Senate Judiciary Chairman Chuck Grassley is demanding the friend of former FBI Director James Comey hand over official memos he leaked to the media last month, according to a letter released Friday.

The Iowa Republican and a group of bipartisan committee leaders sent a letter to Daniel Richman, a professor at Columbia Law School, asking him to submit all documents that Comey had penned and were later published by the New York Times.

"Mr. Comey's memoranda are relevant to the Judiciary Committee's ongoing investigative efforts. Mr. Comey himself has encouraged you to release them," wrote Grassley, along with ranking member Dianne Feinstein, D-Calif.; Crime and Terrorism Subcommittee Chairman Lindsey Graham, R-S.C.; and ranking member Sheldon Whitehouse, D-R.I.

Comey admitted in a hearing before the Senate Intelligence Committee on Thursday that he had purposely asked a friend who worked at Columbia to leak copies of memos about his interactions with President Trump to trigger the appointment of a special counsel to investigate the campaign's relationship with Russia. Richmond later confirmed to the Washington Examiner that he was Comey's friend at Columbia.

That statement propelled Sen. James Lankford, R-Okla., to ask Comey on Thursday to retrieve those memos.

"It's a good question," Comey replied. "I think so, I guess I can't say for sure sitting here. I guess I don't know, but I think so."

"So the question is, could you ask them to hand that copyright back to you so you can hand them over to this committee?" Lankford asked.

"Potentially," Comey said.

Grassley's committee requested the documents no later than Friday.