Special Counsel Robert Mueller filed a memorandum Tuesday recommending a lenient sentence -- with the possibility of no prison time -- for convicted former national security adviser Michael Flynn, and stating that Flynn has offered "substantial" help to investigators about "several ongoing investigations."

The bombshell release comes as additional sentencing memorandums are expected within days in the cases of former Trump attorney Michael Cohen and ex-campaign chairman Paul Manafort, amid multiple reports and indications that the long-running Mueller probe into ties between President Trump's team and Russia is winding down.

“Given the defendant’s substantial assistance and other considerations set forth below, a sentence at the low end of the guideline range, including a sentence that does not impose a term of incarceration – is appropriate and warranted," the memo states.

Flynn sat for 19 interviews with the Special Counsel's office and other Department of Justice attorneys, according to the sentencing memorandum and a heavily redacted supplemental filing attached to the end of the primary memorandum.

Responding to the documents' release, Trump attorney Rudy Giuliani told Fox News that Mueller was "spitting on the sidewalk, with major repercussions for many.”

He added that there was nothing in the sentencing memo to suggest collusion between the Trump team and Russia, and denounced the Mueller team as “overzealous media inspired prosecutors" and "sick puppies.”

The new documents do not provide specifics about what exactly Mueller has learned from Flynn, but they indicate he provided "documents and communications" about his time working with the Trump administration during the presidential transition period.

Mueller's addendum to the memorandum states that Flynn has "assisted with several ongoing investigations," including the Russia probe and an apparently separate "criminal investigation."

"Additionally, the defendant's decision to plead guilty and cooperate likely affected the decisions of related firsthand witnesses to be forthcoming with the [Special Counsel] and cooperate," prosecutors added.

Further information about the criminal investigation, including the subject of that probe, is redacted. The document also suggests Flynn helped with a third ongoing investigation, but details on that probe are redacted in their entirety. It was not clear if Mueller is handling those investigations.

"The defendant provided firsthand information about the content and context of interactions between the transition team and Russian government officials," the addendum reads. "For example, after the election, the defendant communicated with the Russian ambassador to the United States as a representative of the transition team on two sensitive matters: a United Nations Security Council vote on a resolution calling for Israel to cease settlement activities in Palestinian territory and the Obama Administration’s imposition of sanctions and other measures on Russia for interfering in the 2016 election."

It continues: "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."

Supplemental Sentencing Memo by Fox News on Scribd

The memo goes on to praise Flynn's military career and his decision to "accept[] responsibility in a timely fashion."

"[D]efendant’s military and public service are exemplary," the memo stated. "He served in the military for over 33 years, including five years of combat duty, led the Defense Intelligence Agency, and retired as a 3-star Lieutenant General."

Although Flynn's "early cooperation was particularly valuable because he was one of the few people with long-term and firsthand insight regarding events and issues under investigation," Mueller's team made clear they thought he should have known better.

"[S]enior government leaders should be held to the highest standards," the filing concludes.

Yahoo News reported Monday that Mueller has indicated his sweeping probe is now simply "tying up loose ends" as it nears its conclusion.

"[S]enior government leaders should be held to the highest standards."
— Special Counsel Robert Mueller

Flynn pleaded guilty in December 2017 to making false statements to the FBI with regard to his communications with Russian Ambassador Sergey Kislyak. In late 2016, the two allegedly spoke about the U.S. sanctions imposed on Russia.

Flynn was fired from the White House on Feb. 13, 2017, after he misled Trump administration officials, including Vice President Pence, on his communications.

Flynn also admitted to making false statements about his work as an unregistered foreign agent to benefit the Turkish government. Flynn was under investigation by the Justice Department for that work when he became national security adviser.

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But the special counsel’s team has delayed Flynn’s sentencing date for over a year, repeatedly saying that “due to the status” of the investigation, “the parties do not believe that this matter is ready to be scheduled for a sentencing hearing at this time.”

Questions also have been raised about the Flynn plea itself, considering a congressional Republican report earlier this year claimed fired FBI boss James Comey once testified that FBI agents did not think Flynn intentionally lied.

Former Trump national security adviser Michael Flynn leaves federal court in Washington, Dec. 1, 2017. (Associated Press)

As part of Flynn’s plea deal, he agreed to cooperate with Mueller’s office on “any and all matters” deemed relevant. The plea deal said Flynn’s cooperation may include answering questions, taking government-administered polygraph examinations, providing sworn statements and participating in “covert law enforcement activities.”

Mueller’s team has entered plea agreements with several Trump associates, including former Trump campaign chairman Paul Manafort, who the special counsel now alleges breached their plea deal by lying to investigators. Manafort was convicted on multiple counts of financial fraud over the summer in connection with work he completed in Ukraine as a political consultant.

Mueller’s team also entered a deal last week with former longtime Trump personal attorney Michael Cohen, after he pleaded guilty to making false statements to Congress regarding his description of the Trump Organization’s plans to build a Trump Tower in Moscow. Cohen told the Senate Intelligence Committee that discussions about the project with Russia ended in January 2016, prior to the Iowa caucuses, the first contest in the presidential primaries.

Cohen admitted in court last week that discussions about the Moscow Project did not end until June 2016, well after the presidential race got underway.

The Mueller-Cohen deal also involves cooperation with federal prosecutors. A sentencing memorandum is expected to be filed in Cohen's case on Friday.

Other than Flynn and Cohen, Mueller’s team charged former Trump campaign foreign policy adviser George Papadopoulos with making false statements to the FBI. He is currently serving a 14-day prison sentence.

Former senior Justice Department official James Trusty told Fox News that the guilty pleas related to making false statements “do[] not suggest a particularly successful investigation.”

“It’s heavy on false statements charges, and that doesn’t suggest that it’s moving in the right direction for the prosecution,” Trusty said. “It doesn’t suggest to me that they’re making a lot of headway on the substance of their investigation which is Russian collusion.”

He added: “As an ex-prosecutor, false statements are a very distant second place.”

But according to memos penned by Comey, President Trump tried to protect Flynn by asking Comey to let the investigation into his false statements go. Trump has denied asking Comey to drop the investigation, but that conversation between the fired FBI director and the president is reportedly one under scrutiny by the special counsel’s office as he investigates whether Trump attempted to obstruct the Russia investigation.

But Trusty said that during the FBI’s investigation of Hillary Clinton’s private email server, investigators and Comey “swore off even pursuing false statements charges,” quoting a recent Justice Department inspector general report.

“Are there two sets of rules?” Trusty said. “It’s a fair question that someone in the FBI or Justice Department ought to answer at some point.”

Fox News' John Roberts, Brooke Singman, and The Associated Press contributed to this report.