Coroner Terry Ryan resumed the Wieambilla shootings inquest in Brisbane on Wednesday after a seven-day break without hearings.
Brothers Nathaniel, 46, and Gareth Train, 47, used high-powered rifles during an ambush to kill Constables Matthew Arnold, 26, and Rachel McCrow, 29, at a remote property west of Brisbane, late in the afternoon of December 12, 2022.
High-powered rifles were used to kill two police constables at a rural property in Wieambilla. (HANDOUT/CORONERS COURT OF QUEENSLAND/QUEENSLAND POLICE SERVICE)
Queensland Police Deputy Commissioner Cheryl Scanlon testified that a person in the United States was part of an ongoing investigation.
"We have a current and open terrorism investigation that is not yet complete. There is another individual ... a very close associate of the Trains ... It's an open matter here in Queensland," she said.
Arizona man Donald Day Jr was arrested by FBI agents in December 2023 and charged with making threats and illegal firearms possession in the US.
Day allegedly sent messages about a "Christian end-of-days ideology" known as premillennialism to the Trains between May 2021 and December 2022.
Day entered pleas of not guilty to all charges in the Arizona District Court in May 2024.
Nathaniel Train joined Gareth and his sibling's wife Stacey, 45, to fatally shoot neighbour Alan Dare, 58, soon after killing the two constables.
All three Trains were shot dead by specialist police officers hours later after they refused to negotiate or surrender.
Police receive 340 new firearms licence applications a week, Inspector Cameron Barwick testified. (Darren England/AAP PHOTOS)
Mr Ryan previously heard the Trains possessed both registered and unregistered firearms, including an illegally shortened rifle and shotgun.
Nathaniel Train's Queensland firearms licence had been revoked due to him dumping several weapons while crossing the NSW border.
Queensland Police weapons licensing group Inspector Cameron Barwick testified that mental health checks for firearms licence applicants would be "favourable" compared to "subjective" scrutiny by police officers.
Mr Ryan heard there were "just shy of 225,000" firearms licences in Queensland and police received 340 new applications a week.
Queensland Police would have to "uplift" to achieve real-time information-sharing under a national firearms register by July 2028, Insp Barwick said.
"Our system still has a lot of manual processing ... We will have to move to a web-based system," he said.
Constables Arnold and McCrow were not wearing bullet-resistant vests at the time, and had yet to be issued with new police integrated load-bearing vests that can be fitted with soft armour ballistic panels.
Soft armour was unlikely to have saved one officer killed, Det Insp Jason Hindmarsh said. (Darren England/AAP PHOTOS)
Ethical standards command Detective Inspector Jason Hindmarsh, the senior officer who investigated the shootings, was asked if Const Arnold, the first person to be shot, would have survived if he wore soft armour panels.
"I can't say. Soft armour is not designed to withstand (the calibre of bullet used)," Insp Hindmarsh said.
Mr Ryan previously heard evidence that Nathaniel Train hid in a concealed sniper's position and used a rifle to open fire on Const Arnold with large military-calibre bullets.
Insp Hindmarsh said hard armour panels, intended for situations needing greater protection from firearms and edged weapons, were also not designed to stop high-powered rifle bullets.
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