Foster Father Sentenced To Life In Prison For Tiahleigh Palmer Murder

57-year-old Rick Thorburn admitted to murdering the 12-year-old schoolgirl in 2015

Tiahleigh Palmer's foster father Rick Thorburn has been sentenced to life in prison after pleading guilty to her murder.

Rick Thorburn pleaded guilty on Friday to murdering 12-year-old Tiahleigh Palmer after discovering his son Trent had sex with the underage girl.

Her body was found on the banks of the Pimpana River on the Gold Coast in November 2015, six days after she disappeared.

Justice David Boddice described Thorburn's actions as "cold, calculating, and callous".

Last year, Thorburn's wife and two sons were also jailed for lying to detectives about Tiahleigh's death.

In handing down sentence in Brisbane Supreme Court on Friday, Justice David Boddice described Thorburn's actions as despicable.

"You murdered this defenceless child who relied on you for protection," he said.

"Your offending involves truly appalling conduct."

After Thorburn killed Tiahleigh, he insisted to his family that they had to protect Trent and all make the same lie to detectives.

They lived their lives normally the next day, and their story would be that Tiahleigh had vanished after leaving for school.

When she was reported missing from school Thorburn feigned concern, while knowing exactly what had happened to her.

"You even assisted in the search for the child after you had reported her missing to police," Justice Boddice said.

About 8pm on the evening of October 30, Thorburn told his wife Julene he had something to do and not to ask questions.

After backing his car into a garage and spending about half an hour there, he took off to dispose of Tiahleigh's body.

Three hours later he returned home covered in dirt and told his family "it's done".

Foster Father Sentenced To Life In Prison For Tiahleigh Palmer Murder

In that time, Thorburn had taken Tiahleigh's corpse to the Pimpama River, stripped her naked except for her underwear and dumped her body near its banks in a secluded area.

"You showed no respect for her, even in death," Justice Boddice said.

When Tiahleigh's body was found six days later by three fishermen, it was so decomposed no cause of death could be determined.

There were no obvious injuries apart from a bruise to the skull.

After killing Tiahleigh, Thorburn made deliberate and sustained deceptions to try to cover up his crimes.

He and his family lied to police throughout months of their investigations and in Crime and Corruption Commisison hearings.

But their story came undone when police bugged the family home for a month. In secretly recorded conversations, Thorburn demanded the family persist with their lies and coached his wife and two sons about what to say.

In his bogus version of events, Thorburn said Tiahleigh had stayed in bed on the night she was murdered, he had driven her to school the next morning and had seen her greet a friend.

Tiahleigh's biological mother, Cindy, lamented that Thorburn killed a beautiful girl with her life ahead of her.

"Rick Thorburn took that away from me, from our family and most of all Tiahleigh," she said outside court.

Thorburn will first be eligible for parole in September 2036.

With AAP.