Prosecutors said that his cooperation has been substantial.
The filing provided the first details of Flynn's assistance in the Russia investigation. Prosecutors say that he participated in 19 interviews and cooperated extensively in a separate and undisclosed criminal probe.
The filing comes 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 US.
The most interesting about the Flynn filing is a heavily redacted addendum that added more tantalizing hints. It indicated that Flynn was also aiding one or more other federal criminal investigations related to the Trump campaign, but not being led by Mueller.
And the filing's lengthy redactions also underscore how much Mueller has yet to reveal.
Flynn was forced to resign his post on February 13, 2017, after news reports revealed that Obama administration officials had warned the Trump White House about Flynn's false statements.
Trump furiousMeanwhile, President Trump has been increasingly venting his anger at the probe — and those who have cooperated with it.
Read more: Analysis: Despite Flynn's guilty plea, Trump presidency not over yet
This week, Trump accused his former lawyer, Michael Cohen, of making up "stories" to get a reduced prison sentenceafter pleading guilty to lying to Congress.
He also praised longtime confidante and Republican political operative Roger Stone for saying he wouldn't testify against Trump.
Read more: Trump's GOP loyalists like a 'cult of personality,' says ex-governor
Mueller is also investigating a June 2016 meeting that top campaign staff, including chairman Paul Manafort, Trump's son Donald Jr., and son-in-law Jared Kushner, had with a Russian lawyer who had offered dirt on Trump's election opponent Hillary Clinton.
Another highly anticipated filing is due on Friday from Mueller's office. It is expected to give details about the lies that prosecutors say Manafort told them after his guilty plea.
Another Trump campaign aide, George Papadopoulos, has just begun serving a 14-day prison sentence. Although he pleaded guilty to the same crime as Flynn, Papadopoulos was denied probation because prosecutors said his cooperation was lacking.
av/rc (AP, AFP, dpa)
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