Spicer was a zealous notetaker in the White House, sources tell CNN, a habit that dates to his time as the top strategist at the Republican National Committee. Spicer filled notebooks over his eight-month tenure as Trump's spokesperson, taking copious notes as the administration got off the ground.
Now, as special counsel Robert Mueller's investigation into Russia's 2016 meddling begins to broaden and he seeks an array of documents from inside the White House, those notebooks could prove useful to investigators who hope to establish what was happening inside the West Wing at the time.
Multiple White House officials declined to comment on Spicer's note-taking or whether Mueller has asked for Spicer's notes.
The breadth of Spicer's notebooks is an open question. Near the end of his tenure, as the President took a dim view of his press secretary, Spicer was cut out of many high-level White House meetings, meaning his notes, while copious, could be devoid of the most interesting details to Mueller.
It is also unclear whether Spicer could be compelled to hand over his notes or if such writings would be covered under executive privilege, a legal standard dating back to Richard Nixon's administration that protects the President from disclosing internal or confidential communications in the executive branch.
"If the memos are Spicer's own documents in Spicer's possession, then I think it's a close call whether they're protected by privilege," said Steve Vladeck, a CNN legal analyst and a professor of law at the University of Texas. "And all of this assumes Spicer wants to invoke privilege."
Jeffrey Toobin, CNN's senior legal analyst, said any claim of privilege on Spicer's notes would require a judge to weigh "whether the information is central to the functioning of the executive branch" against "the competing need for it from law enforcement or Congress."
"The primary check on the President is political rather than legal, in the sense that presidents don't want to be seen as covering up," Toobin said. "They want to appear to be cooperative and that they have nothing to hide. But if they decide to fight, I think the outcome is not clear at all."
Trump and his senior aides have vowed to be transparent with the Mueller investigation, with the hopes of it ending soon.
Spicer's note-taking struck some former White House officials as odd, given that most administrations that find themselves under investigation caution aides against taking detailed notes because of the possibility that those reflections could be subpoenaed and made public.
"One poor guy got his personal diary subpoenaed and had to read it aloud in front of a Senate committee during Whitewater," a former senior adviser to President Bill Clinton said when asked about whether aides were told to restrict note-taking during the investigation. "So we learned early on not to do that."
The former official was referring to Joshua Steiner, the former chief of staff for Treasury Secretary Lloyd Bentsen, who testified in 1994 about the lessons he would lay out for himself at this end of his regular diary entries.
Sitting before Senate panel investigating the Clintons, Steiner read the end of one of his diary entries.
"Do what you think is the right thing early (recuse); remember that everything might eventually be asked under oath; don't let the WH get involved in any way," he read.
After leaving the White House in August, Spicer has been on a media blitz, looking to rehabilitate his image and credibility after a number of bruising months as Trump's spokesman.
He made a brief appearance at the Emmy's earlier this week, mocking his defense of Trump's inaugural crowds. And on Thursday he appeared on ABC and denied ever knowingly lying to defend Trump.
"I have not knowingly done anything to do that, no," Spicer said, after saying more equivocally that he didn't "think so."