(Bloomberg) — A former associate of Paul Manafort pleaded guilty to a lobbying violation and agreed to cooperate with the U.S., giving prosecutors access to insights from a longtime international political operative whose Russian business partner has already been indicted in Special Counsel Robert Mueller’s probe.

The lobbyist, Sam Patten, 47, admitted that he failed to register in the U.S. as a foreign agent for his work lobbying on behalf of a Ukrainian political party. The nature of his cooperation isn’t clear. Patten worked with Manafort and on Ukrainian campaigns, and reportedly worked on microtargeting operations with Cambridge Analytica.

Mueller’s office referred the prosecution to U.S. Attorney Jessie Liu in the District of Columbia, according William Miller, a spokesman for Liu, who declined to comment about the nature of the cooperation or other matters relating to an ongoing investigation.

Patten appeared in federal court in Washington on Friday. No date has been set for his sentencing.

Patten, who served in the State Department under George W. Bush, headed the Moscow office of the International Republican Institute in the early 2000s. A Russian employee of IRI at the time, Konstantin Kilimnik, went on to work as a fixer for Manafort in Ukraine and is a business partner with Patten.

Kilimnik has been indicted in absentia alongside Manafort on obstruction of justice charges. Manafort, who was one of President Donald Trump’s campaign chairmen, was found guilty this month in Alexandria, Virginia, of tax and bank fraud charges. Manafort is due to stand trial in Washington next month on the obstruction charges as well as charges of money laundering and failure to register for his own lobbying work in Ukraine.

Manafort’s Second Trial Looms, and There May Still Be Third

Patten entered his plea before U.S. District Judge Amy Berman Jackson, the same judge who’s overseeing Manafort’s money-laundering and obstruction of justice trial in Washington, scheduled to start next month.

Watching from the gallery was Andrew Weissmann, an expert on money laundering and complex fraud cases who will be the lead prosecutor in Manafort’s trial in Washington. Also in attendance was Scott Claffee, a trial lawyer in the Justice Department’s National Security Division.

From 2014, Patten provided a “prominent” Ukrainian oligarch who isn’t named in court papers and his Opposition Bloc political party with lobbying and consulting services, according to the criminal information. A company Patten co-owned with a Russian national received more than $1 million for the work, the U.S. said.

Details about the Ukrainian oligarch match those of Sergei Lyovochkin, an Opposition Bloc leader whom prosecutors have previously identified as funding Manafort’s work in Ukraine. He couldn’t immediately been reached for comment.

As part of his lobbying work, Patten violated the Foreign Agents Registration Act by not disclosing the work to the U.S., prosecutors said.

Cambridge Analytica

Patten worked for multiple political parties and office-holders in Ukraine, according to his website. His work for Cambridge Analytica came during the 2014 election cycle, the Daily Beast reported in April. It was later adopted by “at least one major U.S. presidential candidate,” the Daily Beast said. Patten told the publication that his work for Cambridge Analytica was separate from the work of his consulting firm.

Cambridge Analytica Files U.S. Bankruptcy After Data Scandal

Patten formed a consulting firm in 2015 with Kilimnik, whom Mueller indicted in June. Kilimnik has been identified in filings as having worked for the Russian military’s intelligence service known as the GRU. One filing cited an FBI assessment that his relations to the GRU continued through the 2016 election, which Kilimnik has denied.

The firm that the two set up, Begemot Ventures International Ltd., listed Patten and Kilimnik as the sole officers, according to its Washington, D.C., incorporation records. The company’s website describes it as “a strategic and political advisory firm that helps its clients win elections, strengthen political parities, build the right arguments before domestic and international audiences and achieve better results.”

Begemot, which is Russian for behemoth, matches details of the unidentified firm that prosecutors say received cash for Patten’s Ukraine work.

Patten registered with Congress in 2016 to lobby for a group called the Committee to Destroy Isis, which was financed in part by a Jordanian construction company, according to disclosures filed with the Senate Office of Public Records. He disclosed payments of $50,000 and stopped lobbying for the group in July.

It’s unclear why Mueller referred the case. Previously, he referred information about Trump’s former personal lawyer Michael Cohen to the U.S. attorney in Manhattan. In July, Deputy Attorney General Rod Rosenstein said the Justice Department’s national security division would take over responsibility of a case filed against a dozen Russian military intelligence officers accused of hacking into the Democratic National Committee and Hillary Clinton’s campaign.

“It may have to do with the size of the case, the nature of the case, the resources needed for the case,” said Mike Koenig, a former Justice Department prosecutor.

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