In the court papers filed Tuesday, Manafort's lawyers claimed that "he attempted to live up to the requirements of his cooperation agreement and provided meaningful cooperation relating to several key areas under current government investigation".
The brief discloses, in passages inexpertly redacted and thus available to the public, that Manafort provided to Konstantin Kilimnik, a business partner in Ukraine with a history with Russian intelligence, poll data from the Trump campaign.
Manafort was among the first Americans charged in Mueller's investigation and has been among the central characters in the case, having led the campaign during the Republican convention and as, U.S. intelligence officials say, Russian Federation was working to sway the election in Trump's favor.
Manafort's lawyers wrote in an improperly redacted portion of the brief that prosecutors said he lied about "sharing polling data with Mr. Kilimnik related to the 2016 presidential campaign".
Manafort, after being convicted of various bank and tax fraud charges, had agreed last September to cooperate with special counsel Robert Mueller's ongoing investigation into allegations of collusion between Trump's campaign and Russian Federation. It claims an unknown individual texted Manafort about dropping his name if the unidentified person ever met President Trump. The revelations in the court filing Tuesday seem to confirm that.
Kilimnik has always been suspected to be central to Mueller's investigation into Russian influence in the 2016 presidential election.
Image copyright Reuters Image caption Manafort managed the Trump campaign for five months in 2016, during the time Mr Trump clinched his party's nomination What did we learn from the documents?
Manafort and Kilimnik were charged with conspiracy to obstruct justice by attempting to tamper with witnesses after Manafort had been already been indicted for other crimes.
According to The Times, Manafort and Rick Gates, his former business partner and campaign deputy, provided the information in spring 2016, around the time Trump clinched the GOP nomination.
Manafort met Kiliminik in Madrid in January or February 2017, according to Manafort spokesman Jason Maloni.
The lawyers further stated that Manafort's time in solitary confinement has negatively impacted his state of mind, and he was not able to prepare for his meetings with federal prosecutors. But the data could have provided Russians with insights on the US election.
The judge in DC federal court who has overseen his case, Amy Berman Jackson, gave him the opportunity to respond before she would hold a hearing about the facts of the situation.
Manafort, 69, was convicted in August in a separate case in Virginia, for evading taxes on $16m earned as a political consultant in Ukraine and lying to banks to get loans. Manafort "lied in multiple ways and on multiple occasions", prosecutors wrote, saying "these were not instances of mere memory lapses".
Manafort faces a tentative March 5 sentencing date in his federal case in the District.
The inadvertent disclosures offered a rare glimpse into details that were meant to remain private while Manafort's lawyers and Mueller's office battle over whether Manafort has breached a plea agreement struck in September by lying.