JOSH COOKE DOESN'T REMEMBER what he was thinking at 7:30 p.m. on Monday, Feb. 17, when he went up to his room after eating dinner with his parents. He remembers what he was listening to on his headphones -- "Bodies," by metal drones Drowning Pool -- and what he did. "I just kinda looked over at my `Matrix' poster," he says, "and then I looked over at my gun." The 19-year-old donned combat boots and a black jacket -- like Neo, the hero of the 1999 movie and its sequels. He filled his pockets with shotgun shells. Then he picked...