "internal channels" and was told "more or less" to "stop asking questions." Lawmakers, intelligence officials, and even some journalists had previously pilloried Snowden for not first approaching NSA officials and members of congressional oversight committees about the surveillance programs that caused him concern.

The NSA's response to Snowden's claims was swift. The agency publicly released a single email Snowden sent to the NSA's general counsel in April 2013 in which he raised a question about NSA legal authorities in training materials.

"I actually did go through channels, and that is documented," Snowden told NBC News's Brian Williams during the interview in Moscow. "The NSA has records, they have copies of emails right now to their Office of General Counsel, to their oversight and compliance folks, from me raising concerns about the NSA's interpretations of its legal authorities."

The NSA's response to Snowden's claims was swift. The agency publicly released a single email Snowden sent to the NSA's general counsel in April 2013 in which he raised a question about NSA legal authorities in training materials.

"The email… poses a question about the relative authority of laws and executive orders — it does not register concerns about NSA's intelligence activities, as was suggested by Snowden in an NBC interview this week," said Senator Dianne Feinstein, the chairwoman of the Senate Intelligence Committee, after a copy of the email was turned over to the committee last April.

Snowden, who the government's court documents say worked on contract for the NSA Threat Operations Center, fired back at the NSA in a lengthy statement that called into question the agency's search:

Today's release is incomplete, and does not include my correspondence with the Signals Intelligence Directorate's Office of Compliance, which believed that a classified executive order could take precedence over an act of Congress, contradicting what was just published. It also did not include concerns about how indefensible collection activities — such as breaking into the back-haul communications of major US Internet companies — are sometimes concealed under [Executive Order] 12333 to avoid Congressional reporting requirements and regulations.

If the White House is interested in the whole truth, rather than the NSA's clearly tailored and incomplete leak today for a political advantage, it will require the NSA to ask my former colleagues, management, and the senior leadership team about whether I, at any time, raised concerns about the NSA's improper and at times unconstitutional surveillance activities. It will not take long to receive an answer….

According to Sherman, the Signals Intelligence Directorate's compliance office was searched and Snowden's colleagues searched their own email accounts as well. The communications Snowden claims he sent did not turn up.

Sherman described the type of search the agency conducted to locate the emails Snowden says he sent. The NSA's search of its own emails is limited to "person by person" as opposed to bulk searches, the agency said in response to a FOIA request filed by ProPublica last year.

As Sherman said in his declaration:

Using an email alias (i.e., a group email address that sends messages to all Office of General Counsel personnel), the Office of General Counsel tasked its personnel to do a search of their individual email for email to or from Mr. Snowden in which he may have raised concerns about NSA programs. The Office of Inspector General conducted an advanced search of its Inspector General Management Information System (IGMIS), using the phrase 'Snowden' as a search in the 'Contact Last Name' field…. This system documents complaints and grievances filed with the Agency's Office of Inspector General. The Office of the Director of Compliance tasked its personnel to search official email, web-based contacts, and correspondence for any evidence that Mr. Snowden contacted the personnel or the Office of Director of Compliance 'for any reason.'

The NSA official said no emails that fit this description were located. Sherman said additional searches were conducted in Hawaii, where Snowden last worked. A search was also done at the Threat Operations Center, Snowden's division, for any emails he forwarded in which he raised concerns.

"If there was any email written by Mr. Snowden to raise concerns about NSA programs, that email most likely would have been located in Mr. Snowden's inbox, which includes sent email, or in his email restored from backup tapes. No such email was found," Sherman's declaration says. "The NSA searched everywhere such an email would reasonably be expected to be found, if it existed, including the account from which it would have been sent and back-ups of that account, as well as offices to which such an email could be expected to have gone."

Ben Wizner, Snowden's attorney at the American Civil Liberties Union, told VICE News he has not had in-depth discussions with Snowden about the emails his client says he sent, and therefore cannot respond to the government's claims. Wizner said the issue of Snowden's emails is "somewhat of a red herring" since "Snowden witnessed an entire regime of surveillance and what was needed was not for higher-ups to be aware of his concerns, but for the public to be brought into the conversation."

Wizner said he believes there is evidence to be found backing up Snowden's claims. But he added:

"Where it is, I don't know."

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