Jerome Corsi, 72, a conservative commentator, conspiracy theorist and one-time researcher for Mr Stone, confirmed he was in negotiations with the office of the special prosecutor, who is investigating alleged links between the Trump campaign and Russia as part of a wider investigation into apparent election meddling by Moscow.
“I’m going to be criminally charged,” Mr Corsi, who once worked for the Infowars, an outlet that promotes conspiracy theories, said this week during a YouTube livestream. “As of today, right now, I expect to be indicted.”
Mr Corsi said he had been cooperating with FBI agents for several months, after they served him with a subpoena two days before his 72nd birthday. “It was one of the most frightening experiences of my life," he said.
In recent months, a flurry of reports suggested Mr Mueller’s team was focusing on what Mr Corsi knew about Mr Stone’s possible links to WikiLeaks.
American intelligence agencies have claimed Russia was the source of hacked material released by WikiLeaks during the 2016 election that damaged Hillary Clinton’s campaign. Moscow has denied the allegations.
Mr Mueller’s office is trying to determine whether Mr Stone or other associates of President Donald Trump had advance knowledge of WikiLeaks’ plans.
On Friday, both the Associated Press and Reuters reported Mr Corsi had told them he was in plea deal negotiations with Mr Mueller, but declined to provide specifics. “There are plea negotiations going on. I can’t elaborate any more than that,” he told Reuters.
Mr Mueller has been seeking to ascertain the nature of any relationship Mr Stone, a veteran political operative, had developed with WikiLeaks. Earlier the month, he told the AP: “I had no advanced notice of the source or content or the exact timing of the release of the WikiLeaks disclosures.”
Both he and WikiLeaks have denied being in direct contact. But his comments appear to be add odds with remarks he made two years ago.
“I actually have communicated with Assange,” Mr Stone said in a speech in Florida on August 8 2016, referring to WikiLeaks founder Julian Assange. “I believe the next tranche of his documents pertain to the Clinton Foundation but there’s no telling what the October surprise may be.”
Then, on August 21 2016, Mr Stone tweeted: “Trust me, it will soon [be] Podesta’s time in the barrel.” :Less than two months after that, WikiLeaks began posting online emails stolen from the account of Hillary Clinton campaign chairman, John Podesta.
Mr Stone has also acknowledged exchanging direct messages on Twitter in August and September 2016 with Guccifer 2.0, who claimed to be a Romanian hacker. Mr Stone has said there is no proof the account was connected to the Russians.
However, according to criminal charges filed this summer by Mr Mueller against a dozen Russian military intelligence officers of conspiring to hack the Democrats during the 2016 presidential campaign, the handle was in reality operated a group of Moscow-based Russian operatives. The documents said the Russians used Guccifer 2.0’s Twitter account to send multiple messages to “a person who was in regular contact with senior members” of the Trump campaign.
Meanwhile, the Washington Post recently reported that last month, Randy Credico, a onetime Stone friend, told the grand jury that the Trump loyalist confided during the 2016 campaign that he had a secret back channel to WikiLeaks, according to a person familiar with the matter.
Mr Stone has since said his claim about information about Mr Podesta about to made public, was a reference to so-called “opposition research” that Mr Corsi prepared for him about the business dealings of Mr Podesta and his brother, Tony.
In September 2017, Mr Stone appeared before the House of Representatives’ intelligence committee in a closed down session. He later told reporters he had refused to divulge the identity of the person who had been his intermediary with Wikileaks.
“I expressed my view that I’m aware of no evidence whatsoever of collusion by the Russian state or anyone in the Trump campaign or anyone associated with Donald Trump,” Mr Stone said.
On Friday, in a statement provided to The Independent by his lawyer, Grant Smith, Mr Stone said: “As one can see from his recent videos and his recent interviews my friend Dr Corsi has been under a tremendous amount of pressure and it is beginning to affect him profoundly.
“He has stated publicly that he is being asked over and over to say things he simply does not believe occurred. I am not aware of any plea talks involving Dr Corsi, he is an investigative journalist whose activities I would think would largely be covered under the first amendment.”
Last week, it emerged US prosecutors were also preparing to pursue a criminal case against Mr Assange, who has claimed asylum in the Ecuadorian Embassy in London since 2012.
Peter Carr, a spokesman for the special counsel, declined to comment on the reported plea deal talks.
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