Rick Thorburn thought he had gotten away with murder. He thought his family would stay loyal and maintain the fictional charade of innocence.

It was an exhaustive cover-up and for more than six months they kept the charade going until self-preservation kicked in.

Confronted with strong evidence — an anonymous tip-off and surveillance recordings — his wife Julene and son Josh Thorburn eventually rolled over and told police Rick Thorburn was responsible for Tiahleigh Palmer's death.

On Friday, Thorburn received a life sentence for the schoolgirl's murder.

Tiahleigh's body was found on the banks of the Pimpama River on the northern Gold Coast. ( AAP/Qld Police )

Superintendent Kerry Johnson said Thorburn tried to throw police off the scent for months after Tiahleigh's body was found on the banks of the Pimpama River in November 2015.

"He's done a number of things, and it's not just reporting her missing … being the face of a lot of public requests for assistance, all the way through to carrying her coffin," Superintendent Johnson said.

His colleague Detective Inspector Damien Hansen said of Thorburn: "He was quite plausible. He was a good liar."

On April 13, 2016, the day Tiahleigh would have turned 13, Thorburn threw her a birthday party and invited her school friends.

Louie Naumovski, who runs the Logan House Fire Support Network charity, attended the party and said he clearly remembered the sombre day on which everyone sang Happy Birthday to the dead girl.

Thorburn was right there as the face of the event.

"He's there telling me about how she was loved, how she would have been 13," Mr Naumovski said.

"He started crying. It was horrendous how we fell for it."

Rick Thorburn [L] helps carry Tiahleigh's coffin at her funeral. ( AAP: Dan Peled )

Thorburn, a one-time truck driver who branched out into operating food vans, continued to run a childcare centre with his wife Julene from their home in Chambers Flat, south of Brisbane.

Behind the scenes, Thorburn was piling pressure on the members of his immediate family to ensure they kept the truth hidden from the outside world.

The terrible truth was that on October 29, 2015, after Trent Thorburn told his parents he was frightened his incestuous abuse of Tiahleigh had gotten her pregnant, Thorburn made the decision to end her life.

Later that night, when Rick was alone in the house with Tiahleigh, he killed her.

Rick was relying on his family's loyalty to keep the dark secret. He expected no less, and his sons feared him, believing a story he once told them that he had killed before and gotten away with it.

But after police offered a $250,000 reward for information leading to the killer's conviction, an anonymous tipster came forward to tell investigators about Trent's incestuous secret — a strong motive for murder.

The family lied when they were hauled before the Crime and Corruption Commission, maintaining the story that Tiahleigh had been dropped off at school.

They were caught out when police bugged their home and captured incriminating evidence.

Police excavate an area behind the Thorburns' Chambers Flat home searching for evidence. ( AAP: Dan Peled )

In one conversation, he was recorded telling Julene: "No, but don't you tell anyone ever, no matter what — that's when things will f*** up."

When other family members were arrested and finally admitted the truth, it was all over for Thorburn.

"He was very agitated. He didn't see it coming," Detective Inspector Damien Hansen said.

"We had a very strong circumstantial case and they were the extra that we needed."

The killer himself refused to cooperate with police and maintained his right to silence.

In 2017, he was committed to stand trial for murder, perjury, interference of a corpse and attempting to pervert the course of justice.

He has never told police, nor his family, how he killed Tiahleigh.

Police still are not sure how she died because her body was so badly decomposed when it was found on the riverbank.

All they found was a bruise to her head and traces of a painkiller in her system, which helped them pinpoint the time of death being on the night of October 29.

Police search the Pimpama River on the Gold Coast where Tiahleigh Palmer's body was eventually found on the banks in November, 2015. ( ABC News: Gordon Fuad )

Despite eventually pleading guilty, Thorburn still has not helped investigators.

"I'd love to hear from his own mouth what he did and why he did it," Inspector Hansen said.

"If Rick was doing something he'd look after himself before he looks after his family."

Thorburn will not be eligible for parole until September 2036, by which time he will be 76 years old.

It will be up to the discretion of the parole board if he is ever granted freedom.

As he stood in the dock of the Brisbane Supreme Court, tears welled in his eyes and his face turned red as he uttered the word "guilty" to the court when the charges were read out to him.

Surrounded by Tiahleigh's family, police and guards, Thorburn was exposed.

He no longer thought he was untouchable.