Two high-level court maneuvers are expected to reveal new details of his investigation on Friday, which will make life even more unpleasant for President Donald Trump and his inner circle.
Mueller has a deadline Explain to a judge in Washington why he has already sentenced Trumps and accused detained former campaign manager Paul Manafort of having lied and broken a cooperation agreement.
And he also has to submit documents to a New York court recommending whether Trump's former personal court recommends lawyer Michael Cohen should go to jail and for how long after Cohen had turned against his former top client and agreed with the special advocate.
Prior to what might turn out to be a crucial day in the investigation, Trump beat out at Mueller's team.
"Is that really America? Witch Hunt!" Trump tweeted after quoting a Fox News host who had criticized the investigation.
It has become clear in recent weeks, however, that the Special Lawyer liaises with key witnesses and former Trump employees with procedures and files to suggest a pattern of questionable behavior by the President.
Since then, Mueller has built a tapestry of disclosures that began with the settlement of a hacking operation by the Moscow intelligence agencies and revealed several connections between Russians and people near Trump – and repeated lies about these contacts.
Friday The activity will end an ominous week for Trump, in which it has become clear that the investigation below the surface is much broader than is publicly apparent. It can now be said that Müller digs for possible clashes with the Russians, obstructs the judiciary, establishes contacts with Russian officials during the Trump transition, possible campaign finance violations, and the business secrets of the president.
"It's not about Russian collusion, it's about parsing words," Stone said. "It's about trial crimes and perjury traps, and I decline to participate."
"Crimes and Lies"
The details of Mueller's team are closely monitored to see if Manafort runs the risk of spending the money his entire life in prison, lied about activities that could affect Trump or high-ranking election officials, or solely on business Interests in Ukraine, which have led to the victimization of fraud or other issues.
The lawyers at Manafort denied their clients that they had lied and had the opportunity to challenge the claims of the solicitor before his March 5 ruling.  It is possible that some of Müller's explanations, as in the Flynn file, are black. However, a spokesman for the Special Representative's Office said that at least some of the files will be public.
Ross Garber, a lawyer specializing in impeachment, said on CNN's "New Day" Thursday that cooperation was not normal agreement to collapse this way, given the intense negotiations that normally take place before.
"It'll be interesting to see if something new came up that nobody expected, but it's very unusual," said Garber.
Mueller's decision to speak toughly against Manafort but to grant leniency to Flynn has been widely interpreted as a sign that he will reward those involved in the investigation who are willing to tell the truth about what happened do not tolerate disability.
Cohen resets the "compass" of his life
Cohen has sentenced the court to imprisonment after he admitted tax fraud and had lied to Congress about Trump's business aspirations in Moscow to the president to obtain. & # 39; In his political narrative, he has no relations with Russia.
Cohen's lawyers said in a memo that her client, turning to Trump, for whom he once said he wanted to take a bullet, decided to "change his mind" internal compass heading north a productive, ethical and consistently law-abiding life.
Convicted documents filed by both sides in the case have linked important points in the investigation.
In fact, the project was alive until June 2016, as a statement received at the Mueller court had said several times with Trump
The revelations were important because Trump had insisted throughout the campaign that he had no business ties with Russia.
The President was a long-time campaigner to Russia and formulated his Supplement Statements about President Vladimir Putin to promote his own financial interests
Cohen also pleaded guilty to protesting financial litigation in connection with women's hush-money alleged affairs with Trump, which the president denied.
"Michael kept his client up-to-date and acted on his client's instructions." Cohen's lawyers wrote in their conviction record.
"Michael felt obliged to support client-1 (Trump) on Client-1's instructions to prevent Woman-1 and Woman-2 from spreading stories that adversely affect the campaign and client -1 and his family would cause a personal embarrassment. "
Cohen, who met 63 months in prison under his original lawsuit with New York prosecutors, hopes that Müller will grant him the same treatment as Flynn. The Special Lawyer said this week in court that the former National Security Advisor should not receive a jail sentence following the investigation by Flynn. However, editorial staff in accompanying documents made it impossible to assess what this collaboration entailed and whether the president was in danger.
Trump has responded angrily to the idea that Cohen Mueller might get cooperation in return.
"He lied about this result and I think he should serve a full and complete prison sentence," the president tweeted earlier this week.
Depending on the details Mueller unveils on Friday, it is almost certain Trump's allies will resort to their familiar argument that the special lawyer has still not proven cooperation between Russia and the campaign – the original mandate of the probe.
But with every move he makes, Mueller seems to be getting closer to people closest to the president himself, so in the broadest sense there's every chance that Friday could be another tough day for Trump in court.
Sara Murray and Katelyn Polantz of CNN have contributed to this story.