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Qld cop doubts foster father's confession

A foster father who murdered Gold Coast schoolgirl Tiahleigh Palmer claims he accidentally suffocated her when she tried to leave home after an argument.

But an experienced police detective says he struggles to believe the account provided by convicted sex offender Rick Thorburn, an inquest heard on Tuesday.

Thorburn is serving a life sentence for murdering Tiahleigh on October 29, 2015.

The 12-year-old's badly decomposed body - naked except for underpants - was found by fishermen six days later on the banks of the Pimpama River.

Thorburn sobbed while reading a one-page statement - he says was written about four years ago - in the Coroner's Court sitting in Brisbane on Tuesday.

But when questioned about the admission, further details and other allegations, Thorburn said he had no recollection.

"You can make up any story you like," he told counsel assisting the coroner Kate McMahon while threatening to leave the proceedings.

"I don't give a f***."

Asked when he dug up the statement, Thorburn said it was about a month ago when told he was to attend the inquest.

He had a handwritten original of the typed version handed into the inquest, but said he threw it away on the morning of Tuesday's proceedings.

Questioned why, he said: "This is the end of it. I don't need it anymore."

Thorburn said he had no recollection of being told by his wife Julene on the day Tiahleigh died that his son had had sex with the 12-year-old.

But Detective Senior Sergeant Chris Knight - who was involved in the investigation - believes Thorburn's account of accidentally killing Tiahleigh isn't consistent with information obtained by investigators.

"It doesn't sit well with me, what I heard earlier today, in terms of those circumstances," he told the inquest.

"I struggle to believe that."

Tiahleigh's family hope to get some answers from the two-day inquest before Deputy State Coroner Jane Bentley.

Despite internal reviews and criminal trials, no one knew what happened to Tiahleigh - who had been in the Thorburns' care for about 10 months - in her final moments, a pre-inquest hearing was told last month.

Although Thorburn pleaded guilty to her murder, he had never before given an account as to how he killed her.

In the hours before Tiahleigh died, she had been to a hip-hop dance class where she complained of stomach pains.

That day, son Trent Thorburn confessed to his mother that he'd had sex with the schoolgirl and feared the stomach pains were a sign she was pregnant.

From 8pm that night, Tiahleigh was home alone with her foster father for two hours.

She was never seen alive again.

Trent and brother Joshua Thorburn told the inquest they understood Tiahleigh was killed because of the sexual encounter.

Asked whether it was fair to say Thorburn killed the girl because he feared his son would go to jail, Trent Thorburn said he didn't remember his father saying that, but "that has just been my overall guess".

"He's my father and I believe that he would do anything to protect his family," Trent Thorburn added.

Julene Thorburn told the inquest her husband never discussed how he killed Tiahleigh.

"All he ever said to me was ... 'what you aren't told, you can't repeat', so he never told me anything around the circumstances of anything on the night," she said.

She said Rick Thorburn was concerned about their son going to jail, but when she returned home on the day Tiahleigh died her husband simply said the schoolgirl was no longer with the family.

Julene Thorburn said the process had been "long and drawn out" for her family, but she was prepared to answer any questions she could.

"There's not a day that goes by that I don't remember everything about having Tiahleigh with us," she said tearfully.

Members of the Thorburn family were convicted of being part of the crime - Rick Thorburn for the murder, Trent for incest, and Julene and Joshua for being part of an elaborate cover-up.

Rick Thorburn was sentenced to 20 years in jail.

Legal teams are expected to make submissions to Ms Bentley on the final day of the inquest on Wednesday.

© AAP 2021