20 April 1999, Columbine High School, Colorado, USA. Lunchtime. Enter Eric Harris and Dylan Klebold armed with shotguns. Pumping bullets into two classmates they left one dead and the other fighting for his life. They went on the rampage through the school leaving in their wake a trail of bloody death and destruction. In the aftermath fifteen were dead, including the killers, and twenty-four were seriously injured. It is hard to understand why two 17-year-olds carried out this atrocious attack, but sadly, this urge to kill, whether meticulously planned or frighteningly spontaneous, cannot be predicted or prevented. On 5 November 2009, Nidal Malik Hasan was sitting at a desk at Fort Hood military base, just outside Killeen, Texas, awaiting a routine medical test. After a few uneventful seconds had passed, Hasan leapt out of his chair, produced two handguns and sprayed bullets around the room, killing thirteen people and injuring thirty. This attack lasted just ten minutes. SPREE KILLERS examines the events surrounding some of the world's most shocking mass killings; from the loner school kid with a shotgun to postal workers that made one too many deliveries.