But what exactly is known about the controversial move to ax Comey, and what could it mean for what Mueller’s team is still hoping to uncover? Shifting narratives and conflicting messages about possible intentions and directives before the May firing took place have helped make it all quite murky.
Here is a breakdown of the known facts, and the unanswered questions, about the whole matter.
What the White House said publicly
"President Trump acted based on the clear recommendations of both Deputy Attorney General Rod Rosenstein and Attorney General Jeff Sessions," the White House statement read.
Rosenstein wrote a memorandum, dated May 9, to Sessions, criticizing Comey’s handling of the Clinton email investigation, as well as Comey’s July 5, 2016, news conference on the FBI’s ultimate findings in that probe.
“I cannot defend the director's handling of the conclusion of the investigation of Secretary Clinton's emails, and I do not understand his refusal to accept the nearly universal judgment that he was mistaken,” Rosenstein wrote.
The White House released its statement, a letter that Trump wrote to Comey, including the president’s claim that Comey told him he was not under investigation in relation to the Russia probe, as well as the memos from both Rosenstein and Sessions urging the president to fire Mueller.
"While I greatly appreciate you informing me, on three separate occasions, that I am not under investigation, I nevertheless concur with the judgment of the Department of Justice that you are not able to effectively lead the Bureau," Trump wrote in his letter to Comey.
"It is essential that we find new leadership for the FBI that restores public trust and confidence in its vital law enforcement mission.”
When the official word arrived
Comey's termination was read to him over the phone while he was traveling for the bureau in Los Angeles, two FBI sources told ABC News. He was there for a field office inspection and a recruitment event that evening as part of the FBI's efforts to boost diversity.
A different FBI official told ABC News that Comey first learned of his firing by seeing news reports on TV. Comey was "surprised, really surprised" and was "caught flat-footed," the official said.
A White House official confirmed to ABC News that Keith Schiller, the president's longtime bodyguard and then-Oval Office director of operations, hand-delivered Trump's termination letter to FBI headquarters.
FBI agents and staff were stunned by the news, FBI sources told ABC News.
Motivations for the memo
In the days immediately after Comey’s firing, different White House officials, including Spicer and then-deputy press secretary Sarah Sanders, denied that Trump had influenced or directed Rosenstein to write the memo that suggested Comey be fired.
That differed from other accounts.
On May 10, Sen. Feinstein said that during his call with her, Trump said "the department's a mess, I asked Rosenstein and Sessions to look into it," apparently referring to the FBI.
And in the wake of Comey’s firing, Trump told NBC News, “When I decided to just do it, I said to myself, I said 'you know, this Russia thing with Trump and Russia is a made-up story.’"
How it relates to the Russia investigation
The nature of the interactions and any alleged directives shared between the White House and the key Department of Justice officials before the Comey dismissal is now a part of special counsel Mueller's investigation into Russian interference in the 2016 election.
ABC News has since learned from a source that Mueller's team is eager to obtain emails related to the firing of Comey. Mueller's investigators now seek not only communications between Justice Department officials themselves, but also any communications with White House counterparts, the source said.
During a House hearing in June, Rosenstein refused to say whether he consulted with the White House before Comey's firing or whether anyone asked him to write his memo, insisting such questions "may well be within the scope of the special counsel's investigation."
Rosenstein still maintains final supervision over the Russia investigation being led by Mueller, even though he was interviewed by Mueller's team as a witness for his own role in Comey's firing.