BREAKING NEWS: The AP is reporting that a United States Capitol police officer has been shot in or around the Capitol Visitor's Center. Reports suggest that the officer is not seriously wounded and the shooter is in custody.
UPDATE: The shooter has been taken into custody. The shooting occurred in the north security check-in area of the U.S. Capitol Visitor's Center. The U.S. Capitol Police have instructed staffers to shelter-in-place.
More details to come.