WASHINGTON — Nearly two years after he admitted lying to federal investigators about his contacts with a Russian ambassador, a lawyer for former national security adviser Michael Flynn accused the government Tuesday of covering up documents that she claims would have exonerated him.

What those documents are — and whether they, in fact, exonerate Flynn — is still up for debate.

Sidney Powell, a combative conservative lawyer and frequent Fox News commentator, accused prosecutors of withholding evidence that would help prove Flynn's innocence. She also accused federal officials, including former leaders of the FBI, of a longstanding effort to frame President Donald Trump's former national security adviser and called for the entire prosecution team to be removed from the case.

"There is egregious government misconduct and longtime suppression of Brady material that should’ve been provided to defense before there ever was a plea," Powell said during a hearing Tuesday, referring to a rule that requires the government to turn over evidence that could prove a defendant's innocence.

U.S. District Judge Emmet Sullivan did not seem receptive, asking Powell if the evidence she's accused the government of suppressing is materially — and not just theoretically — relevant. He also pressed Powell on what she meant by exonerating Flynn and whether the plea deal will be withdrawn.

"To show what, that he's innocent of this charge?" Sullivan asked.

"To show that the entire prosecution should be dismissed," Powell said, citing "egregious government misconduct" and bias against Flynn.

The former Army general was among the first in the president's orbit to be charged as part of former special counsel Robert Mueller's investigation into Russian meddling in the 2016 election. His sentencing in Washington has been delayed for nearly a year to allow him to finish his cooperation with prosecutors. Though both parties agree that that cooperation is over, they have been at a deadlock on how to proceed.

Assistant U.S. Attorney Brandon Van Grack pushed for a sentencing date later this year and left open the possibility that prosecutors will seek prison time. Powell said "there is far more at stake here than sentencing," alleging that evidence, including memos and portions of infamous text messages between former FBI officials Peter Strzok and Lisa Page, have been withheld and would've exonerated Flynn from allegations that he's a Russian agent.

Van Grack said Flynn was never accused of being an agent of Russia, and the charge he pleaded guilty to was lying to federal investigators. He also said Flynn was well aware of the Strzok and Page text messages, including the ones that were not available to the public, before he pleaded guilty.

Flynn's cooperation with prosecutors involved testifying against his former business associate who was accused of secretly lobbying on behalf of the Turkish government. But prosecutors called into question Flynn's cooperation shortly before he was supposed to testify at the July trial of his former business partner in federal court in Alexandria, Virginia.

Days before Bijan Rafiekian's trial was supposed to begin, prosecutors said they will not call Flynn to the stand and, instead, labeled their former star witness a "co-conspirator" in the case. Flynn's defense team pushed back against the "co-conspirator" designation, calling the government's new position about Flynn's status "disingenuous" and was not based on any new evidence, according to court filings. Defense attorneys also claimed that the government's sudden "about-face" could be a "retaliation" because prosecutors were not satisfied with his testimony.

"While Mr. Flynn does not dispute the government's right to decide how to present its case and which witnesses to call, the government's sudden decision to reverse its long-stated position that Mr. Flynn is its cooperation witness, and to turn him into an unindicted coconspirator, is extremely prejudicial to Mr. Flynn," his defense attorneys said in a court filing.

They also said that prosecutors' reversal in the Virginia case "does not diminish" Flynn's cooperation and should not impact any sentence Flynn receives in his own case in Washington. Prosecutors in Washington said last month that they will reassess their position on Flynn's sentence after Rafiekian's trial.

Flynn had been widely known to have been under scrutiny over his contacts with Russia and his firm's business dealings with a Dutch company with ties to the Turkish government. He did not initially register as a foreign agent, a requirement under the Foreign Agents Registration Act, or FARA, and did so only belatedly amid news reports about his dealings with foreign governments. Mueller's team did not charge him for failing to register.

Instead, Flynn pleaded guilty in 2017 to lying to the FBI about his contacts with former Russian ambassador Sergey Kislyak during the presidential transition. Flynn, however, admitted making "materially false statements and omissions" in documents he filed with the Justice Department's FARA unit about his company's dealings with the Turkish government.

Mueller's office had initially recommended that Flynn be sentenced to probation because he had provided "substantial assistance" to their investigation, including giving them insight into links between Russia and Trump's campaign.

Flynn's sentencing fell apart during a hearing last December, when Sullivan delivered a blistering rebuke of the three-star general.

"Arguably, you sold your country out," Sullivan told Flynn, later agreeing to delay the sentencing.

Brad Heath, Kevin Johnson and Bart Jansen contributed to this article.