He's male. He tends to keep to himself. He's obsessed with vengeance and cannot express his emotion. That, psychiatrists say, is what makes a mass murderer.
But he said it was a myth that the mentally ill were more likely to kill.
"There is little evidence that schizophrenics are at a greater risk of causing violence," said Sydney University psychology professor Chris Tennant.
He said that only about 15 per cent of murders were committed by people with a diagnosable mental condition, but in a significant proportion of those cases the condition did not contribute to the violence.
"The link between psychiatric illness and violence is not a strong one, with the exception of depression causing suicide with guns," he said.
"If you look at the most recent mass homicides, such as Hoddle St and Queen St, in Victoria, and the Strathfield shootings, the person was not diagnosed as having a psychosis at all, they may well have had a serious personality disorder, may have been anti-social with a history of violence but not with a formal psychiatric diagnosis."
Dr Tennant said it was hard to predict violent tendencies among the mentally ill.
"The message arising from this is all about the availability of guns in society," he said.
"We can't easily predict violence. Both with ostensibly non-mentally ill people and with the mentally ill."
Experts distinguish between several types of killers. Those termed "mass murderers" kill a number of people in a given place at a certain time on a certain day.
Serial killers murder their victims over a longer period and in different locations.
But Bryant falls into another category: a mass murderer who kills over a relatively short period but in a number of locations.
An expert at the Institute of Psychiatry in London, Dr Clive Meux, said there were a number of classifications, such as "psuedo-commandos", who were obsessed with firearms, and "spree killers".
Experts said the wild gestures of these killers were often motivated by feelings of anger and vengeance and a desire to be respected.
These killers also engage in "copy cat" murders that are based on the deeds of other criminals. James Thompson, a co-director of the Traumatic Stress Clinic in London, said there was "a long learning component" in the behaviour of these killers.
"There is an established pattern of behaviour," he said.