Federal authorities on Thursday began charging what they expect will be dozens of people after thousands of pro- Trump rioters stormed the U.S. Capitol, including one man they said was armed with a semiautomatic weapon and 11 Molotov cocktails and another accused of punching a police officer.

Investigators vowed to find and punish others involved, scouring hotels in the Washington, D.C., area and combing social media and cellphone records for clues to their identities.

“This was obviously a very dangerous situation and we’re aggressively trying to address these cases as soon as possible,” Michael Sherwin, acting U.S. attorney for the District of Columbia, said during a news conference. He said 15 criminal complaints would likely be filed in federal court by the end of the day.

Asked if prosecutors were examining any role President Trump may have had in inciting the violence, Mr. Sherwin said only that “we’re looking at all actors here, and anyone that had a role, and if the evidence fits the elements of a crime, they’re going to be charged.”