When Severson encountered Walker, Walker was with his mother, who had just returned home from grocery shopping, and his sister, both of whom pleaded with Walker to comply with officers, Mahoney and Fitchburg Assistant Police Chief Donald Bates said.

According to Mahoney, Severson believed that Walker - who was reaching behind his back - had a gun, so Severson drew his gun and ordered Walker to the ground. But Walker charged at Severson, who fired one shot, presumably striking Walker when he was less than 5 feet from him. Almost simultaneously, Walker tackled Severson to the ground and knelt on his arms, pinning them.

As they struggled, Severson managed to point his gun at Walker and fire again, but Walker continued to beat him in the face and head, Mahoney said, adding that as Severson was on the verge of losing consciousness, he was able to position his gun close to Walker's chest and fire.

It is not known how many shots Severson fired the second and third times, but they equaled six, Mahoney said, adding that Severson immediately began performing first aid on Walker.

No gun was found on Walker, and the gun he reportedly had in Fitchburg has not been recovered, Mahoney said. Ozanne said statements from witnesses, including Walker's family members, supported the deputy's account of the attack.