Former White House spokesman Sean Spicer was known to take detailed notes of his time in the White House, which could be targeted by special counsel Robert Mueller, who is reportedly seeking to interview Spicer as he investigates the Trump administration's ties to Russia.

Spicer filled "notebook after notebook" during his time at the Republican National Committee, the Trump campaign and at the White House, according to a report Thursday morning.

Spicer's former colleagues told Axios that the former White House press secretary was well known for taking a lot of notes during meetings. "Sean documented everything," one source said in the report.

"People are going to wish they'd been nicer to Sean. ... he was in a lot of meetings," a White House official told Axios.

Spicer refused to answer further questions about the notes he took while in the White House. He asked Axios to stop texting him, and said in an email that he would see further texts and emails to him as harassment.

"Please refrain from sending me unsolicited texts and emails," Spicer told Axios' Mike Allen in an email. "Should you not do so I will contact the appropriate legal authorities to address your harassment."

Mueller has indicated that the White House should expect his team to interview Spicer and other top former and current aides in the Trump administration.

Mueller's team has already asked the White House for documents involving former national security adviser Mike Flynn, including a warning from Justice Department on his ties with a Russian diplomat, according to a Wall Street Journal report.

Spicer was involved in the matter with Flynn before Trump's inauguration. After Flynn contacted former Russian Ambassador Sergei Kislyak in December, he informed top Trump officials that the topic of U.S. sanctions against Russia did not come up.