Certain events haunt the consciousness of a generation: the Hungerford massacre, Dunblane. These horrific acts of mass murder are a terrifying reminder that the actions of just one person can devastate the lives of hundreds of others. In the aftermath of a mass killing there is inevitably a stream of questions, but the most common is always "Why?" Bill O'Brien is a retired police officer with first-hand experience of such events. Here he examines nine of the most shocking cases in living memory, including Charles Whitman of Austin, Texas and James Huberty of San Diego, California, and reveals some startling similarities in the psychological profiles of the killers. His fascinating insights and intelligent conclusions shed light on one of the most confusing and sickening of crimes—mass murder.