A pair of junior Queensland police officers who survived a shooting ambush that claimed the lives of two fellow constables are grateful to be alive as investigators probe motives for the attack.

Constables Matthew Arnold, 26, and Rachel McCrow, 29, along with 58-year-old resident Alan Dare, were killed in a hail of bullets at a rural property at Wieambulla in the western Darling Downs region on Monday.

Constables Randall Kirk and Keeley Brough, both 28, escaped but the former was injured in the intense gunfire.

Constable Kirk, who is expecting his second child with wife Breanna next month, was due to be released from hospital on Wednesday after recovering from surgery to remove shrapnel.

The couple said they were overwhelmed by the messages of support from the public and “everyone from the Prime Minister down”.

“I’m feeling fine, just a little sore. My main thoughts are with the other police families at this awful time,” Constable Kirk said in a statement released by the police union.

“It means a lot to know the community cares for us all.”

Premier Annastacia Palaszczuk on Wednesday laid flowers at the Botanic Gardens Police Memorial in Brisbane to honour those killed in the attack.

“The constables were so young and brave, and Alan Dare, an innocent bystander,” Ms Palaszczuk tweeted.

“We want the Queensland Police family to know that we respect and appreciate what they do for us. If you see an officer, please offer them a kind word as they grieve the loss of their colleagues.”

Queensland Police Commissioner Katarina Carroll said constables Kirk and Brough were doing as well as could be expected and they were grateful to be alive.

“For them, it’s very difficult … they were there when their partners were killed,” Ms Carroll told ABC TV.

Their killers – former school principal Nathaniel Train, his brother Gareth and sister-in-law Stacey – died in a firefight with heavily armed tactical officers after the attack on the four officers.

Hundreds of rounds were exchanged before the trio were shot and killed.

All three members of the Train family were considered active shooters and died with their weapons clutched in their hands, a police source said.

One shooter was killed as he fired directly at the bulletproof windscreen of an armoured police vehicle as it approached the homestead.

Investigators are probing the motive for Monday’s attack, including whether the officers were lured to the property after following up on a NSW missing person report for Nathaniel Train.

They will also examine how the brothers were able to stockpile a cache of lethal weapons, including high-powered firearms, knives and axes.

The weapons had been legally obtained but were registered in NSW, a source said, prompting calls for changes to national gun registration.

Queensland Police Union head Ian Leavers called for weapon licensing protocols to be reviewed, including how the national database functioned when people crossed state lines.

Tributes at Chinchilla Police Station after two police officers were shot at a remote property. Photo: AAP

Reports the perpetrators were dressed in camouflage and whether the attack was premeditated will form part of the police investigation.

Investigators will also explore the killers’ motivations and possible extremist links after a series of posts under the name of Gareth Train were uncovered on conspiracy theory forums.

The posts include references to anti-vaccine sentiments and claims high-profile shootings were hoaxes or false flag operations.

The brothers’ father Ronald Train said Gareth had always been a volatile and overpowering person who was obsessed with weapons and guns.

The Train brothers cut ties with their parents 23 years ago but the retired pastor said he was still shocked the pair went down this violent path.

“They’ve been demonised by what’s occurred and I can completely understand that,” Mr Train told A Current Affair on Wednesday night.

“[They were] two boys who completely lost their way in life.”

-AAP