Attorneys for former national security adviser Michael T. Flynn claimed Friday that the Justice Department has turned over “stunning” evidence under seal from an external review of special counsel Robert S. Mueller III’s prosecution that shows that their client was “set up and framed” by the FBI.

Flynn’s lawyers did not provide specifics, and the material turned over remains subject to a protective order barring public release of evidence in the case. But they urged a judge to consider it as part of their request to withdraw Flynn’s guilty plea to lying to the FBI during its investigation of Russian interference in the 2016 election. Flynn still awaits sentencing.

The new material “proves Mr. Flynn’s allegations of having been deliberately set up and framed by corrupt agents at the top of the FBI,” Flynn attorneys Sidney Powell and Jesse Binnall wrote in a three-page filing.

“The government has deliberately suppressed this evidence from the inception of this prosecution — knowing there was no crime by Mr. Flynn,” Powell and Binnall wrote.

Attorneys for Flynn have made similar claims several times since he switched defense teams last June, but this was the first allegation that surfaced from an external review personally ordered this winter by Attorney General William P. Barr. In late January or early February, Barr directed the U.S. attorney for eastern Missouri, Jeffrey B. Jensen, to review and “assist” federal prosecutors in Washington, D.C. The U.S. attorney’s office in the District began handling Flynn’s case after Mueller’s office closed in March 2019.

The status reports Friday deepened the mystery around Flynn’s case and seemed likely to fuel political recriminations surrounding the matter. Supporters of Flynn and President Trump have attacked Mueller’s probe as a “witch hunt,” while others allege that Trump and Barr have been intervening in sensitive cases to help the president’s friends and political allies.

Flynn, 61, was fired from the White House in February 2017. He pleaded guilty that December to lying about discussing potential relief from U.S. sanctions with then-Russian Ambassador Sergey Kislyak before Trump took office, and about his lobbying work for the government of Turkey.

The former three-star Army general was one of the first and highest-ranking Trump aides to be convicted and cooperate in Mueller’s investigation.

However, his case became one of the most bitterly contested after Mueller’s probe ended. Flynn’s new lawyers began moving to void his conviction, alleging that he was the victim of a partisan conspiracy by prosecutors, U.S. intelligence and national security officials, and even his initial attorneys.

In separate filings Friday, the U.S. attorney’s office for the District of Columbia disclosed to the court that it has turned over to Flynn an unspecified number of documents “obtained and analyzed” by Jensen’s office in the past two months in an “ongoing review,” adding that “additional documents may be forthcoming.”

The outside review has “involved the analysis of reports related to the investigation” and “communication and notes” by associated FBI personnel, according to the notice, which was filed by the office of interim U.S. attorney Timothy J. Shea of the District of Columbia, Barr’s former counsel.

The filings from Shea’s office also said prosecutors had turned over more than 100 pages of signed declarations and 500-plus pages of exhibits from the law firm Covington & Burling — which initially defended Flynn — in response to Flynn’s charges that it misled him and allowed him to plead guilty to cover up its own errors.

U.S. District Judge Emmet G. Sullivan gave prosecutors until May 8 to review the declarations, determine whether to interview Covington personnel, and decide when and how it would respond to Flynn’s allegations.

Flynn in January moved to take back his plea. He claimed that he was in fact innocent and a victim of ineffective defense counsel as well as unscrupulous prosecutors who demanded his false testimony against his former business partner.

Prosecutors gave shifting recommendations for Flynn’s punishment over the winter, even as the top U.S. prosecutor’s office for the District of Columbia underwent a dramatic shake-up.

In late January, as Barr tapped Shea to take over and dispatched Jensen to review Flynn’s case, prosecutors without explanation backed off their earlier suggestion that up to six months in prison was appropriate for Flynn.

Prosecutors reemphasized that, per his plea agreement, probation remained a “reasonable sentence” that they would not oppose.

Separately, in February, Justice Department leadership retreated from line prosecutors’ sentencing recommendation for Trump’s longtime political confidant Roger Stone, prompting all four prosecutors in the Washington office to quit the case.