WASHINGTON (AP) — Former Trump campaign chairman Paul Manafort shared polling data during the 2016 presidential campaign with a business associate accused of having ties to Russian intelligence, and prosecutors say he lied to them about it, according to a court filing.

The allegation marks the first time prosecutors with special counsel Robert Mueller’s office have accused Trump’s chief campaign aide of sharing election-related information with his Russian contacts. Although the filing does not say whether the polling information was public or what was done with it, it raises the possibility that Russia might have used inside information from the campaign as part of its effort to interfere with the election on Trump’s behalf.

The accusation could be important evidence in Mueller’s ongoing probe into potential coordination between the Trump campaign and the Kremlin.

The information was accidentally revealed in a defense filing Tuesday and was meant to be redacted. The Associated Press was able to review the material because it wasn’t properly blacked out.

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, Russia was working to sway the election in Trump’s favor. Manafort has pleaded guilty to conspiracy charges in Washington and faces sentencing in a separate case in Virginia.

The defense filing was aimed at rebutting allegations that Manafort intentionally lied to Mueller’s team after agreeing to plead guilty last September. Prosecutors say Manafort breached their plea agreement by lying, but defense lawyers argued that any misstatements were simple mistakes made by a man coping with illness, exhaustion and extensive questioning from investigators.

The defense lawyers said Manafort suffers from depression and anxiety, has had little contact with his family and, on days when he met with investigators, was awakened before dawn to have hourslong interviews with little time to prepare for the questioning.

“These circumstances weighed heavily on Mr. Manafort’s state of mind and on his memory as he was questioned at length,” the lawyers wrote.

Tuesday’s filing revealed the first extensive details of what he is accused of having lied about. A spokesman for Manafort’s defense team declined to comment on the incomplete redactions or on Mueller’s allegations, but lawyers later filed a corrected version of the document.