A coroner has rejected Rick Thorburn's claim that he killed Tiahleigh Palmer accidentally.
Queensland schoolgirl Tiahleigh Palmer likely died as a result of choking or asphyxiation in a deliberate act by her remorseless 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 730 and 930pm on the 29th of October 2015," she said, handing down her findings in Brisbane on Friday.
Thorburn sobbed while reading a one-page statement - he says was written about four years ago - in the Coroners 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, Thorburn answered: "I don't know".
His lack of memory was also rejected by Ms Bentley who said it was inconsistent with a phone call made to his wife before his appearance at the inquest, as well as opinions of prison psychologists.
"Rather, they are evidence of his intention to mislead the inquest and take to his grave the circumstances of Tiahleigh's death and his disposal of her body," she wrote in her findings.
"I find that Mr Thorburn is completely without remorse for any of his offending.
"In fact, when one listens to the phone discussions between him and his wife, it is clear that he perceives himself as being unfairly dealt with and victimised by the media and public opinion, as does Ms Thorburn."
While the exact cause of death could not be determined, Ms Bentley said Tiahleigh was most likely choked or asphyxiated - taking into account a lack of injuries to her body and no evidence of blood at the Thorburns' house.
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.
In the hours before she 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 that he had sex with the schoolgirl and feared the stomach pains were a sign she was pregnant.
Thornburn 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 Rick Thorburn for two hours.
She was never seen alive again.
Another possibility was Rick Thornburn himself was having a sexual relationship with his foster daughter.
"In considering this possibility I note that Richard Thorburn had a predilection for young girls. He pleaded guilty to sexual offending against a four-year-old and an 11-year-old who were in his wife's care at the same time Tiahleigh was living at his house," Ms Bentley said.
However, she agreed with submissions from Thorburn's lawyer that that circumstantial evidence was insufficient, and the most likely motivation was to protect Trent.
Numerous reviews were conducted into the involvement of government agencies with Tiahleigh, and the coroner made no further recommendations.
He 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 - 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 and Ms Bentley said his lack of remorse and failure to co-operate with the inquest should be considered if he applies for parole.
Australian Associated Press