First, there was the deadly nightclub attack by a lone gunman in the Florida city of Orlando, in the United States.
Then crowds watching fireworks in the French Mediterranean city of Nice were run over and gunned down by a man in a van.
After those mass killings, a teenager armed with an axe and a knife attacked passengers on a train in the German city of Wurzberg.
In just two months, the world has witnessed a series of attacks on so-called soft targets by lone individuals, or "lone-wolf" attackers.
Such individuals often operate free from the notice of authorities because they do not follow a chain of command.
Research shows they may be emotionally or mentally unstable and are more likely to be rapidly attracted to militant groups like the self-proclaimed Islamic State.
Now, Prime Minister Malcolm Turnbull has asked Australia's counter-terrorism coordinator, Greg Moriarty, to investigate the risk of it happening in Australia.
Mr Moriarty says the review will consider a broad range of issues.
"Why are people attracted to this ideology, and what we can do to try and help them, divert them from a path of heading towards violent extremism? And the Prime Minister has made it clear to me that he sees this as a very multidimensional problem, as one that will take many years, and perhaps decades."
The review could lead to greater cooperation between the national-security and health sectors.
Malcolm Turnbull has told radio 3AW that will all be part of the review.
(Turnbull:) "What I want to do is make sure Australians are kept safe."
(Interviewer:) "So how do you do that? Do you need access to the mental-health files?"
(Turnbull:) "Well, this is why Greg Moriarty is going to undertake this review, with, obviously, state and territory police."
While privacy remains a concern, some national-security specialists say more collaboration is needed to spot early warning signs.
The Australian National University's Leah Farrall says it could make a difference.
"There are, often, indicators that are missed. Family members can miss indicators, community members can miss indicators, and, after any form of crime, it can become apparent to people that there were indicators. So we really need to get across that a little better and step back, I think, from some of the politicking and look at better resourcing of investigations focused on these types of things."
Lindt Cafe gunman Man Haron Monis had a series of criminal and mental-health issues leading up to the 2014 Sydney siege.
British policy experts who have reviewed the New South Wales police response to that siege will continue to give evidence at an inquest next week.
The coroner is due to hand down his findings later this year, and part of that will include determining whether Monis's actions could have been prevented.
Mr Moriarty says it is important his agency continues to adapt as new terrorism tactics emerge.
"When we have a very strong terrorist risk in this country -- the threat level is at 'probable' -- just to make sure that all of those procedures are appropriate for the current circumstances that we find ourselves in."
