Psychiatrists divide such mass killings into three broad categories; mass murders, "spree" killings and serial killings.
The tragedy of Dunblane last month was a mass killing, where the gunman Thomas Hamilton murdered all his victims in one place - a school gymnasium. However Michael Ryan's carnage in Hungerford in August 1987 would be categorised as a "spree", that is where the murders take place over a short period, but in separate locations. The Tasmanian shooting is most likely to be put under this heading.
Further study of such tragedies, notably those in the United States, have encouraged experts to sub-divide such events into three other groups according to the murderer. These are the "pseudo-commando"; the psychotic killer; and the "set and run" killer.
According to Dr Clive Meux, a consultant forensic psychiatrist at Broadmoor Hospital and a senior lecturer in forensic psychiatry at the Institute of Psychiatry in London, the pseudo-commando is generally a younger man, obsessed with fire arms. The psychotic killer, is generally severely mentally ill, though not invariably. Set and run killers are those who tend to plan the event meticulously.
In the Tasmania case, the limited evidence, of a confident young man with an apparent history of mental problems, indicates that he may be of the "psychotic" type. "He has been undertaking medical treatment for some problems that he has had," Tasmanian assistant police commissioner, Luppo Prinz, said yesterday.
Many experts agree that revenge is often the motivating factor for such killers. This revenge may result from a one-off event, for example losing a job or a partner, but more often these are simply spurs which push a deep-seated and long-held resentment to the surface, resulting in an explosion of violence.
Often there is a method in the gunman's violence, as he picks out those he deems suitable to die - maybe those based on a specific group they dislike, for example women, ethnic minorities or a profession.
In younger people the violence can erupt in those who have been over- protected in their youth and are perhaps teased about their perceived wimpishness. Forensic psychologist Ian Stephen, who advised on the ITV programme Cracker, said: "It could happen to kids who are over-protected and not allowed to express themselves. They harbour resentment for a long time while on the face of it they put up with being laughed at. Then they snap."
Susan Hope-Borland, who works with the North Wales Forensic Service, said: "Some are copycat crimes but others, like Hungerford are indiscriminate. Quite often, the kind of person who does these things has a grievance which is real or imagined."Reuse content