Special Counsel Robert Mueller departs after briefing members of the U.S. Senate on his investigation into potential collusion between Russia and the Trump campaign on Capitol Hill in Washington, U.S., June 21, 2017. REUTERS/Joshua Roberts/File Photo

WASHINGTON (Reuters) - Prosecutors for U.S. special counsel Robert Mueller visited a federal magistrate in Washington on Friday to return a grand jury indictment, CNN reported, citing an itinerary posted outside the courtroom.