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(CNN) —  

President Donald Trump’s first national security adviser, Michael Flynn, has fired his lawyers who arranged a 2017 plea deal that helped set the tone for others to cooperate with special counsel Robert Mueller’s investigation.

Flynn’s attorneys, Rob Kelner and Steve Anthony, said in a court filing Thursday morning their longtime client was “terminating” them, and that he has already found new legal representation.

The new lawyer or lawyers have not yet announced who they are to the court.

The announcement also comes shortly after a transcript was released of a voicemail Kelner had received from Trump personal attorney John Dowd on the eve of Flynn’s plea deal, suggesting the White House should be kept apprised of what Flynn was doing. Flynn turned that voicemail over to prosecutors – and Mueller credited him for doing so. The voice mail became part of Mueller’s investigation into whether Trump had tried to sway cooperators.

Flynn, who continues to delay his sentencing after a disastrous court hearing last December and subsequent developments that put the spotlight on the Covington & Burling law firm, was one of the Mueller’s investigations earliest and important cooperators.

Flynn admitted in December 2017 to lying to the FBI while they interviewed him in the White House in January 2017 about discussing foreign policy with then-Russian ambassador Sergey Kislyak and about his lobbying for Turkey.

Once he agreed to help Mueller, the fired Trump adviser sat for 19 interviews with the special counsel’s office and other federal prosecutors.

Yet at the December 2018 hearing, Judge Emmet Sullivan grew angry about an implication in a court filing by Flynn’s attorneys that his lies were not as serious or deliberate as other Mueller defendants.

The lawyers took full responsibility for making the argument before the judge.

“The decisions,” Kelner said at the December hearing, “made by me, made by Mr. Anthony, are entirely ours and really should not and do not diminish in any way General Flynn’s acceptance of responsibility in this case.”

Kelner and Anthony declined to comment Thursday.

The lawyers from Covington, a large and storied Washington law firm, have had a highly visible and fraught role in helping to defend Flynn during the Mueller investigation.

Some of their work for Flynn even became significant evidence in Mueller’s investigation of whether the President obstructed justice.

Prosecutors released the full transcript of the Dowd voicemail last week following a court order from Sullivan, and it was quoted in the Mueller report.

The Covington attorneys helped to win the most lenient support from prosecutors for Flynn compared to any cooperator in the Mueller investigation. Mueller’s team asked the judge to give Flynn as little as no jail time.

Mueller also interviewed the Flynn attorney as a witness in the investigation, an unusual step – and cited those conversations in his report.

After delaying Flynn’s sentencing last year, Flynn and his attorneys have become central to another criminal case against his former lobbying partner Bijan Rafiekian, who also goes by Bijan Kian. Rafiekian has pleaded not guilty, and Flynn is expected to testify against him at that trial this summer.

The Covington lawyers, too, have been roped into that case. Previously, Rafiekian won access to legal work the law firm did for the Flynn Intel Group.

A judge continues to consider whether Covington passed along fraudulent information to the Justice Department when they handled foreign lobbying disclosures for Flynn’s former company. Prosecutors said that in that situation, that they believe the law firm hadn’t realized the statements they made to the Justice Department were false.

Taken together, it’s possible that Covington’s legal work for Flynn – and Flynn’s own crime of lying to the FBI, pleading guilty and cooperating with Mueller – could be put on full display at the upcoming trial.

Flynn’s sentencing in DC federal court has not yet been rescheduled.