WASHINGTON (Reuters) - Thousands of protesters were marching in Washington on Saturday as rallies across the United States to protest the killing of a black man in Minneapolis police custody entered a 12th day and officials moved to rein in law enforcement tactics. George Floyd, 46, died on May 25 in Minneapolis after a police officer knelt on his neck for nearly nine minutes. The killing has triggered protests against racism and police brutality in cities and smaller communities nationwide, as well as demonstrations by supporters around the world.