Federal prosecutors in Manhattan are looking into Rudy Giuliani's personal business relationships with Ukraine, the Wall Street Journal reports.

The big picture: The investigation is reportedly headed by the southern district of New York's U.S. attorney’s office. Investigators are questioning Giuliani's relationships with Igor Fruman and Lev Parnas, who were arrested last week and charged with violating campaign finance laws and conspiracy. Officials claim the men misrepresented the sources of campaign donations.