In their effort to discredit President Donald Trump's perceived enemies, close allies of the U.S. president have received key documents and information from a Ukrainian oligarch wanted in the U.S. on corruption charges, according to five people directly involved in this effort and two other people familiar with it.

The information came from the legal team of Dmitry Firtash, a wealthy industrialist with assets across Europe, who has spent the last five years in Vienna fighting extradition to the U.S. on bribery and racketeering charges. The U.S. Department of Justice said in 2017 he was among the "upper echelon associates of Russian organized crime" – something Firtash vigorously denies, along with all charges against him, TIME wrote.

As part of his legal defense, Firtash's lawyers have gathered documents that make controversial allegations against former special counsel Robert Mueller and former Vice President Joe Biden. Firtash's lawyers have passed these documents and other information to associates of Trump's personal lawyer Rudy Giuliani.

In his frequent appearances on cable news, Giuliani has presented some of these documents to the American public as evidence for his claims of wrongdoing by Mueller and Biden. The key document is an affidavit from a former Ukrainian prosecutor who accuses Biden of corruption. "The witness I'm relying on," Giuliani told Fox News on Oct. 6, was the prosecutor Viktor Shokin. "That's the affidavit I put out," Giuliani added. He did not mention that the affidavit was obtained by the Firtash legal team. At the beginning of the document, Shokin writes that he is making the statement "at the request of lawyers acting for Dmitry Firtash."

Asked about his ties to the Firtash legal team, Giuliani wrote in a text message to TIME on Tuesday: "I do not represent Mr. Firtash and I have never met him." He did not reply to requests for further comment.

This alignment of interests has taken shape at the same time, and with many of the same goals and actors, as the parallel effort by Trump and Giuliani to pressure Ukraine into investigating Biden's family. The effort in Ukraine was brought to light in September in a complaint from an intelligence-community whistleblower. It is now the subject of an impeachment inquiry in Congress into alleged abuse of office by President Trump.

None of the inquiry's public proceedings so far have mentioned the assistance that Firtash's lawyers have provided to Giuliani. While they have said some documents from the Firtash case would be useful to Trump as a defense against his critics, the lawyers told TIME this summer that the purpose of the documents is to prove their client's innocence. Firtash's legal team has not responded since September to numerous requests for comment about their relationship with Giuliani.

Firtash has established close ties to the former mayor of New York City in part by recruiting several of Giuliani's associates. In July the oligarch hired two lawyers who have been helping Giuliani in his campaign to discredit Trump's critics: Victoria Toensing and Joseph DiGenova, a married couple Trump considered hiring in 2018 as part of his private legal team. Best known as diehard defenders of Trump on Fox News, the couple has combed through the oligarch's case files and used some of them in the effort to defend Trump on television and in the press.

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Toensing and DiGenova then hired another Giuliani associate, Lev Parnas, to serve as their interpreter in communications with Firtash in Vienna, according to a statement the lawyers sent TIME on Oct. 11. While on his way to Vienna on Oct. 9, Parnas was arrested at Dulles Airport in Washington and charged with violating campaign finance laws. The indictment against him alleges that Parnas and his business partners secretly channeled money from an unidentified Russian donor to various political causes and candidates. Parnas has not entered a plea. His colleagues in the Firtash legal team declined to comment on the arrest.

In an interview with NBC News on Monday, Giuliani said he has "nothing to do with Firtash." He also denied ever speaking to Trump about the Firtash case. "I'm not even sure the president is aware of him," Giuliani told NBC. "I think if you asked the president ‘who is Dmitry Firtash?' He would say ‘I don't know.' As far as I know, we've never discussed him."

In acting for Firtash, Toensing and DiGenova's stated aim has been to prevent their client's extradition to the U.S. In a phone interview with TIME on July 31, soon after joining the legal team, they said he should never risk facing an American jury. "Trust me, it would be a disaster," Toensing said. "That's called a riverboat gamble," added her husband.

But the lawyers spent much of the interview talking about one of their favorite topics: the alleged abuses of the special counsel's office. They claimed that one of Mueller's top deputies in the special counsel investigation, Andrew Weissmann, offered to drop the bribery case against Firtash in 2017 in exchange for testimony that could be damaging to President Trump. This, they claimed, would amount to suborning perjury.

They declined to provide documents to back up those claims. In a piece published on July 22, John Solomon, a columnist for the Hill, cited documents from the Firtash legal team to suggest that Weissmann's attempts to turn Firtash were "wrapped with complexity and intrigue far beyond the normal federal case."

Weissmann, now a fellow at New York University's law school, did not respond to emails seeking comment. During his testimony before Congress in July, Mueller bristled at Republican attempts to question Weissmann's integrity, saying he was "one of the more talented attorneys we have on board."

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Documents from the Firtash case have become even more useful to Giuliani and Trump as they roll out their response to the impeachment inquiry. At the center of Giuliani's counterattack so far is the affidavit signed by Shokin, Ukraine's former prosecutor general, which alleges that Biden caused Shokin's dismissal in order to stop a corruption probe into Burisma, a Ukrainian gas company. Biden's son Hunter sat on the board of that company for about five years, reportedly earning $50,000 a month.

"I was forced to leave office, under direct and intense pressure from Joe Biden and the U.S. Administration," in order to stop that investigation, Shokin said in the affidavit, which was notarized in Kyiv on Sept. 4.

These claims have not stood up to scrutiny. Officials in the U.S. and Ukraine, as well as independent experts and investigative journalists, have said Shokin was fired because of his lax approach to fighting corruption. Shokin's successor as prosecutor general, Yuriy Lutsenko, has also said there is no evidence of wrongdoing by the Bidens in Ukraine.

But Giuliani's defense of Trump amid the impeachment inquiry has relied heavily on the statement that Firtash's legal team obtained from Shokin. After reading some of its claims against Biden during an appearance on ABC in late September, Giuliani exclaimed, "That's under oath!".