'The depravity of this incident is what has struck hardest': Peter Dutton overcome as he pays tribute to slain Australians

Anthony Albanese and Peter Dutton, a former Queensland police officer, were joined in a long line of stirring non-partisan tributes to officers Matthew Arnold and Rachel McCrow, and neighbour Alan Dare.

Along with the grieving, condolences and tributes also for the surviving officers Randall Kirk and Keely Brough, the Home Affairs Minister Clare O'Neil revealed that security agencies - and the parliament - are actively considering the implications of the apparent act of violent extremism.

The Opposition leader had to pause and contain himself as he spoke about the loss of "three wonderful Australians" in a "depraved" act.

"In this instance, what has hit hardest across the country is the execution style and the complete disregard for the human beings that these officers were," Mr Dutton told Parliament.

"The premeditated nature of the attack ... the callous lack of heeding the pleas that would have ... that would have echoed in between the gunshots."

The ambush killing of the three people and the deaths of three others at a remote property in Wieambilla have shocked the nation.

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Gareth and Stacey Train, the owners of the property, and Gareth's brother, former NSW school principal Nathaniel, were reportedly wearing camouflage during the assault, and were killed by police.

The Prime Minister described the killings as a "vicious and deadly atrocity that has stolen lives, broken hearts and shocked our nation".

They were also to him, "far beyond rational comprehension".

"Mr Speaker, we grieve for Alan Dare. And we grieve for Matthew Arnold and Rachel McCrow, who have paid a price that no one who puts on the uniform should ever have to pay. We can never count the true cost. We can never repay the full debt," Mr Albanese told Parliament.

"All we can offer is the humble thanks of a grateful nation and the heartfelt condolences of the Australian people."

The Home Affairs Minister noted the media reporting and speculation about the motivation behind these "despicable acts of violence", but indicated that immediate indicators are often incorrect.

Ms O'Neil said security agencies are actively considering the implications of online radicalisation, misinformation and extremism in the wake of the deadly attack.

"Once the picture does start to clarify, it is likely that radicalisation will form a part of it," she told Parliament.

"Radicalisation is not new, but it is absolutely clear from events here and around the world that conspiracy theories, disinformation and misinformation, problems as old as time are being turbocharged by technology into terrible acts of violence.

"They are presenting a new kind of threat to our national security. There will be deep and very important policy questions for us here as a parliament to think about how the country prevents and deals with violent extremism."

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