Deportees from U.S. feed the violence of groups targeted in disputed crackdown. ILOPANGO, El Salvador — Minutes after hooded commandos stormed his tiny shack in the middle of the night and hustled him off to jail, Juan Carlos Diaz was smiling. Had he shot a bus fare collector in cold blood before 25 horrified commuters, as the police said? The 18-year-old high school dropout grinned before answering: "Not even close." But he acknowledged joining the M-18 gang four months earlier and proudly looked down at the 10-inch-high "18" tattooed on his chest and abdomen. "For me," he said, "that number...