Mueller's team has reportedly looked into whether Corsi knew in advance that WikiLeaks received Hillary Clinton campaign chairman John Podesta's emails. Corsi denied that he knew ahead of time about the hacking and release of Podesta's emails. He told NBC that he determined they would be released after finding few of the campaign chief's emails in prior dumps of Democrats' communications.
Corsi said that in his statement to the special counsel, he "forgot almost everything about emails in 2016," NBC reported Monday.
"They want me to say I willfully lied. I did not intentionally lie to the special counsel. I'm not going to agree that I lied. I did not," Corsi said. "I will not lie to save my life. I'd rather sit in prison and rot for as long as these thugs want me to."
Corsi said the special counsel told him he "willfully lied on an amended statement," a characterization he disputes.
Corsi said last week that he was in plea negotiations with the special counsel. David Gray, his attorney, had previously said that he suspected the special counsel's questions would be focused on Corsi's communications with Stone.
Stone had presented himself to Trump campaign-related people as being privy to WikiLeaks' inner workings, according to copies of his emails and text messages that have been made public by various news outlets. But he has since denied that he had direct knowledge of WikiLeaks' plans.
Gray and spokesman for the special counsel's office declined to comment. Corsi did not immediately respond to multiple requests for comment on the NBC report.
A White House correspondent for One America News Network, the right-wing media outlet that sided with Trump over CNN in a recent lawsuit, reported earlier Monday about the plea bargain. She also tweeted that Corsi "is preparing to file a CRIMINAL COMPLAINT against Mueller's Investigation with acting Attorney General WHITAKER."
Matthew Whitaker, appointed by Trump to replace former Attorney General Jeff Sessions temporarily, is now overseeing the Mueller probe, according to the Justice Department. Sessions had recused himself from the role — a decision that led to Trump's sharp criticism of him — handing oversight of the probe to Deputy Attorney General Rod Rosenstein.
The DOJ did not immediately respond to CNBC's request for comment on One America's report.
While Corsi is considered a fringe figure in the Republican Party, several of his smears and conspiracy theories have reached the mainstream over the years, including the "Swift Boat" campaign against Democratic presidential nominee John Kerry in 2004.
Corsi is best known for his 2011 book, "Where's the Birth Certificate?" in which he argued that Obama was not eligible to be president. He helped stoke what became known as the "birther" movement, which falsely claimed that the former president wasn't a natural-born citizen of the United States. Trump himself pushed the theory, and it helped propel him to the front line of Republican politics.