The opposition leader called for tightened regulation on encrypted messaging services that would allow conspiracy theories to be shared, saying law enforcement mustn't be prevented from viewing that dangerous content.
Three members of the Train family - former school principal Nathaniel Train, his brother Gareth and sister-in-law Stacey - killed two police officers and 58-year-old neighbour Alan Dare at a rural property in the western Darling Downs.
Gareth Train subscribed to a number of conspiracy theories including the 1996 Port Arthur massacre being a false-flag operation, although he posted about them on an online forum rather than via encrypted software.
Mr Dutton said the anti-government rhetoric being shared should concern any "right-thinking Australian".
"We've seen in recent years the spread of disinformation on the internet and the way in which that infects people's minds and changes their whole persona, their whole perspective and causes them to commit … extreme acts," he told reporters.
"You worry about the information your children are accessing online … they can be encouraged to spread all sorts of conspiracy theories and subscribe to those and spread that hatred and we should be very concerned about that."
The opposition leader said he'd back any measures to hold those behind encrypted messages to account.
"Police agencies and intelligence agencies … just can't get access (encrypted messages), as they normally would," he said.
"When you've got that environment where there can be no transparency and there can be no discovery, then you will have these groups manifesting their lunacy and reinforcing each other's ideas and prejudices and it manifests in tragic ways."
Federal parliament will hear speeches on Thursday in relation to the bravery of the police officers and neighbour.
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