WASHINGTON – Samuel Patten, a longtime Washington operative and associate of a Russian-Ukrainian man indicted by Special Counsel Robert Mueller, has admitted to lobbying for a Ukrainian political party and failing to register as a foreign agent.

Patten’s guilty plea, entered August 31 in a Washington, D.C., federal court, also included the admission that he helped the Russian-Ukrainian man, and another foreigner, illegally obtain four tickets to President Donald Trump’s inauguration in January 2017 at a cost of $50,000.

Patten entered the plea just hours after the U.S. attorney for the District of Columbia unveiled a multicount criminal complaint against him.

Earlier this week, Patten, who faces up to five years in prison and a $250,000 fine, declined an interview request from RFE/RL.

The plea was the latest development to emerge from Mueller’s sprawling criminal investigation into Russian interference in the 2016 presidential election and interactions between Russian officials and Trump’s campaign chairman.

The charges brought against Patten were not filed by Mueller’s prosecutors but rather by the U.S. attorney for the District of Columbia, though they overlap with several of the issues -- and individuals -- that Mueller has been probing.

According to the complaint filed in federal court, Patten worked on behalf of the Ukrainian political party Opposition Bloc between 2014 and 2018, without disclosing the work to the U.S. government as required under the Foreign Agents Registration Act.

The complaint says that Patten worked with a person identified only as Foreigner A as part of the lobbying and political consulting business. Patten, and Foreigner A, set up a company in the United States that was paid more than $1 million to work on behalf of Opposition Bloc.

The details of Foreigner A’s activities match up with those of Konstantin Kilimnik, a Russian-Ukrainian dual citizen whom Mueller has alleged has ties to Russian intelligence agencies.

According to prosecutors, in early 2017, Foreigner A asked Patten for help in obtaining tickets for Trump’s inauguration on behalf of another person, identified only as Foreigner B.

Patten then worked to find an American citizen to purchase the tickets for $50,000 in total, as a way to circumvent U.S. law, which widely prohibits foreigners from contributing to political activities.

Kilimnik’s name first appeared in court papers publicly when he was charged by Mueller with witness tampering, along with another longtime lobbyist, Paul Manafort.

Manafort, who was fired as Trump’s campaign chairman in August 2016, was convicted by a federal jury in Virginia on tax and bank fraud stemming from his work between 2010 and 2014 for the pro-Russia Ukrainian political party Party of Regions and then-President Viktor Yanukovych.

Manafort later did consulting work for Opposition Bloc, which was set up by former members of the Party of Regions and their financial backers after Yanukovych fled the country in February 2014 amid mass street protests.

Manafort faces a second trial in September in Washington, where the charges filed by Mueller include conspiracy to defraud the United States, witness tampering, and failing to register as a foreign agent.

That charge stems from Manafort's work both for the Party of the Regions but also the Opposition Bloc, now a minority party in Ukraine's parliament.

At the time Mueller filed the witness-tampering charges against Manafort, he also filed similar charges against Konstantin Kilimnik, who served as Manafort’s point man in Ukraine. Mueller alleged that Kilimnik has ties to Russian intelligence agencies.

Kilimnik is not referred to by name in the court papers filed on August 31, which state only that Patten worked with a Russian national on political consulting, identified as Foreigner A. But the details match up with much of what is known about Kilimnik's work in Ukraine and elsewhere.

The court papers charged that Patten, and Foreigner A, set up a company in the United States that was paid more than $1 million to work on behalf of Opposition Bloc.

The court filing also detailed Patten's alleged work with another person, identified only as Foreigner B. Patten helped the person draft op-ed articles and get them published in U.S. media in February 2017.

On February 6, 2017, the magazine U.S. News & World Report published an op-ed by Serhiy Lyovochkin, a Ukrainian parliamentary deputy with the Opposition Bloc whose payments to Manafort were detailed during Manafort's trial in Virginia.

He also worked in Georgia, where he said he advised the Free Democrats, a political party headed by former Defense Minister Irakli Alasania. And he worked in Kazakhstan, where he consulted for multinational companies like Coca-Cola and Texaco and reopened the country office for the International Republican Institute, a nongovernmental civil society group that promotes democracy and elections.

From 2001-04, he headed the Moscow office for the IRI, where Kilimnik worked until he was fired in 2005, when officials found he had been also working for a Kremlin-connected oligarch, Oleg Deripaska.

Mueller's investigation has resulted in charges against 32 people, including Trump's first national security adviser, Michael Flynn. The investigation also led to guilty plea by Trump's longtime personal lawyer, Michael Cohen, in a case brought by the U.S. attorney's office in Manhattan.