Convicted sex offender Rick Thorburn is serving a life sentence for the murder of the 12-year-old on October 29, 2015.

Circumstantial evidence, including previous sexual offending and alleged comments made by Thorburn about his foster daughter, gave rise to the possibility, the court was told.

However, his lawyer Matthew Hickey said it was unnecessary to "venture into that particular territory" given the evidence permits "nothing more than a possibility".

Mr Hickey said there was also no evidence Tiahleigh was strangled, only that she was smothered, and rejected suggestions Thorburn was remorseless.

"The man sat in the box, he cried when explaining the sorrow that he felt about the thing that he quite candidly conceded he had done, he pleaded guilty to the crime," he said on Wednesday.

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.

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.

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 that he'd 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.

Tiahleigh's body - naked except for underpants - was badly decomposed when found by three fishermen on the banks of the Pimpama River on November 5, 2015.

Authorities haven't been able to determine how she died.

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.

Inquest findings are expected to be handed down next week.

Australian Associated Press