Updated

The D.C. Circuit Court of Appeals ruled in an 8-2 decision that D.C. District Court Judge Emmet Sullivan does not have to grant prosecutors' motion to dismiss the criminal case against former national security adviser Michael Flynn.

The en banc review by the full court (minus Judge Gregory Katsas, who recused himself) reverses the decision of a three-judge panel, which had issued a writ of mandamus ordering Sullivan to toss the case. Flynn had argued that Sullivan overstepped his authority by appointing a third-party amicus curiae (friend of the court) to argue against dismissal, even though Flynn and the Justice Department agreed to dispose of the case.

DC CIRCUIT COURT GRILLS LAWYERS IN FLYNN CASE OVER WHETHER CASE SHOULD BE DROPPED

"Quite simply, the only separation-of-powers question we must answer at this juncture is whether the appointment of an amicus and the scheduling of briefing and argument is a clearly, indisputably impermissible intrusion upon Executive authority, because that is all that the District Judge has ordered at this point," the court's opinion said.

"We have no trouble answering that question in the negative, because precedent and experience have recognized the authority of courts to appoint an amicus to assist their decision-making in similar circumstances, including in criminal cases and even when the movant is the government," the opinion continued.

While case dismissals are, by rule, done "leave of court," Flynn's legal team argued that in the vast majority of cases that is a mere formality and this case did not warrant being the rare exception where a judge needed to step in for further review.

In this Dec. 1, 2017, file photo, Michael Flynn, center, arrives at federal court in Washington. (AP Photo/Susan Walsh, File)

In this Dec. 1, 2017, file photo, Michael Flynn, center, arrives at federal court in Washington. (AP Photo/Susan Walsh, File)

Judge Neomi Rao argued in a dissenting opinion that Sullivan is acting improperly because "it is long settled that a district court cannot supervise the prosecutorial decisions of the Executive Branch." In a separate dissent, Judge Karen Henderson stated that Sullivan should have been disqualified from the case because his "conduct patently draws his impartiality into question."

The case will now go back to Sullivan in the District Court, where it is expected he will hear oral arguments from the DOJ -- which has argued in favor of dismissal -- and retired Judge John Gleeson, who was appointed as amicus and already filed a brief opposing dismissal.

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Should Sullivan decide against dismissing the case following arguments, the case would once again move towards sentencing.

Federal prosecutors moved to dismiss Flynn's case — in which he had previously pleaded guilty to providing false statements to the FBI — after FBI records called into question the circumstances surrounding Flynn's interview with investigators. The DOJ was criticized by Democrats for giving Flynn unusual and improperly kind treatment due to his connection to President Trump.

Fox News' Bill Mears contributed to this report.