Rick Thorburn pleads guilty to the murder of schoolgirl Tiahleigh Palmer

Tiahleigh Palmer was killed and left on the banks of the Pimpama River. Photo / Supplied

More than two years after Tiahleigh Palmer was killed and left on the banks of the Pimpama River, her foster father Rick Thorburn has been sentenced.

Thorburn will spend the rest of his life in prison for murdering the 12-year-old. He will need to serve 20 years in prison before being eligible for parole on September 12, 2036.

In sentencing Thorburn, Justice David Boddice told the court the foster dad's actions were "cold, calculating and callous" and his conduct had been "truly appalling".

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

Justice Boddice told the court Thorburn's difficult upbringing and depression didn't excuse her brutal murder.

According to the Courier Mail, Justice Boddice said the way Thorburn left Tiahleigh's body on the riverbank showed he had no respect for her, not even in death.

At the beginning of his sentencing hearing, Thorburn wiped away tears as the judge asked him what plea he would be entering.

The pale, visibly thinner 57-year-old said he entered a formal guilty plea to murdering Tiahleigh, interfering with a corpse, attempting to pervert the course of justice and perjury.

Queen's Council Carl Heaton told the court Thorburn played the role of "concerned parent" after the 12-year-old failed to come out of school in October 2015 but he had already killed her.

Rick Thorburn with his son Josh, wife Julene and other son Trent. Photo / Facebook

Mr Heaton told the court Thorburn's son Trent, 18, had a conversation with a cousin on Facebook and said he had sex with Tia and was worried she was pregnant.

That same day, Tiahleigh complained to Rick's wife Julene of stomach pains.

Julene gave her a Nurofen and put her to bed — she was murdered hours later — and the Nurofen played a key role in determining the date of her death, October 29, 2015.

Going through the facts of the case, Mr Heaton told the court one of Rick's sons was told by their father "Tia is no longer with us, I hope you understand what that means".

Thorburn, who was 55 when he murdered Tiahleigh, has spent 619 days in custody.

Justice Boddice told the court Thorburn's criminal history was "largely relevant" to the murder case.

Tiahleigh's New Zealand mother Cindy Palmer also submitted a victim impact statement to be read on the day of his sentencing.

Thorburn was the last of his family to be in court over the murder, which gripped Australia for years.

Tiahleigh, 12, had been living with the Thorburns for 10 months when they reported her missing on October 30, 2015.

Foster father Rick Thorburn was arrested and charged in September 2016. Photo / News Corp

Rick claimed he had dropped the 12-year-old off near Marsden State High School in the Queensland city of Logan on the morning of October 30.

But when he returned to pick her up that afternoon, she never showed.

A week later, a fisherman found Tiahleigh's semi-naked, partially decomposed body on the edge of Pimpama River. It is still not known how she died.

It took police 11 months to gather strong enough evidence to charge the entire Thorburn family in relation to the 12-year-old's murder.

Rick, his sons Josh and Trent and his wife Julene were all arrested in September 2016.

Tiahleigh's New Zealand mother Cindy Palmer also submitted a victim impact statement to be read on the day of his sentencing. Photo / Supplied

Police alleged Thorburn killed Tiahleigh in order to cover up his son Trent's sexually abusive relationship with the 12-year-old.

Almost immediately after he was charged, Thorburn attempted to end his own life by overdosing on pills while in jail.

He was placed in an induced coma in Brisbane's Alexandra Hospital for a number of days but was eventually sent back to prison.

In March, Thorburn indicated he would plead guilty to murdering Tiahleigh and a judge scheduled his sentencing for May 25.

He was facing a life sentence for the murder.

Thorburn also pleaded guilty to a charge of perjury relating to alleged lies he told about her disappearance and interfering with a corpse.

In 2015, few suspected the Thorburn family could be behind Tiahleigh's death.

At his foster daughter's funeral, Rick was one of the six pallbearers wearing a bright purple shirt bearing the words "Tiahleigh RIP".

In March, hours after Thorburn indicated he would plead guilty to all charges, Tiahleigh's mother Cindy Palmer said she hoped the father's sentence would finally be the end of the painful case.

"My beautiful daughter Tiahleigh deserves justice. I hope it comes on May 25th. Thank you, everyone ... I have lots to say, but right now, I will let the police and court do their job. Tia, I love you," she told the ABC.

Tiahleigh, 12, had been living with the Thorburns for 10 months when they reported her missing on October 30, 2015. Photo / Supplied

Thorburn's two sons and wife were also jailed in connection to her murder.

Trent, who admitted to having sex with his foster sister, was jailed in September 2017 for a maximum four years after pleading guilty at the Beenleigh District Court to four charges, including incest.

With time served, after spending 16 months in prison, he was released on parole on January 19, 2018.

His mother Julene spent six months behind bars after pleading guilty to perjury and attempting to pervert the course of justice in November 2017. She was released earlier this month.

The Thorburn's eldest son Joshua, was sentenced to three months in jail in July 2017 after pleading guilty to the same charges as his mother.

On the day of Joshua's release, Tiahleigh's biological mother Cindy slammed his freedom on her Facebook page #Justice4Tiahleigh.

"It has been brought to my attention that … Josh Thorburn will be saying goodbye to his old life in prison and will (today) be let out to move on with and live a fulfilling life," Ms Palmer wrote.

"He will be able to put this whole thing behind him and go on with his life. Just another kick in the face to show you how much more rights/protection and leniency criminals have these days," she added.

KEY DEVELOPMENTS IN TIAHLEIGH'S CASE

Oct. 30, 2015: Tiahleigh's foster father Rick Thorburn says he dropped the 12-year-old at Marsden State High School. It was the last time she was seen alive.

Nov. 5, 2015: Three fishermen find a girl's body on the banks of the Pimpama River on the Gold Coast. It's later confirmed to be Tiahleigh.

Nov. 14, 2015: Tiahleigh is remembered as a "beautifully imperfect" girl at her Gold Coast funeral, where Thorburn was a pallbearer.

Feb. 15, 2016: Police offer a $250,000 reward for information to solve the schoolgirl's murder.

March 14, 2016: Biological mother Cindy Palmer makes a public appeal to help find her daughter's killer.

Sept 20, 2016: Rick Thorburn is charged with Tiahleigh's murder. Foster mother Julene and their sons Trent and Joshua are also arrested. Trent is charged with incest, perjury and attempting to pervert the course of justice. Julene and Joshua are charged with perjury and attempting to pervert the course of justice.

Sept 21, 2016: Rick Thorburn fails to face court after a reported overdose.

Sept 23, 2016: Detectives say the foster family's home is a primary crime scene.

June 28, 2017: Rick Thorburn is committed to stand trial for murder.

July 27, 2017: Josh Thorburn is sentenced to 15 months' jail after admitting to perjury and attempting to pervert the course of justice.

Sept 14, 2017: Trent Thorburn is sentenced to four years' jail after admitting he had sex with Tiahleigh.

Nov. 3, 2017: Julene Thorburn is sentenced to 18 months' jail for perjury and attempting to pervert the course of justice, with the sentence suspended after six months.

Jan 19, 2018: Trent Thorburn is released on parole after 16 months behind bars.

Feb. 16, 2018: Rick Thorburn seeks a judge-only trial due to publicity surrounding the case.