Unlike many of their fellow Trump supporters, the Proud Boys did not show up for Mr. Trump’s address near the White House on Jan. 6. Instead, they assembled at the Washington Monument around 10 a.m., according to one of the committee’s live witnesses, Nick Quested , a documentary filmmaker who was embedded with the group that day. About 200 members of the group gathered that morning, Mr. Quested said, and marched through the city streets, arriving at the Peace Circle on the west side of the Capitol at shortly before 1 p.m., just minutes before lawmakers inside the building were...