In the chaotic minutes before he shot and killed Ashli Babbitt during the Capitol riot on Jan. 6, Lt. Michael Byrd focused his attention on the glass doors leading into the lobby of the House of Representatives chamber.

About 60 to 80 House members and staffers were holed up inside, and it was Byrd's job to protect them.

As rioters rampaged through the Capitol, Byrd and a few other officers of the U.S. Capitol Police set up a wall of furniture outside the doors.

"Once we barricaded the doors, we were essentially trapped where we were," Byrd said in an exclusive interview with NBC News' Lester Holt, speaking publicly for the first time since the riot. "There was no way to retreat. No other way to get out.

"If they get through that door, they're into the House chamber and upon the members of Congress," added Byrd, who gave NBC News permission to use his name after authorities had declined to release it.

Byrd's connection to what was going on outside and inside the building was his police radio. For several minutes, it crackled with a cascade of alarming messages.

There were shouts of officers down. Screams from his colleagues under attack by rioters with chemical agents. A report that an officer's fingertips were blown off.