WASHINGTON (Reuters) - Senate Republicans say their investigation of Hillary Clinton’s role in approving a deal to sell U.S. uranium mines to a Russian company hinges in part on the testimony of a secret informant in a bribery and extortion scheme inside the same company.

Warning signs are displayed near Uranium One and Anfield's "Shootaring Canyon Uranium Mill" facility sits outside Ticaboo, Utah, U.S., November 13, 2017. Picture taken November 13, 2017. REUTERS/George Frey

The Senate committee searching for Clinton’s alleged wrongdoing is keeping their witness’s name cloaked. However, William D. Campbell, a lobbyist, confirmed to Reuters he is the informant who will testify and provide documents to Congress about the Obama Administration’s 2010 approval of the sale of Uranium One, a Canadian company with uranium mines in the United States, to Russia’s Rosatom.

At the time of the sale, Campbell was a confidential source for the FBI in a Maryland bribery and kickback investigation of the head of a U.S. unit of Rosatom, the Russian state-owned nuclear power company. Campbell was identified as an FBI informant by prosecutors in open court and by himself in a publicly available lawsuit he filed last year.

[Link to page from Campbell lawsuit tmsnrt.rs/2zZhZkM and full complaint tmsnrt.rs/2zXKMWD]

In a telephone interview, Campbell said he wanted to testify because of his concerns about Russia’s activities in the United States, but declined to comment further.

Campbell’s lawyer, Victoria Toensing, who has not previously identified her client, said despite Campbell telling the government “how corrupt the company was,” Rosatom still got permission to buy Uranium One. She did not say what Campbell would reveal regarding any alleged wrongdoing by Clinton.

Clinton has said the Senate probe is an attempt to shift attention away from special counsel Robert Mueller’s investigation into Russia’s alleged role in Donald Trump’s 2016 presidential campaign. As the heat from Mueller’s investigation has intensified, Trump has repeatedly called for an inquiry into Clinton and the Russian uranium deal.

“This latest iteration is simply more of the Right doing Trump’s bidding for him to distract from his own Russia problems,” said Nick Merrill, a Clinton spokesman.

Some people who know Campbell are skeptical that he can shed much light on Uranium One. Two law enforcement officials with direct involvement in the Rosatom bribery case in which Campbell was an informant said they had no recollection or record of him mentioning the deal during their repeated interviews with him.

Also, although both Uranium One and the bribery cases involved Rosatom, the two cases involved different business units, executives and allegations, with little other apparent overlap, Reuters found in a review of the court records of the bribery case.

Campbell countered those who dismiss his knowledge of the Uranium One deal. “I have worked with the Justice Department undercover for several years, and documentation relating to Uranium One and political influence does exist and I have it,” Campbell said. He declined to give details of those documents.

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Reuters was unable to learn when the closed-door testimony has been scheduled.

Trump asked that a Justice Department gag order on Campbell stemming from the bribery case be lifted so that he can testify to congressional investigators, White House officials said.

The Justice Department has partially lifted that gag order.

CAMPBELL TESTIMONY ‘CRITICAL’

Campbell potentially now has a larger starring role in the Washington drama after the Justice Department said in a letter to Congress on Monday that it was considering appointing a special prosecutor to launch an investigation into Republican allegations of wrongdoing by Clinton, Trump’s former political rival, in the deal.

Under Clinton, the State Department was part of a nine-agency government Committee on Foreign Investment in the United States that approved the purchase of Uranium One. Her critics, including Trump, allege large donations by people connected to the Uranium One deal made to her family’s foundation influenced the State Department’s decision to approve it.

Reuters has no evidence that Clinton orchestrated the approval of Uranium One.

In an email, Rosatom said the company had made no donations to the Clinton Foundation and had not asked others to do so. The foundation stressed the State Department was only one member of the committee that approved the deal and said Clinton had no personal involvement in the decision.

Senate Judiciary Committee Chairman Charles Grassley said in a letter to Toensing, Campbell’s lawyer, that her client appears to have information “critical to the Committee’s oversight of the Justice Department and its ongoing inquiry into the manner in which” the Uranium One sale was approved.

BRIBERY SCHEME

Campbell worked as an informant for federal authorities investigating Vadim Mikerin, a Russian official in charge of U.S. operations for Tenex, a unit of Rosatom. Authorities later accused Mikerin of taking bribes from a shipping company in exchange for contracts to transport Russian uranium into the United States. He pleaded guilty in federal court in Maryland and was sentenced to prison for four years.

The Justice Department had also initially charged Mikerin with extorting kickbacks from Campbell after hiring him as a $50,000-a-month lobbyist.

Prosecutors alleged Mikerin had demanded Campbell pay between one-third and half of that money back to him each month under threat of losing the contract and veiled warnings of violence from the Russians. The demand prompted Campbell to turn to the FBI in 2010, which gave its blessing for him to remain part of the scheme.

Federal prosecutors were ready to use Campbell as a star witness against Mikerin, but they backed away after defense attorneys raised questions about Campbell’s credibility and whether he was a victim or had “entered into a business arrangement with eyes wide open,” according to court records.

Before it was taken down last year, the website of Campbell’s company, Sigma Transnational, did not suggest his firm was a lobbying powerhouse. The website listed four other employees and advisers, although one had died years earlier. A second employee listed said in a court document that she never worked for the company but had agreed in 2014 to pay Campbell to list her as an employee and allow her to use the Sigma name in a business deal. Campbell declined to comment on the staffing or his lobbying contract with Tenex.

Prosecutors dropped the extortion charges against Mikerin and never mentioned Campbell again in any charging documents. A Justice Department spokeswoman declined to comment on the case. Campbell also declined to comment on the issue.

Reuters has been unable to learn why Tenex chose Campbell as its lobbyist. He acknowledged in lawsuit he filed in 2016 that he was hired despite the fact he “had no experience with nuclear fuel sales.”