Late one night in the summer of 2005, Matthew Sepi, 20, an Iraq combat veteran, headed out to a convenience store in the seedy Las Vegas neighborhood where he had settled after leaving the U.S. Army.

By day, the area, littered with malt liquor cans, looks depressed but not menacing. By night, it becomes, in the words of a local homicide detective, "like Falluja."

Sepi did not like to venture outside too late. But, plagued by nightmares about an Iraqi civilian killed by his unit, he said he often needed alcohol to fall asleep. And so it was that night, when, seized by a gut feeling of lurking danger, he slid a trench coat over his slight frame - and tucked an assault rifle inside it.

"Matthew knew he shouldn't be taking his AK-47 to the 7-Eleven," Detective Laura Andersen said, "but he was scared to death in that neighborhood, he was military trained and, in his mind, he needed the weapon to protect himself."

As Sepi started home, two gang members, both large and both armed, stepped out of the darkness. Sepi later said that he spied the butt of a gun, heard a boom, saw a flash and "just snapped."
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The New York Times found 121 cases in which veterans of Iraq and Afghanistan committed a killing in the United States, or were charged with one, after their return from war. In many of those cases, combat trauma and the stress of deployment - along with alcohol abuse, family discord and other attendant problems - appear to have set the stage for a tragedy that was part destruction, part self-destruction.