Mueller is about to drop major new details about 3 of the most important players in the Russia probe

The special counsel Robert Mueller's office has told defense lawyers in recent weeks that it is "tying up loose ends" in the ongoing investigation into Russia's interference in the 2016 election and whether members of President Donald Trump's campaign colluded with Moscow, Yahoo News reported.

The news is not entirely unexpected. Last month, CNN reported that the special counsel had begun drafting his final report in the Russia investigation.

And this week, prosecutors are set to file several court documents that could reveal major new details about three key players in the Russia investigation: former national security adviser Michael Flynn, former Trump campaign chairman Paul Manafort, and former Trump lawyer Michael Cohen.

All three men have pleaded guilty and have been cooperating with prosecutors.

Flynn has been working with Mueller's team since last December, after he pleaded guilty to lying to the FBI.

In August, Cohen pleaded guilty as part of a separate Manhattan US attorney's office investigation, and he has since given over 70 hours of voluntary interviews to the special counsel. He also pleaded guilty in the Mueller investigation to one count of lying to Congress last week and his lawyers say he expects to cooperate further.

Manafort, meanwhile, pleaded guilty to conspiracy and obstruction in September and struck a plea deal with prosecutors to answer any and all questions they had about the Russia investigation and any other federal criminal inquiries.

But prosecutors revealed last month that Manafort had breached his plea deal by allegedly lying to investigators and committing additional crimes since agreeing to cooperate.

Prosecutors were also reportedly furious when they learned that Manafort's team was briefing Trump's lawyers on everything he was being asked about after he agreed to cooperate.

DOJ veterans told INSIDER that they had never heard of a cooperator maintaining contact with the potential target of an investigation after striking a deal with prosecutors, and that such communications could tank a cooperation agreement.

Mueller's team is slated to submit a brief to the court on Friday about its claim that Manafort violated his plea agreement. The special counsel's office told Yahoo News that the Manafort memo "will be public," although some parts of it may be redacted or submitted under seal to protect the investigation.

But for the most part, prosecutors will spell out in detail the matters the former Trump campaign chairman misled them about, and their public disclosures could shed new light on where the Russia investigation stands.

The national-security experts at Lawfare wrote, moreover, that the public may also learn more "in the context of that briefing about the relationship Manafort appears to have maintained, through counsel, with the White House after his plea and cooperation agreement."

Cohen's lawyers, meanwhile, submitted a sentencing memo on his behalf last week that contained a slew of bombshells about Trump and his interactions with Cohen last year and before the 2016 election.

Among other things, his lawyers said that when Cohen was breaking campaign finance laws at Trump's direction before the election, Cohen was also keeping Trump "contemporaneously informed" of his actions.

They also said Cohen was "in close and regular contact" with Trump's lawyers and White House staffers while he was drafting false testimony to give to Congress last year about his involvement in the Trump Organization's effort to build a Trump Tower in Moscow during the election.

Cohen's sentencing is scheduled for December 12, and prosecutors are set to submit their own sentencing memo in his case on Friday. Lawfare said it will be important to "see how they characterize Cohen's cooperation and to what extent they also urge leniency and on what points — if any — they dispute the picture of Cohen's cooperation that Cohen's lawyers have painted."

Flynn's sentencing hearing is scheduled for December 18, and prosecutors are slated to submit a sentencing memo for him on Tuesday.

It's unclear how much of it will be redacted, but because the nature of his cooperation has been shrouded in mystery since last year, it's likely that any new details that come out of the filing will help inform the public about where the Russia investigation is headed.