Examination of nine cases of mass murder from around the world, including Australia and New Zealand. Attempts to find reasons why a person becomes a mass murderer, and to detect a pattern in the phenomenon of mass murder. Posits that there are shared traits in the nine men examined that are powerful predictors of their behaviour. Includes illustrations and glossary. The New Zealand author was a police officer for over 35 years, has been involved in numerous murder investigations and has studied criminology and criminal law. His previous books are 'Twenty-two Hours of Terror' and 'Shattered Dreams'.