Inquest told Tiahleigh Palmer was likely sexually abused by foster dad Rick Thorburn

Tiahleigh Palmer before she was murdered by her foster dad. Photo / Supplied

Warning: This article deals with sexual abuse. Helplines can be found at the bottom of the page.

Murdered Queensland schoolgirl Tiahleigh Palmer was not only sexually abused by her foster brother, but was likely also abused by her foster dad, an inquest has been told.

Rick Thorburn – who was jailed for life in 2018 for murdering Tiahleigh – stunned the inquest on Tuesday when he tearfully claimed he may have accidentally smothered the 12-year-old in October 2015 during an argument.

Tiahleigh's body was dumped by her foster father. Photo / Supplied

Tiahleigh was placed into foster care alongside her siblings after her Kiwi mum Cyndi Palmer went to authorities with fears for her children's future due to a severe domestic violence situation she was in.

Tiahleigh's mother later spiralled into drug addiction and homelessness as the reality of life without her children set in.

Cyndi Palmer says she put her children into foster care when she was suffering domestic violence. Photo / File

As the inquest wrapped up on Wednesday, counsel assisting the coroner Kate McMahon explosively told the court it could be inferred that Thorburn sexually abused Tiahleigh and her murder could have been to cover up not only step brother Trent's actions, but his own.

The foster father was not in court as he was blasted as "remorseless" and "self-serving".

"That is an inference available on circumstantial evidence," McMahon said.

She said Thorburn had not denied he may have had sexual contact with the girl and he had previous convictions for child sex offences.

The Thorburn family, left to right, Rick, Josh, Julene and Trent, pictured in 2014. Photo / Facebook

McMahon said there was some evidence in Thorburn having a "sexual interest" in Tiahleigh and he had made statements about a sexual act involving the young girl.

"If there is evidence [Thorburn] was acting potentially to cover up not only Trent's sexual contact with Tiahleigh but his own possible [encounter], that is further reason to reject his account," she said.

The two-day inquest has been rocked by evidence from Thorburn, who spoke for the first time about what he says happened the night he killed her.

Thorburn claimed Tiahleigh had packed a bag and was leaving down the driveway when she began screaming and swearing at him.

The inquest into Tiahleigh Palmer's death is examining how the 12-year-old died at the hands of her foster father Rick Thorburn and how he disposed of her body. Photo / Supplied

He said he grabbed her around the waist and put his hand over her mouth as he dragged her back to the house.

He said by the time he arrived on the veranda, she was not responding.

McMahon told the court it could be inferred Tiahleigh died of asphyxiation, either suffocation or strangling, between 7pm and 10pm on October 29, 2015.

McMahon said a recorded prison phone call between Thorburn and his wife suggested a deliberate plan to claim a lack of memory in order to frustrate the inquest.

"Even now he is remorseless for this murder," McMahon said.

Tiahleigh Palmer before she was murdered by her foster dad. Photo / Supplied

"That remorselessness has also been evident in his behaviour towards this inquest."

Thorburn's defence barrister Matthew Hickey said the court had no reason to doubt the truthfulness of his client's memory loss.

He called the claims of evidence about his client's sexual abuse circumstantial and arising from hearsay.

"It's an inadequate basis for a finding that there's an inference of sexual abuse against a child in his care," Hickey said.

"It rises no higher than a possibility, not even a probability and certainly not the most probable outcome.

He argued his client was remorseful as he had shown genuine sorrow when he took the witness stand and gave his statement.

"There's no evidence to suggest Tiahleigh was strangled … the only evidence is that she was smothered," Hickey said.

Detective Inspector Chris Knight, who was the operations leader in the homicide investigation, told the court on Tuesday he had trouble accepting Thorburn's confession.

He said the attempt to leave did not add up with the girl's past history, as he was not aware of any instances where she attempted to leave home.

"My opinion is that … I don't believe the account provided is consistent with the known information," he said.

Inspector Knight said he believed Tiahleigh's body was stored in the back shed of the Thorburns' property and was moved after she was reported missing on October 30.

He said he believed the body was disposed of that evening.

Tiahleigh's death shocked the nation when her body was found on the banks of the Pimpama River in November 2015.

Her body was so badly decomposed a cause of death could not be determined.

She was last seen alive on October 29, 2015 attending a dance class, where she complained of stomach pains.

Trent Thorburn, the foster brother of murdered 12-year-old schoolgirl Tiahleigh Palmer, leaves court. Photo / NCA Newswire

That same night, Trent told his mother he'd had sex with Tiahleigh and was concerned she was pregnant.

The foster parents feared the young girl's stomach pains were consistent with pregnancy and were concerned their son could go to jail.

The inquest also heard from Thorburn's wife, Julene, who said she still visited him behind bars and remained married to him.

She said Thorburn never told her what happened the night Tiahleigh was murdered but gave an ominous message: "What you aren't told, you can't repeat."

Julene bizarrely changed into new clothes and concealed herself with a wig to avoid waiting media outside after giving evidence.

Each of the Thorburns have received jail terms relating to Tiahleigh's death.

Trent was jailed for four years for having sex with Tiahleigh but was released on parole in 2018 after 16 months behind bars.

Julene was sentenced to 18 months' jail for perjury and attempting to pervert the course of justice, with the sentence suspended after six months.

Deputy State Coroner Jane Bentley is expected to deliver her findings in the coming weeks.

Where to get help:

• If it's an emergency and you feel that you or someone else is at risk, call 111.
• If you've ever experienced sexual assault or abuse and need to talk to someone call the confidential crisis helpline Safe to Talk on: 0800 044 334 or text 4334. (available 24/7)
• Male Survivors Aotearoa offers a range of confidential support at centres across New Zealand - find your closest one here.
• Mosaic - Tiaki Tangata: 0800 94 22 94 (available 11am - 8pm)
• If you have been abused, remember it's not your fault.