Torresola approached Blair House, located on Pennsylvania Avenue, from the west side, while Collazo walked up behind Capitol police officer, Donald Birdzell, who was standing on the steps of the Blair House. President Truman was napping in his quarters on the second floor. Collazo tried to shoot Birdzell in the back, but had failed to chamber a round in his pistol, and the gun did not fire. Collazo chambered a round and fired the weapon just as Birdzell was turning to face him, and shot the officer in his right knee.