Members of the Train family - former school principal Nathaniel Train, his brother Gareth and sister-in-law Stacey - gunned down two officers who'd attended their property to investigate a missing person report on Monday.
Constables Matthew Arnold and Rachel McCrow were killed along with neighbour Alan Dare, who was shot in the back when he attended the property to assist.
The officers will have their names added to the National Police Memorial in Canberra in time for next September's Police Remembrance Day.
Police are looking into the Train brothers' online activities, including their possible involvement in extremist conspiracy groups and forums.
The opposition leader said friends and families of people falling down conspiratorial rabbit holes must proactively contact authorities before tragedy strikes.
"There are some sick individuals out there and the internet's made it possible for them to spread their lies and their hatred, and so it is difficult for authorities to pick that up," Mr Dutton told Nine Radio.
"The parallel obviously is with young people who are being indoctrinated online, with an ISIL ideology, just a hatred of authority … they spend hours and hours and hours reading this information and information is deliberately posted, knowing that will influence people in a negative way."
Mr Dutton doubled down in his criticism of encrypted messaging services, although the Train family posted in forums rather than via the secure software.
Home Affairs Minister Clare O'Neil said security agencies were "actively considering" the implications for national security after initial reports of the perpetrator's online radicalisation and violent extremism emerged.
"It's really important that we let law enforcement and national security agencies do their job (but) once the picture does start to clarify, it is likely that radicalisation will form a part of it," she told parliament on Thursday.
"It is absolutely clear ... that conspiracy theories, disinformation and misinformation ... are being turbocharged by technology into terrible acts of violence."
Ms O'Neil said online radicalisation was a new kind of security threat and parliament would have to consider deep and important policy questions to address how Australia prevented such crimes.
Early Childhood Education Minister Anne Aly - who worked as an academic in counter terrorism and countering violent extremism before she entered politics - said the perpetrators appeared to have been on a trajectory to violent acts.
"We have to get better at recognising those warning signs, we have to get better at intervening early, we have to get better at early identification."
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