Now disturbing new details have emerged of exactly how Thorburn killed his 12-year-old foster daughter and his family helped cover it up for 11 months.
According to a statement by police in 2016 obtained by ABC, Thorburn’s wife Julene Thorburn, watched her husband from their kitchen window as he loaded Tiahleigh’s lifeless body into his blue Ford Falcon. Palm trees outside their Chambers Flat home in Brisbane’s south blocked her view, but she reportedly knew what was going on.
Thorburn had reportedly ordered his two teenage sons, Joshua and Trent to leave the house and go somewhere they could be seen by other people.
"It's all taken care of," Rick Thorburn reportedly told his family.
“Don’t ask any questions … try to be normal — the less you know, the better,” Rick reportedly told his family, according to Julene’s statement.
Six days later, Tiahleigh’s body was found on the banks of the Pimpama River, so decomposed a cause of death was unable to be determined.
Rick and Julene had been worried their son Trent would go to jail after revealing he had a sexual relationship with the 12-year-old and feared that she was pregnant.
On last night’s 60 Minutes, secret police recordings revealed how the parents coached their sons to lie and cover up the crime.
“We have to stick to the same story about her going to school the next day and whatever,” Julene can be heard saying in the police recording.
“She came into your room, you remember waking up, you were still drunk, you were still ... whatever,” Rick Thorburn tells his son.
The family unit however were divided, with wife Julene and eldest son Joshua discussing “coming clean”.
“If we have to come clean that’s just between you and I,” Julene said. “Dad made the decision to go down that path unfortunately.”
Despite this, the family carried on the lie for 11 months before an anonymous phone call tipped off police to revisit the family as suspects.
“An anonymous call came through,” Detective Hansen told reporter Tara Brown.
“There was a Facebook message sent from Trent outlining a sexual activity with Tiahleigh, and that there’d been a family meeting the night before she disappeared.”
Trent wrote how he wanted Tiahleigh “out of his life”, but referred to her as a “source of income” for his parents.
“You look at the content of that Facebook message, you look at the fact there’s a family meeting and just by coincidence she goes missing the next day,” Detective Hansen said.
Detective Hansen described this as the turning point in the investigation, and ultimately led Julene and Joshua to come clean and reveal exactly what happened on the night of Tiahleigh’s murder.
“(She was) in her bedroom, sitting on her bed,” Julene says on the police tape. “I said goodnight to her there and expressed to her that she needed to stay there and put herself to sleep.”
Julene and her sons then left Tiahleigh home alone with Rick, returning three hours later to be told by Rick, “Tiah is no longer with us”.
Last week Rick Thorburn was sentenced to life in prison and will be eligible for parole in 2036.
Julene and Josh Thorburn were charged with perjury and attempting to pervert the course of justice.
Trent Thorburn was charged with incest, attempting to pervert the course of justice and two counts of perjury.
Julene, Josh and Trent have all since been released from jail.
During the 60 minutes special, Tiahleigh’s biological mother Cyndi Palmer gave her first interview since the sentencing of Rick Thorburn, firing back at critics who said she was to blame for her daughter’s death.
“I didn’t murder my daughter,” she said. “I did everything I could to try and get her back. I wanted our family to be whole again.”
Ms Palmer revealed her reservations of Rick Thorburn, and said Tiahleigh had feared being left alone with the foster father.
“She didn't want to be left alone with [Rick],” Ms Palmer revealed. “And she started misbehaving, she was running away, she didn't want any bar of Rick.
Tiahleigh had been in foster care since the age of seven after Ms Palmer says she feared for her life in a "domestic violence situation", and came to live with the Thorburns in January 2015.
“People blamed me for her death.. I try not to let it bother me. But I guess maybe it is a little bit of guilt because obviously I was meant to be a mother and I should have made better choices.
“But I didn’t murder my daughter.”