Alex van der Zwaan, who worked with Mr. Gates and Mr. Kilimnik on a report used to defend Mr. Yanukovych against accusations of prosecuting a rival for political purposes, cooperated with Mr. Mueller’s team before he pleaded guilty in February to lying to investigators. A former lawyer with the international firm Skadden, Arps, Slate, Meagher & Flom, he was sentenced to 30 days and a hefty fine.
Other former associates who have cooperated with Mr. Mueller’s team include employees from the lobbying firms Mercury Public Affairs and the Podesta Group, both of which worked for a nonprofit based in Brussels called the European Center for a Modern Ukraine, which was overseen by Mr. Manafort.
The effort complemented the one with which Mr. Friedman and Mr. Sager were involved from 2011 until 2014 to enlist prominent European politicians to vouch for Mr. Yanukovych. From overseas bank accounts, Mr. Manafort funneled $2.4 million to fund the activities of the coalition overseen by Mr. Friedman and Mr. Sager, which helped place op-eds in the Western news media and arrange speaking engagements.
Mr. Sager, for example, worked with Mr. Manafort and others to arrange a March 2013 visit to Washington by Romano Prodi, the former prime minister of Italy and the former president of the European Commission. Mr. Prodi met with key members of Congress, including Representative Ed Royce of California, the chairman of the House Foreign Affairs Committee, and Representative Eliot L. Engel of New York, the committee’s ranking Democrat.
Mr. Friedman helped prepare an Op-Ed by Mr. Prodi that was published by The New York Times in February 2014, according to prosecutors. The piece argued that Mr. Yanukovych could bring Ukraine back from the brink of collapse and that European leaders should not threaten sanctions against him or the nation.
The day after the commentary was published, Mr. Yanukovych fled Ukraine amid protests of his government’s corruption and pivot toward Moscow, eventually arriving in Russia and effectively ending his presidency.
In an interview on Thursday, Mr. Prodi said that he wrote the Op-Ed, although he acknowledged that he and Mr. Friedman, whom he said he knew only as an author and columnist and not as a lobbyist, had “exchanged views” and maybe “some language.” He added, “When I write an article and sign this document, it’s my responsibility.” He said that he had no knowledge of Mr. Manafort’s involvement, but, after checking his records, he confirmed that Mr. Sager “arranged my appointments in Washington.”