The filing by special counsel Robert Mueller provides the first details of Flynn's assistance in the Russia investigation, including that he participated in 19 interviews with prosecutors and cooperated extensively in a separate and undisclosed criminal probe. But the filing's lengthy redactions also underscore how much Mueller has yet to reveal.
It was filed Tuesday, two weeks ahead of Flynn's sentencing and just over a year after he became one of five Trump associates to plead guilty in the Russia probe, in his case admitting to lying to the FBI about conversations with the Russian ambassador to the U.S.
Though prosecutors withheld specific details of Flynn's cooperation because of ongoing investigations, their filing nonetheless illustrates the breadth of information Mueller has obtained from people close to Trump as the president increasingly vents his anger at the probe — and those who cooperate with it.
This week, Trump accused his former lawyer, Michael Cohen, of making up "stories" to get a reduced prison sentence after pleading guilty to lying to Congress and also praised longtime confidante Roger Stone for saying he wouldn't testify against Trump.
It's unclear if Trump will now turn his fury on Flynn, whom Trump bonded with during the 2016 campaign.
Trump has repeatedly lamented how Flynn's life has been destroyed by the special counsel's probe. At one point, he tried to protect Flynn by asking former FBI Director James Comey to drop an investigation into his alleged false statements, according to a memo Comey wrote after the February 2017 encounter.
That episode, which Trump has denied, is among those under scrutiny by Mueller as he probes whether the president attempted to obstruct the Russia investigation.
Federal sentencing guidelines recommend between zero and six months in prison, and Mueller's office said Flynn's cooperation merits no prison time.
Prosecutors said Flynn's early cooperation was "particularly valuable" because he was "one of the few people with long-term and firsthand insight" into the events under investigation. They noted his cooperation likely inspired other crucial witnesses to cooperate.
Mueller's team credited Flynn with serving 33 years in the U.S. Army, including five years in combat. But prosecutors also said the long military and government service that sets him apart from all other defendants in the investigation made his deception more troublesome.
"The defendant's extensive government service should have made him particularly aware of the harm caused by providing false information to the government, as well as the rules governing work performed on behalf of a foreign government," they wrote.
Flynn's case has stood apart from those of other Trump associates, who have aggressively criticized the investigation, sought to undermine it and, in some cases, been accused of lying even after agreeing to cooperate.
Trump's former campaign chairman, Paul Manafort, is accused of repeatedly lying to investigators since his guilty plea. Another Trump campaign aide, George Papadopoulos, is serving a 14-day prison sentence and, though he pleaded guilty to the same crime as Flynn, was denied probation because prosecutors said his cooperation was lacking.
But Flynn has largely remained out of the public eye, appearing only sporadically in media interviews or campaign events, and avoided criticizing the Mueller probe despite widespread encouragement from his supporters to go on the offensive. He has instead spent considerable time with his family and worked to position himself for a post-conviction career.
Another highly anticipated filing is expected Friday from Mueller's office, detailing the lies that prosecutors say Manafort told them after his guilty plea.
In Tuesday's filing, prosecutors emphasized that the conduct Flynn lied about cuts to the core of the investigation into any coordination between the Trump campaign and the Kremlin.
Flynn's false statements stemmed from a Jan. 24, 2017, interview with the FBI about his interactions with Sergey Kislyak, Russia's then-ambassador to the U.S., as the Obama administration was levying sanctions on the Kremlin in response to election interference.
Mueller's office blamed Flynn for other senior Trump transition officials making misleading public statements about his contacts with Russia, an assertion that matches the White House's explanation of Flynn's firing.
"Several senior members of the transition team publicly repeated false information conveyed to them by the defendant about communications between him and the Russian ambassador regarding the sanctions," the filing said.
As part of his plea deal, Flynn said members of Trump's inner circle, including his son-in-law and White House aide Jared Kushner, were involved in — and at times directing — his actions in the weeks before Trump took office.
According to court papers, in mid-December 2016, Kushner directed Flynn to reach out to several countries, including Russia, about a U.N. Security Council resolution regarding Israeli settlements. During those conversations with Kislyak, Flynn asked Russia to delay or vote against the resolution, a request the Kremlin ultimately rejected.
Flynn also admitted that later in December 2016 he asked Kislyak not to retaliate in response to the Obama administration sanctions, something he initially told FBI agents he didn't do. Flynn made the request after discussing it with deputy national security adviser K.T. McFarland, who was at Trump's Mar-a-Lago resort, and being told that Trump's transition team did not want Russia to escalate the situation.
Flynn was forced to resign his post on Feb. 13, 2017, after news reports revealed that Obama administration officials had warned the Trump White House about Flynn's false statements. The White House has said Flynn misled officials— including Vice President Mike Pence — about the content of his conversations.
Flynn also admitted to making false statements about unregistered foreign agent work he performed for the benefit of the Turkish government, a matter Mueller's team cited in Tuesday's filing. Flynn was under investigation by the Justice Department for the work when he became national security adviser.