1. First Shot: Alleged gunman Russell E. Weston Jr. bursts through the metal detector checkpoint and comes up behind Capitol Police Officer Jacob J. Chestnut. Chestnut is giving directions to a 15-year-old boy and his father. Without warning, Weston fatally shoots Chestnut in the back of the head.

2. Flight: Weston moves from the metal detector area, running behind a woman fleeing down the corridor. Capitol Police Officer Douglas B. McMillan fires as Weston runs past. Another woman, identified as Angela Dickerson, 24, is wounded.

3. Warning: Capitol Police Special Agent John Gibson, assigned to protect Majority Whip Tom DeLay (R-Tex.), hears the shots and orders staff to stay in their offices and get down on the floor. The fleeing woman arrives in the doorway, with Weston behind her.

4. Confrontation and Arrest: Gibson shoves the woman away and warns Weston to drop his weapon. Weston shoots Gibson in the chest. Gibson and Weston exchange fire at nearly point-blank range. Weston is shot in both legs and the stomach. Both men collapse. Other officers arrive.

By Brenna Sink, Laura Stanton and Lon Tweeten of The Washington Post and Paul Compton and Mark Hill of washingtonpost.com