A Russian man who contacted the Trump campaign in May 2016 claiming to be an American citizen named “Hank Greenberg” and offering dirt on Hillary Clinton also worked as an FBI informant for at least 17 years, according to a private investigation undertaken by former Trump campaign adviser Michael Caputo.

Caputo said in a letter he sent to the House Intelligence Committee on Friday that the man, 59-year-old Gennadiy Vasilievich Vostretsov, had reached out to him in late May 2016 through his business partner in Miami, a Russian national named Sergey Petrushin. Vostretsov introduced himself as “Henry Greenberg” and said he had information about Clinton he wanted to provide the Trump campaign.

Caputo put him in touch with Roger Stone, who was serving as a senior adviser to then-candidate Donald Trump and lived in South Florida. Stone met with “Greenberg” but later told Caputo that he had tried to sell information on Clinton, but he declined and thought “Greenberg” was “a nut,” according to the letter.

According to text messages reviewed by the Washington Post, Caputo wrote to Stone: “How crazy is the Russian?” Stone replied that “Greenberg” wanted “big” money. “Waste of time,” he texted Caputo.

Caputo said he forgot about this interaction until several weeks ago, when the Special Counsel asked him about a May 29, 2016, text message he sent to Stone asking if “Greenberg” had contacted him. Caputo said he was suspicious about how much the Special Counsel knew about the “Greenberg” approach and ordered his own investigation of him.

“After my [Office of Special Counsel] interview, I deployed the crowdfunding resources of CaputoLegalFund.com to investigate Henry Greenberg in the United States and Russia,” Caputo said in a statement on Sunday. “We discovered very quickly that this shady character has a long career as an FBI informant.”

Caputo found that “Greenberg” was really Vostretsov and had also assumed the names Henry Oknyansky and Gennady Arzhanik. He learned that Vostretsov had a long history of criminal activity in Russia, served ten years in prison, he first arrived in the U.S. in 1994, was soon after charged with assault with a deadly weapon, and served time in U.S. prisons for that and other charges.

Caputo learned that Vostretsov lived in the U.S. intermittently since 1997 and worked for many of those years as an FBI informant.

“In a 2015 affidavit, Arzhanik admitted to being an informant and working for the FBI in the US, Iran and North Korea. He was reassigned to the FBI Miami field office in 2013 and remains in South Florida,” Caputo’s lawyer said.

Stone, according to a letter his attorney sent Friday to the House Intelligence Committee, met with “Greenberg” at a cafe in Sunny Isles, Florida, at the end of May 2016 for about 20 minutes. “Greenberg” was wearing a Trump MAGA hat and T-shirt and showed Stone pictures of himself at several South Florida Trump rallies.

“Greenberg” then tried to sell “non-specific, damaging” Clinton information for $2 million. Stone told him he did not have that money and that even if he did, he would never pay for political information. “Greenberg” said he was seeking Trump’s money, but Stone told him that Trump would never buy information either. Stone never communicated with him again, the letter said.

Caputo posted a 28-page file on Vostretsov he dubbed the “Greenberg dossier” on DemocratDossier.org.

Caputo and Stone’s allegations come shortly after the exposure in May that another alleged FBI informant, Cambridge University professor Stefan Halper, had reached out to at least three members of the Trump campaign around the same time as Vostretsov’s outreach to Caputo.

Halper had invited former Trump campaign adviser Carter Page in June 2016 to attend a Cambridge symposium on the U.S. presidential election on July 11-12, 2016. There, he introduced himself to Page and the two kept in touch through last fall.

Halper, later that fall but before the election, also reached out to another Trump campaign adviser, Sam Clovis, with an offer to help the campaign. Several days later, he contacted former Trump campaign adviser George Papadopoulos with an offer to pay him $3,000 for a paper on Israeli and Cypriot energy.

Halper flew Papadopoulos to London to discuss the offer and, during a meeting, asked him if he knew about “emails” that Russians had about Clinton. Halper allegedly grew agitated when Papadopoulos said he did not know about any emails.

Papadopoulos had been told in April 2016 by a Maltese professor named Joseph Mifsud that the Russians had dirt in the form of emails that would be embarrassing to Clinton. Several weeks later, Australian diplomat Alexander Downer requested a meeting with Papadopoulos, where Papadopoulos passed on that the Russians had dirt on Clinton. The information somehow got relayed back to the FBI.

Stone’s lawyer said Stone believes the FBI was trying to entrap him and compromise the Trump campaign.

“Mr. Stone believes it is likely that Mr. Greenberg was actively working on behalf of the FBI at the time of their meeting with the intention of entrapping Mr. Stone and to infiltrate and compromise the Trump effort,” the letter from his attorney said.

Vostretsov’s outreach to Caputo and Halper’s outreach to Page both occurred about two months before FBI officials said they received information that prompted them to launch their investigation and suggest the FBI has lied about when it actually began investigating the Trump campaign and why.

Current and former law enforcement officials told the New York Times in December 2017 that they had received the information about Papadopoulos from the Australian diplomat after the release of hacked Democratic National Committee emails on July 22, 2016, which they said prompted them to launch their investigation on July 31, 2016. Mifsud has reportedly gone into hiding.

Committee Chairman Devin Nunes (R-CA) requested information related to the use of informants in April, and on Fox News Sunday, he said he is giving the DOJ and FBI by the end of this week to turn over information before Congress begins taking actions that could include holding the agencies’ leaders in contempt and possibly articles of impeachment.