TUCSON — Moments after the swirl of panic, blood, death and shock, the suspect was face down on the pavement and squirming under the hold of two civilians, his shaved head obscured by a beanie and the hood of his dark sweatshirt. Deputy Sheriff Thomas Audetat, a chiseled former Marine with three tours in Iraq to his credit, dug his knee into the gangly young man’s back and cuffed him. With the aid of another deputy, he relieved the heroic civilians of their charge and began searching for weapons other than the Glock semiautomatic pistol, secured nearby under a civilian’s...