"Lone wolf" terrorists each have their own modi operandi, but many could be stopped if more attention is paid to some of the common traits they tend to exhibit, say security experts reacting to the siege in Sydney which left three dead, including the gunman.
Man Haron Monis, 50, an Iranian refugee and self-styled Muslim cleric, has been categorised by reports as a "lone wolf" terrorist - one who acts without connection to or aid from a terrorist group.
With such one-man attacks on the rise, questions surrounding these lone operators and the challenge of identifying them before they commit violent acts have once again come to the fore.
While these attackers come from a wide range of backgrounds and social classes, they do have commonalities, according to criminology professor Mark Hamm from Indiana State University.
Prof Hamm, who has studied 98 cases of "lone wolf" attacks in the United States since the 1940s, said: "Unlike terrorists who belong to organisations, they have personal frustrations mixed with their political grievances."
Personal problems could include health, family or social issues that the attacker is grappling with.
Monis had a long list of run-ins with the law. The most recent included being charged with more than 40 counts of sexual assault this year; last year, he was charged with being an accessory to the murder of his former wife.
Mr Edward Turzanski, senior fellow at the Foreign Policy Research Institute and the co-chair of its Centre for the Study of Terrorism, said: "In many instances like this, it is not such a huge surprise that he could commit an act of violence."
While it is hard to pinpoint a definitive profile that fits a "lone wolf" terrorist, Mr Turzanski said they are "quite frequently the quiet, introverted type who find meaning and fellowship being part of a cause".
Because of this, they have an affinity with other sympathisers and connect with them online through chat groups or social media, say security experts.
While some say "lone wolves" are difficult to pick out because they operate in social isolation, Prof Hamm believes there have been many missed opportunities in identifying these individuals and preventing violent acts. "Eighty per cent of cases do broadcast their intent to commit terrorism in the form of a statement to family and friends or on social media," he said.
For instance, Zale Thompson, a Muslim convert who attacked four New York City policemen with a hatchet in October, had made various posts on social media sites advocating "jihad" and guerilla warfare against the US.
Said Prof Hamm: "The point is that they are not in total isolation... We often see one signalling event after another."
So, if it is possible to spot these lone terrorists, why isn't more being done to stop them?
Mr Turzanski said that while potential terrorists often do turn up on the radar of law enforcement, there is often the "concern of racial profiling", which puts law enforcement in a bind.
Some countries have tightened legislation to protect their citizens. This year, Australia passed laws to ban citizens from going overseas to fight alongside terrorist groups and has made it an offence to advocate terrorism.
Yet, this did not prevent Monday's siege, a sure sign that legislation alone is not enough. Experts say the community also needs to be vigilant in identifying and reporting potential terror threats.
"That is very difficult because people feel ethnic kinship or sometimes they are blood relatives," Mr Turzanski said. "But the best way to deal with this is for communities to start reporting on those who are openly engaged in acts that are leading up to violent attacks."
This article was first published on Dec 18, 2014.
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