As the number of serial killers worldwide has risen steadily - from the emergence of Jack the Ripper in 1888 to Harold Shipman and Ivan Milat, the backpacker killer of the Australian outback - the need to understand mass murder is becoming more urgent.

As the number of serial killers worldwide has risen steadily - from the emergence of Jack the Ripper in 1888 to Harold Shipman and Ivan Milat, the backpacker killer of the Australian outback - the need to understand mass murder is becoming more urgent.