Federal prosecutors are going to question the chief executive of Ukraine’s state-owned gas company Thursday about his encounters with two associates of Trump’s personal lawyer, Rudy Giuliani, as the two men pursued energy deals in Ukraine. Andrew Favorov, the executive of Naftogaz, agreed to speak with prosecutors for the Southern District of New York about his experiences with Lev Parnas and Igor Fruman. The Washington Post reports that Parnas and Fruman worked with Giuliani to gather information about former vice president Joe Biden and his son Hunter’s business dealings in Ukraine. Federal prosecutors have been investigating Giuliani’s ties to Parnas and Fruman, who were charged with violating U.S. campaign finance laws last month for allegedly helping to funnel foreign money to candidates and political committees. Both Parnas and Fruman have pleaded not guilty.