Officers were following up an outstanding warrant relating to firearms and a border breach by shooter Nathaniel Train, as well as a missing person report, when they attended the Wieambilla property last week, Deputy Commissioner Tracy Linford said.
The warrant related to a border breach from December 2021 when Train illegally crossed the Queensland-NSW border gate in a 4WD carrying loaded guns and military knives.
Deputy Commissioner Linford said the wide-ranging investigation involved the counter terrorism command and other specialist police teams, but the shooting was not classed as "a domestic terror event".
"What we can see is a sentiment displayed by the three individuals … that appears anti-government, anti-police, conspiracy theorist type," she said.
"We can't see them connected to any particular group that they might have been working with, or inspire them to do anything. We haven't located anything like that at this point in time."
She said security and counter terrorism teams were working to determine possible motivations for the attack, including "religiously-motivated extremism" and "pathological-fuelled violence".
Police attended property multiple times
Deputy Commissioner Linford said police had gone to the property multiple times to locate Train to question him about the border breach and firearms that were dumped at the time.
"[He] had driven his vehicle through an e-gate, causing damage and his vehicle got bogged at that location," she said.
"When police subsequently investigated the vehicle because they were speaking to other locals in the area, two firearms were handed in.
"Those firearms were registered to Nathaniel Train. He was a firearms licence holder."
However, Deputy Commissioner Linford said Nathaniel Train's firearms licence had been suspended.
"It was suspended as a result of the two firearms being left at the border," she said.
"Police wanted to speak to Nathaniel about the events of the December incident and had gone to the property but were unable to raise any individual there.
"They had left messages at the property, both by card and at least five messages as well, but they had not had any response."
'Run-of-the-mill job'
Deputy Commissioner Linford said it was normal for police to visit the property of family members when following up a missing person report.
"This was a run-of-the-mill policing job. There wasn't anything to flag particular concern with our members who were attending the scene that day.
"His brother and sister-in-law, who was previously actually his wife, did reside at the address," she said.
"So that is a normal course of action for police to check with relatives of a missing person to see."
She said Nathaniel Train's wife, who resides in NSW, reported him missing as she had not physically seen him in 12 months.
Asked if the missing person's report could have been premeditated, Deputy Commissioner Linford said police believed his wife's report was genuine.
Deputy Commissioner Linford said six weapons had been seized from the property during the police crime scene search, along with three bow and arrows and three knives.
"Two of those [guns] were weapons that were registered to Nathaniel Train, three of those were unregistered," she said.
"One of those [firearms] we are following up lines of inquiry to find out who the owner of that particular firearm is."
Little known about Train family
Deputy Commissioner Linford said police had very little information about the Train family prior to the shooting incident.
"Nathaniel Train's only history with us was a 2014 driving offence," she said.
Deputy Commissioner Linford said Gareth Train had a 1998 offence for unlawful possession of a firearm, which had expired.
"In terms of Stacey Train, we have no criminal history, or intelligence holdings on her," she said.
"So, you can see from that, we knew very little about the Trains and there was nothing that would have caused that particular flag for our members who attended."
Deputy Commissioner Linford said police had been in contact with law enforcement agencies across the country and overseas.
"We are doing a social media trawl and looking for any evidence of postings and also any evidence of people they were connected to," she said.
Deputy Commissioner Linford said the "multidisciplinary" investigation was being led by the Ethical Standards Command.
She said other specialist police teams were involved in the investigation include the homicide team, local police and intelligence command.
Palaszczuk to raise national gun register with other leaders
Premier Annastacia Palaszczuk said she will raise the establishment of a national gun register when national cabinet meets next year.
"What we want to see is that if a person is registered for guns in one state they are also recognised in the other state, if they transfer, that's the issue we need to look at," she said.
The premier said the state government was "always looking at how we can tighten" firearms regulations.
The government will contribute $100,000 towards the Queensland Police Union's remembrance fund for constables Matthew Arnold and Rachel McCrow, who were killed by the Trains.
Ms Palaszczuk said the money would support their families.
