U.S. officials once disputed NSA contractor Edward Snowden’s claim that he had raised questions about the agency’s domestic surveillance programs before he fled the U.S. with thousands of stolen documents, but now confirm that Snowden sent at least one email about the agency’s practices to officials.

That email was released Thursday, offering the public a deeper look into Snowden’s actions.

The NSA released this Edward Snowden email to the Office of General Counsel asking for an explanation of some material that was in a training course he had just completed, Thursday May 29, 2014. Office of the Director of National Intelligence

In an exclusive interview with NBC Nightly News anchor Brian Williams, Snowden said he had warned the NSA while working as an NSA contractor that he felt the agency was overstepping its bounds.

“I actually did go through channels, and that is documented,” he asserted. “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 response more or less, in bureaucratic language, was, ‘You should stop asking questions.’”

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“I would say one of my final official acts in government was continuing one of these communications with a legal office. And in fact, I’m so sure that these communications exist that I’ve called on Congress to write a letter to the NSA to verify that they do.“

Just six months ago, the NSA told the Washington Post’s Bart Gellman that no evidence of a paper trail existed. “After extensive investigation, including interviews with his former NSA supervisors and co-workers, we have not found any evidence to support Mr. Snowden's contention that he brought these matters to anyone's attention," said the agency in a statement.

On Thursday, however, White House spokesman Jay Carney said the Snowden email would be made public "later today." It was released a short time later by the Office of the Director of National Intelligence.

Before it was made public, two U.S. officials who had read the email sent by Snowden to the NSA’s Office of General Counsel on April 5, 2013, a month before he stopped working as an NSA contractor, told NBC News the message -- the only email found to date, they say -- questioned agency policies and practices.

Snowden sent the April 2013 email to the NSA’s lawyers while on temporary assignment at NSA headquarters in Ft. Meade, Md.

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One U.S. official who had read the email said that in it Snowden asked a question about how the NSA was interpreting its legal justifications for domestic surveillance, and wrote out a hierarchy of U.S. law, with the Constitution at the top. Beneath the Constitution he placed federal statutes, and under them, Defense Department regulations, Office of the Director of National Intelligence regulations, and NSA policy.

Three days later, the NSA’s lawyers responded that he was correct in his analysis of how the NSA justified its collection of domestic data, and said the collection was legal.

The official said that Snowden had asked a question, but had not “raised concerns” about the NSA’s practices.

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NBC News has filed a request under the Freedom of Information Act to find out if there are additional documents supporting Snowden's claims, including emails he says he sent to the NSA’s compliance office.