Investigators working for special counsel Robert Mueller have issued a request to the Department of Justice for documents related to the firing of former FBI Director James Comey, ABC News reported late Sunday.
The DOJ had already turned over a letter drafted by the president, but never sent, that "offered an unvarnished view of Mr. Trump's thinking in the days before" he fired Comey, The New York Times reported in September.
That letter became significant for investigators on Mueller's team who were interested in whether Trump fired Comey in an attempt to thwart the FBI-led Russia inquiry, The Washington Post reported at the time.
The letter was blocked by White House counsel Donald McGahn. Deputy Attorney General Rod Rosenstein ultimately wrote a letter sent May 9 that recommended the firing.
According to the ABC News report, Mueller's investigators are also interested in Attorney General Jeff Sessions' March decision to recuse himself from investigations into the presidential campaign.
Sessions sent a letter to the president recommending that Comey be fired two months after recusing himself from any matters connected to the 2016 election. He later said that the suggestion that his recusal should have prevented him from recommending Comey's termination was "absurd."
Sessions was an outspoken supporter of Trump's presidential campaign and led its national security advisory committee.
Sessions was grilled Nov. 14 at a congressional hearing, after the first court documents filed in connection with the Russia probe appeared to show that he had been told about Trump campaign officials' communications with representatives for Russian President Vladimir Putin.
Sessions had earlier denied any such connections between the Trump campaign and Russia in sworn testimony to Congress. Trump has also repeatedly denied any collusion between his campaign and the Russian government.
"I do now recall that the March 2016 meeting at the Trump hotel that Mr. Papadopoulos attended, but I have no recollection of the details of what he said at that meeting," Sessions told lawmakers.
Despite saying that he didn't recall details of the meeting with George Papadopoulos, a former Trump campaign foreign policy advisor, Sessions said he "pushed back" against Papadopoulos' offer to arrange a meeting between Trump and Putin.
Papadopoulos has pleaded guilty to charges of lying to the FBI about contacts with Russian nationals.
Sessions was also told of a planned trip to Moscow by campaign advisor Carter Page, according to a transcript released by the House intelligence committee. Sessions said he didn't challenge Page's account but that "I have no memory" of the interaction.
A spokesperson for the special counsel's office declined to comment to CNBC. The Department of Justice did not respond to a request for comment.