Tiahleigh Palmer's foster Rick Thorburn allegedly told his family "it's all taken care of" and begged them not to ask questions when the schoolgirl disappeared, court documents show.
Mr Thorburn, 56, is in custody on a murder charge following the finding of the 12-year-old's body in the Pimpama River six days after she vanished last October.
Documents filed in the Brisbane Supreme Court this week contain allegations about his behaviour as relayed to police by his wife Julene, 54.
Mrs Thorburn last month pleaded guilty to perjury and attempting to pervert the course of justice.
She told police her husband was concerned about the fate of his son Trent, 19, after revelations he allegedly had an incestuous relationship with the foster child.
Mrs Thorburn said she left to go to her sister's house one night in late October 2015 while her husband was alone at home with Tia.
Later, he sat the family down and Mrs Thorburn asked if Tia was OK.
"Rick said, 'It's all taken care of'," she said.
"Rick said 'don't ask any question, you don't need to know. I have taken care of it'."
Mrs Thorburn alleges he later warned her not to go in Tia's bedroom and to "shut up, don't question it".
The next day, she said Mr Thorburn told their sons to "make sure you are accounted for" and that he would be leaving his phone at home and going out.
He also told her "do not ask any questions" and to "stay away".
"My gut feeling is that Rick meant he had to dispose of Tia's body," Mrs Thorburn told police.
When she asked where he went, Mr Thorburn allegedly replied: "the less you know the better".
A police statement by Mrs Thorburn's mother Dorothy Fayle, 77, also reveals tensions within the family.
"Julene said, 'I do not feel like Rick is my husband, it's hard to relate to him and treat him how I have always done'," Mrs Fayle told police.
Mrs Fayle said she also asked the Thorburns' other son, Joshua, how he felt about his father.
"Josh said, 'He is my dad but from that night on I can't relate to him as my dad'," she said.
AAP