Federal prosecutors on Tuesday challenged former national security adviser Michael Flynn's claim that the U.S. Justice Department has withheld exculpatory evidence from him, arguing that his defense lawyers were advancing unfounded "conspiracy theories" in the hope of upending his guilty plea.

In a 22-page court filing, prosecutors urged a federal judge in Washing to reject Flynn's request for evidence he believes was improperly hidden from him, saying the demand from his new defense lawyers amounted to a "fishing expedition." Prosecutors also pointed to statements Flynn made last year in which he denied having any concerns about whether the Justice Department had met its obligation to turn over potentially exculpatory evidence, known as Brady material.

"The defendant's motion is not a search for Brady material. It is a fishing expedition in hopes of advancing conspiracy theories related to the U.S. government's investigation into Russian interference in the 2016 presidential election," prosecutor Brandon Van Grack said in Tuesday's court filing. "The government has already provided any evidence that could reasonably be construed as favorable and material for the defendant at sentencing."

Flynn pleaded guilty in 2017 to lying to federal investigators about communications he had with Sergey Kislyak, the longtime Russian ambassador to the United States, during the Trump presidential transition. As part of his plea deal, Flynn cooperated with Special Counsel Robert Mueller III's team as it probed Russian interference in the 2016 election and spoke with federal investigators in a case against his former business partner, Bijan Kian.

In December 2018, with prosecutors backing his request for leniency, Flynn appeared before U.S. District Judge Emmet Sullivan of the District of Columbia for sentencing. But when Sullivan signaled he would hand down a sentence with prison time, Flynn, then represented by lawyers from Covington & Burling, asked to delay the proceeding until he testified against Kian.

Flynn fired his Covington team in June and has since adopted an aggressive stance toward prosecutors. He hired Sidney Powell, a Dallas defense lawyer widely known for her criticism of the Mueller probe. Ahead of Kian's trial, prosecutors decided not to call Flynn to testify because he changed his account of their work for Turkish interests. A jury in Alexandria found Kian guilty of secretly lobbying on behalf of Turkey, but a federal judge threw out the conviction last week, ruling that the evidence had been insufficient.

Powell has accused the government of "egregious" misconduct in Flynn's case. But she has not filed papers seeking to withdraw Flynn's guilty plea.

Powell, working with defense lawyers at the Alexandria, Virginia, firm Harvey & Binnall and at the William Hodes Law Firm, contend that prosecutors put "excruciating pressure" on Flynn to plead guilty.

"They continued to hide that exculpatory information for months—in direct contravention of this court's order—and they continue to suppress exculpatory information to this day," Flynn's defense lawyers said in August.

In their filing Tuesday, prosecutors said the request for additional evidence was intended not to obtain facts but to have the case dismissed.

"Confirming that the defendant and his new counsel are in search of a result, not the facts, defense counsel was recently interviewed on television and exclaimed, 'I'm expecting, frankly, that we find evidence that warrants dismissal of the case for egregious government misconduct,'" prosecutors wrote, quoting a statement Powell made during an appearance on Fox Business.

Prosecutors said Powell's arguments were "premised on conspiracy theories" and that her most frequent target was the special counsel's office.

"For example, the defendant and his counsel allege that the Special Counsel's Office manipulated or controlled the press. The claim is divorced from facts and reality," prosecutors said in their new filing.

Emmet Sullivan U.S. District Judge Emmet Sullivan of the District of Columbia. Photo: Diego M. Radzinschi/AML

Sullivan has set a Nov. 5 hearing where prosecutors and defense lawyers will argue over whether any favorable evidence was concealed. The judge set a tentative sentencing date for Dec. 18.

At a hearing last month, Van Grack suggested the Justice Department might drop its past support for leniency and ask Sullivan to sentence Flynn to prison. In a footnote in Tuesday's filing, Van Grack wrote that Powell's statements have raised questions about whether Flynn has lived up to the terms of his plea deal.

"Based on filings and assertions made by the defendant's new counsel, the government anticipates that the defendant's cooperation and candor with the government will be contested issues for the court to consider at sentencing."