Why Melbourne is new terror hot spot
It's perhaps not surprising that people who set out to kill and maim as many people in the name of a warped ideology would target Bourke St in Melbourne's frenetic heart.
After all, it ticks almost all the boxes of a terrorist's wish list - they can inflict as much damage to human life as possible and have the world's cameras watching them do it at the same time.
However, in the past two years, there have been three sickening mass attacks within the city's CBD while there have been none in Sydney since the 2014 Lindt siege - and there have been no similar incidents in other major Australian cities.
Hassan Khalif Shire Ali - a Muslim refugee from Somalia - crashed his car full of gas cylinders before stabbing three people, killing prominent Italian restaurateur Sisto Malaspina on Friday.
The first of the previous three incidents in Melbourne's CBD came in January last year, when four adults, a child and a baby died in a terrifying car rampage that also left dozens injured after James "Dimitrious" Gargasoulas allegedly ploughed his car through the busy pedestrian mall.
In September that year, a knife-wielding man also went on a rampage outside Flinders St station. He was tasered and arrested in dramatic scenes in Melbourne's CBD.
In December, there was another incident when Saeed Noori allegedly drove a car into people crossing the intersection of Flinders and Elizabeth streets.
At least 18 people, including a four-year-old boy and international tourists, were hit by the car that afternoon and one of them, 83-year-old grandfather Antonio Crocaris, died about eight days later.
So, how has Melbourne's CBD become a hot spot for this type of disturbing rampage?
Professor Clive Williams, a terrorism expert and visiting professor at the Australian National University, said "copycatting" could be a factor driving terrorists to hit the same spot agaian and again.
"The problem areas (in terms of terrorism) have often been the suburbs of both Sydney and Melbourne - but it has not manifested itself the same way in Sydney," he told news.com.au this morning.
"But then you tend to get the copycatting thing. This guy (Ali) might have seen what happened with the previous Bourke St thing and said, 'That was a good idea.' But it doesn't mean the attacks are linked in any other way though."
Prof Williams compared the inspiration for Friday's deadly attack to the recent spread of the needle contamination cases.
"You get one case and then you get umpteen cases of people copying it," he said. "I don't know why they do these things but I've seen it many, many times over the years - where people have copycatted things because they've believed it was an effective methodology.
"It's more likely to happen with individuals because with a group of people it tends to be more planned, more sophisticated and you have more chance of picking up on those operations.
"With the lone person, they're more likely to be impressed by other factors like copycatting, previous incidents and what people are telling them online are good ideas."
He added, terrorists on the extreme left, right and anarchist political movements are also influenced in the same way.
WHY THE CBD?
Despite a potential copycatting effect, Prof Williams said Melbourne's CBD has actually become a harder target for terrorists in recent years as security measures are stepped up.
"Downtown city areas are obviously desirable places (to strike) because you're going to get a lot of publicity and you've got the potential to kill a few people," he said. "But, it's become a harder target."
However, he said "lone actor" terrorists are notoriously hard to detect because there may not be any indicators.
"So the response is therefore preventive measures like concrete blocks to stop vehicles driving onto the sidewalk, loudspeaker systems so you can tell people where to go if something happens," he said. "You have police on hand so they can respond fairly quickly and contain the incident as quickly as possible."
He describes these as "after-the-event measures" which limit the amount of damage terrorists can cause.
"Obviously you want to anticipate things as much as you can, but the reality is there's a lot of people out there with mental issues and an awful lot of those could become violent and there's too many to keep on top of," he said.
He added that lone wolf attacks are far more complicated than people make out and are "inevitable" to some degree no matter how much money is spent on prevention.
"What's happened here and elsewhere is there's been a cut in funding for mental health and that's the big problem, because quite often lone actors aren't going to be inspired by Islamic State or whatever," he said. "It might just be a psychotic episode where they turn violent and they've seen this kind of attack works quite well so they go ahead and do it.
"The Prime Minister is trying to push this onto religious leaders, but that's not where the problem should sit. It should sit - in the case of lone actors at least - with mental health authorities."
However, he added the threat from IS as an entity is not over, despite the radical jihadist group losing much of its territory in Iraq and Syria.
"Islamic State still exists in the virtual world and they are still able to persuade people," he said. "It's out for revenge now and one of things they want revenge on is countries that were part of the US-led coalition and that never gets mentioned by politicians because it's an unpalatable truth."