A police officer shot a gunman, who was eventually captured, inside the United States Capitol complex in Washington on Monday, according to Reuters via a source from the Sergeant-at-Arms in Congress.

At 2:08 pm on Monday, an unknown assailant carrying a gun entered the visitor center right below the Capitol grounds.

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Gunshots were heard and employees were instructed to take shelter amid confusion. The shooting allegedly occured a few hours after a simulation drill of an active shooter in the Capitol, thus causing perplexity among workers.

Congress was in recess and several lawmakers were present in Washington when the shooting took place.

A U.S. Capitol police officer, who requested anonymity, revealed that the suspect was transported to the hospital after being shot. The officer added that there were no additional suspects and did not provide any identification or description of the suspected shooter.

The police officer, who shot down the suspect, sustained minor injuries. A female civilian was allegedly injured during the shootout.

Caitlyn Leff, a licensed therapist, who was present in the Capitol, shared her experience on Twitter about how she dealt with the situation upon hearing gunshots while going through the security checkpoint.

"Everyone is screaming and running and you can't see where the #ShotsFired are from," tweeted Leff.

The Capitol and neighboring buildings were placed on a lockdown before an all-clear order was issued. The Secret Service cleared the vicinity surrounding the White House after the shooting occurred, but activities were eventually restored back to normal pace.

TagsUS Capitol, shooting, gunman, captured, police officer