Queensland schoolgirl Tiahleigh Palmer likely died as a result of choking or asphyxiation in a deliberate act by her foster father, a coroner has found.
Convicted sex offender Rick Thorburn told the inquest into Tiahleigh's death he accidentally suffocated his foster daughter, but this was rejected by Deputy State Coroner Jane Bentley.
"I find that Richard Thorburn deliberately killed Tiahleigh, he did so at the residence of the Thorburn family between 7.30 and 9.30pm on the 29th of October 2015," she said, handing down her findings in Brisbane on Friday.
While the exact cause of death could not be conclusively determined, Ms Bentley said Tiahleigh was most likely choked or asphyxiated.
Thorburn sobbed while reading a one-page statement – he says was written about four years ago – in the Coroner's Court last week.
He said he had no recollection of being told by his wife on the day Tiahleigh died that his son had had sex with the 12-year-old.
Asked whether there may be a link between the circumstances of him killing Tiahleigh and finding out about the sexual relationship, he answered: "I don't know".
He also told the inquest he was "coerced into pleading guilty" earlier to multiple charges of sexual assault for offences unrelated to Tiahleigh.
Despite internal reviews and criminal trials, no one knows what happened to Tiahleigh in her final moments, a pre-inquest hearing was told last month.
"(Thorburn) has pleaded guilty to her murder but has never given an account, either on oath or otherwise, as to how he killed her," counsel assisting the coroner Kate McMahon said during the hearing.
Foster brother confessed to having sex with Tiahleigh Palmer
In the hours before Tiahleigh died, she had been to a hip-hop dance class where she complained of stomach pains.
That same night, Thorburn's son Trent confessed to his mother, Julene, he'd had sex with the schoolgirl and feared the stomach pains were a sign she was pregnant.
Thorburn and his wife feared a pregnancy could mean Trent would go to jail, according to earlier proceedings.
That night, Julene, Trent and brother Joshua went out, leaving Tiahleigh home alone with Thorburn for two hours.
She was never seen alive again.
Tiahleigh's body – naked except for underpants – was badly decomposed when found by three fishermen on the banks of the Pimpama River near the Gold Coast on November 5, 2015.
Members of the Thorburn family were convicted of being part of the crime – Thorburn for the murder, Trent for incest, and Julene and Joshua for being part of an elaborate cover-up.
Thorburn was sentenced to 20 years in jail.
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