Halliday put up his hand to stop him. He'd been taught long ago to trust his own instincts, the same instincts that went all the way back to the brief time in his career when he'd worked with the agents who had invented a new way to track serial killers. These agents studied them; they interviewed them; they took them through every case, going over every detail. They got inside their heads, even if that was the last place you'd ever want to be.