WASHINGTON — The Justice Department dropped its criminal case on Thursday against Michael T. Flynn, President Trump’s first national security adviser, who had previously pleaded guilty to lying to F.B.I. agents about his conversations with a Russian diplomat.
The extraordinary move comes amid a sustained attack by Mr. Flynn’s lawyers on prosecutors and the F.B.I., accusing them of egregious conduct. In recent days, Mr. Flynn’s lawyers said the Justice Department had uncovered new documents that pointed to misconduct, particularly in investigators’ interview of Mr. Flynn in January 2017 as part of its inquiry into whether Trump advisers conspired with Russia’s election interference.
Law enforcement officials cited that interview in moving to drop the charges, saying in a court filing that the some of newfound documents showed that the questioning “was untethered to, and unjustified by, the F.B.I.’s counterintelligence investigation into Mr. Flynn” and that the case did not meet the legal standard that Mr. Flynn’s lies be “materially” relevant to the matter under investigation.
In a possible sign of disagreement with the Justice Department decision, Brandon L. Van Grack, the department lawyer who led the prosecution of Mr. Flynn, abruptly withdrew from the case on Thursday. Mr. Flynn’s lawyers have repeatedly attacked Mr. Van Grack by name in court filings, citing his “incredible malfeasance.”
Responding to the news, Mr. Trump told reporters that Mr. Flynn was “an innocent man,” and said he now views him as an “even greater warrior.”
Mr. Flynn first pleaded guilty in late 2017 to lying to investigators and cooperated extensively before moving to withdraw his plea and fight the case in court. He had also entered a guilty plea a second time in 2018 at an aborted sentencing hearing.
And in a highly unusual step, Attorney General William P. Barr assigned an outside prosecutor to review the Justice Department’s case. As part of that review, prosecutors turned over documents starting last month that Mr. Flynn’s lawyers said proved the former general had been framed by the F.B.I.
Mr. Flynn’s case grew out of an investigation by law enforcement officials who had reason to suspect that he constituted a national security threat. They learned that he had lied in January 2017 to other White House officials about conversations during the presidential transition with the Russian ambassador to the United States, and they warned the White House that Russia could have blackmailed Mr. Flynn, then the Trump administration’s highest-ranking national security official.
The White House was prepared for the possibility of Mr. Trump pardoning Mr. Flynn last week, according to two people familiar with the discussions. But some advisers urged him to hold off and let the case play out, either with the Justice Department or with the judge in the case, according to the people familiar with the discussions.
So Mr. Trump agreed, and he held off. If he was briefed by Mr. Barr long before the decision, he did not let on to advisers, according to those familiar with the discussions.
After more than a year of cooperating with investigators, Mr. Flynn adopted a more combative stance last year when he hired new lawyers who have accused Mr. Van Grack and other prosecutors in a blizzard of court filings of “bad faith,” pressuring their client to cooperate and withholding exculpatory evidence.
But the federal judge in Washington overseeing the case, Emmet G. Sullivan, forcefully rejected most of the defense’s claims in a 92-page ruling in December.
Mr. Flynn, a decorated lieutenant general and former head of the Defense Intelligence Agency, was an early supporter of Mr. Trump’s campaign, joining the crowd in a “lock her up” chant about Hillary Clinton at the Republican National Convention in 2016.
Mr. Flynn pleaded guilty in December 2017 to lying to the F.B.I. about his conversations during the presidential transition with the Russian ambassador to the United States at the time, Sergey I. Kislyak.
The F.B.I. had interviewed Mr. Flynn four days after Mr. Trump’s inauguration. Less than a month later, Mr. Flynn was forced to resign as national security adviser. According to the White House at the time, the reason Mr. Flynn was forced to resign was because he was not forthcoming with Vice President Mike Pence about his conversations with Mr. Kislyak.
Mr. Flynn eventually admitted that those discussions were part of a coordinated effort by the president’s aides to make foreign policy before they were in power, which undermined the policy of President Barack Obama.
Mr. Flynn also lied in federal filings about his lobbying work for the Turkish government, court papers show. Two of his former business associates were charged with conspiring to violate federal lobbying rules in cases related to the special counsel inquiry.
Mr. Trump raised concerns about the F.B.I.’s scrutiny of Mr. Flynn during the early days of his presidency, asking the F.B.I. director at the time, James B. Comey, to end any investigation into Mr. Flynn. Details about the president’s request became public a few months later after Mr. Trump fired Mr. Comey and helped prompt Mr. Mueller’s appointment as special counsel.
After firing Mr. Flynn, the president thought he had put an end to the Russia inquiry that had been dogging him for months.
“Flynn met with the Russians. That was the problem. I fired Flynn. It’s over,” Mr. Trump said, according to a book published by former Gov. Chris Christie of New Jersey, an ally of the president’s.
The special counsel’s prosecutors considered Mr. Flynn a key early cooperator as “one of the few people with long-term and firsthand insight” into their inquiry into whether any Trump associates criminally conspired with Russia’s 2016 election interference.
Maggie Haberman contributed reporting from New York.