As moral dilemmas go, the quandary faced by Tucson soldier Justin Watt was about as gut-wrenching as it gets. A few months ago, the 23-year-old Army private first class began to suspect that fellow soldiers — his "brothers" as he called them — had killed an innocent Iraqi family after raping a 14-year-old girl. Watt thought of all the hell his platoon had endured together in the hostile neighborhoods around Baghdad. For nine months, they'd been dodging bullets and grieving side by side as one member after another was killed in action. But in the end, Watt — who attended...