In “The Kill Switch,” writer Phil Zabriskie, who covered both Iraq and Afghanistan for Time and other magazines, reconnects with two Marines and other veterans he met in Iraq and finds them ready to talk about it and willing to examine soberly and honestly what they’ve done and were asked to do. From boot camp through the initial invasion to the crucible of Ramadi, the siege of Fallujah, and beyond, they recount firefights, ambushes, suicide car bombers, hand-to-hand combat, and the life and death decisions they made about Saddam’s soldiers, battle-hardened insurgents, and people, even children, who were in the wrong place at the wrong time.