President Donald Trump’s lawyers said that special counsel Robert Mueller, who is leading the Russia investigation, has comprehensive notes taken by a former White House staffer detailing the president’s behavior.

According to a report published on Monday by The New York Times, Annie Donaldson, the chief of staff to former White House counsel Don McGahn, handed over detailed notes about the president’s conduct in the West Wing to the special counsel’s team.

The notes reportedly play a role in Mueller’s investigation into whether Trump obstructed justice by firing former FBI director James Comey or through his various attacks on the Department of Justice. The team also has information gathered from its hours of questioning Steve Bannon and Jared Kushner about the president’s actions.

The president fired Comey in May 2017, initially citing the former FBI director’s mishandling of the Justice Department’s investigation of Hillary Clinton’s private email use. At the time, Comey was leading the inquiry into whether Trump campaign members conspired with Russian government officials in 2016. His firing made Trump only the second president in history to dismiss an FBI director. In a subsequent interview with NBC, Trump said he was thinking of “this Russia thing” when he chose to fire Comey.

Trump’s attorneys told The Times that Donaldson’s notes about the president were a jewel in Mueller’s evidence that Trump may have obstructed justice.