It turns out that Capitol Police already knew this guy. From the Daily Beast:
ABC and NBC News report police have identified Larry Dawson of Antioch, Tennessee as the gunman who allegedly drew a gun at the visitors center on Monday. Dawson was shot by a police officer and taken to the hospital. In October, Dawson was caught yelling he was a “prophet of God” from the balcony of the House of Representatives. Dawson reportedly was charged with with unlawful misconduct and assault on a police officer.
#BREAKING No officer shot in Capitol incident. Unfolded inside Capitol Visitor’s Center on north (Senate) side. Suspect came in w/gun
— Chad Pergram (@ChadPergram) March 28, 2016
#BREAKING Sources tell me suspect’s gun set off mags at Capitol Visitor’s Center. 2 officers began shooting. Suspect & bystander wounded — Chad Pergram (@ChadPergram) March 28, 2016
#BREAKING USCP Chief Verderosa says the system worked protecting the Capitol. Suspect was a regular. Suspect in surgery now
— Chad Pergram (@ChadPergram) March 28, 2016