Police identify Westfield Bondi Junction attacker, here's what we know

A Queensland man who killed six people at a Sydney shopping centre had never been arrested or charged in his home state, police have confirmed.

Forty-year-old Joel Cauchi has been identified as the attacker who set upon people with a knife at Westfield Bondi Junction on Saturday afternoon.

Five victims - four women and a man - died at the shopping centre. Another woman, identified as Ashlee Good, died in hospital.

Cauchi, who grew up in Toowoomba, in Queensland's southeast, was shot dead by a senior officer at the scene.

Police had been with his family since Saturday evening. They have now released a statement, describing Joel Cauchi's actions as "truly horrific".

"We are absolutely devastated by the traumatic events that occurred in Sydney yesterday," his family said in a statement issued to the media via Queensland Police.

"Our thoughts and prayers are with the families and friends of the victims and those still undergoing treatment at this time.

"Joel's actions were truly horrific, and we are still trying to comprehend what has happened.

"He has battled with mental health issues since he was a teenager.

"We are in contact with both the New South Wales Police Force and Queensland Police Service and have no issues with the Police Officer who shot our son as she was only doing her job to protect others and we hope she is coping alright."

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Queensland Police Assistant Commissioner Roger Lowe said the family contacted authorities after seeing footage of the attack on TV.

Attacker grew up in Queensland

Cauchi lived on and off with his parents on a small residential street on Toowoomba's fringes.

For the past several years the 40-year-old was itinerant and had lived in his car and at backpacker hostels, Lowe said.

Cauchi was diagnosed with a mental illness at 17 and in recent years his mental health had declined, he added.

His family last heard from him in March, but their contact was periodic.

One neighbour, who did not want to be identified, told the ABC he "didn't mix with other kids when he was young".

Another neighbour told the ABC that he kept to himself.

"[His dad and I] had a yarn every now and then," he said.

The ABC understands the 40-year-old graduated with a diploma of arts from the University of Southern Queensland.

When contacted, a spokesman for the university declined to comment.

Killer 'acted alone'

In a statement, Queensland Health said Cauchi had been treated for mental health issues more than a decade ago, before his care was transferred to the private sector in 2012.

"Queensland Health extends our sympathies to everyone involved in the tragic incident in NSW," the statement said.

"We will work with Queensland and NSW police on any information and assistance we can provide."

Earlier, NSW Police Commissioner Karen Webb said Cauchi had "come to the notice of law enforcement" in NSW and Queensland for "mental health-related issues", but was not "known criminally".

Lowe said there was nothing to suggest the attack had any religious, political or ideological motive "that would contribute to an individual going into a crowded place and committing a crime of this nature".

"The information we have from the intelligence we have in Queensland... is that person involved in the horrific crime has acted alone and there is no ongoing threat to our community," Lowe said.

Police tracing movements

Cauchi had recently come to Sydney from Queensland, and had hired a "very small" storage facility which investigators had now accessed, NSW Assistant Commissioner Anthony Cooke said.

"We are continuing to work through the profiling of the offender but very clearly to us at this stage it would appear that this is related to the mental health of the individual involved," he said.

NSW Premier Chris Minns said Queensland Premier Steven Miles had "opened up all of the resources of the Queensland government for this investigation".

Assistant Commissioner Lowe said authorities were working closely with their interstate counterparts to share intelligence and assist with investigations.

"So that NSW Police can undertake their complex investigations into this event, certainly in preparation for a coronial brief for the NSW state coroner."

This story was first published by the ABC.