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.
Prime Minister Anthony Albanese, who said the officers paid a price no one who puts on the uniform should ever pay, will lead tributes to the pair in federal parliament on Thursday.
Constables Randall Kirk and Keeley Brough, both 28, narrowly escaped but the former was injured in the intense gunfire.
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.
Police determined to identify the motive for the lethal attack will trace the brothers' online activities, delving into extremist and fundamental communities online.
"We'll investigate their families, their friends, everything they've done in the last six months to a year," Queensland Police Commissioner Katarina Carroll said.
"We will get to the bottom of this because we need to know what happened and why."
The Train brothers' father Ronald Train said he was struggling to comprehend how his sons could be responsible for the murderous attack.
"I just could not understand how something like this could have occurred, with two children who had been raised by my late wife Gwen and myself," the retired pastor told A Current Affair on Wednesday.
"They went down this track, this dark track, which we have no understanding of."
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