Tiahleigh Palmer's accused killer, her foster father Rick Thorburn, has woken from a medically induced coma, 48 hours after he allegedly attempted to self-harm while in custody.

Thorburn, 56, is believed to have overdosed on pills at Beenleigh watch house soon after being charged with the murder of his 12-year-old foster daughter on Tuesday.

The Queensland Police Ethical Standards Command has launched an investigation into the incident.

Queensland Police confirmed Thornburn woke from the coma today and is now in a stable condition. He has been transferred from intensive care, to Princess Alexandra Hospital's secure unit in Brisbane.

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Thorburn's wife and eldest son have returned to their rural Chambers Flat home, the scene of Tiahleigh's alleged murder, after being released on bail.

In somewhat bizarre scenes at the property on Wednesday, Julene Thorburn was seen in her yard feeding her horses, as specialist forensic police continued searching the area.

The Thorburn family, left to right, Rick, Josh, Julene and Trent, pictured in 2014. Photo / Facebook
The Thorburn family, left to right, Rick, Josh, Julene and Trent, pictured in 2014. Photo / Facebook

Police are continuing to scour the acreage, as investigations in the case continue following the laying of charges against the couple and their two adult sons on Tuesday.

Rick Thorburn was remanded in custody in his absence in Beenleigh Magistrates Court on Wednesday, where he had been scheduled to appear.

Tiahleigh's Kiwi biological mother Cyndi Palmer was present for the hearing.

Thorburn has been charged with Tiahleigh's murder and interfering with her corpse.

He is due to reappear in the same court on December 21.

Tiahleigh's backpack and school uniform have never been found. Photo / News Corp Australia
Tiahleigh's backpack and school uniform have never been found. Photo / News Corp Australia

The 12-year-old's body was dumped about 30km from the home she lived in with Mr Thorburn, his wife Julene and their sons Josh, 20, and Trent, 19.

It is alleged Thorburn killed Tiahleigh in a bid to cover up the sexual relationship his youngest son was having with her.

Trent Thorburn was denied bail in Beenleigh Magistrates Court on Wednesday, after being charged with incest.

In a bombshell revelation, the court heard that the youngest Thorburn son feared his 12-year-old foster sister had become pregnant to him.

He is believed to be considering a fresh bail application in the Supreme Court.

Julene and Josh Thorburn have both been released on bail after being charged with attempting to pervert the course of justice and perjury.

Juliene and Josh are alleged to have lied to authorities to protect their husband and father.

She and her elder son are due to appear in Beenleigh Magistrates Court on October 10.

Rick Thorburn will be transferred to the Brisbane Remand Centre when he is released from hospital.

Detective Inspector Damien Hansen described the murder investigation as the most difficult of his career. Photo / Jack Tran, News Corp Australia
Detective Inspector Damien Hansen described the murder investigation as the most difficult of his career. Photo / Jack Tran, News Corp Australia

Rick Thorburn told police investigating Tiahleigh's disappearance that he dropped her at Marsden State High School on the morning of October 30, 2015.

Detectives have been unable to corroborate that story, however, and now believe Tiahleigh was killed the previous day.

The family's blue Ford Falcon was allegedly used to transport her body 30km to the Gold Coast, where it was dumped in the Pimpama River.

Fishermen found her decomposing corpse on the banks of the river nearly a week later.

In the first major breakthrough in the investigation last week, police seized the Ford Falcon, which Thorburn sold online after he allegedly killed Tiahleigh.

It came after a tip-off to investigators.

Tiahleigh had been living with the Thorburns for 10 months when she died.

In addition to fostering, the family ran a daycare centre until six months after the schoolgirl's death.

Her grandmother Sue Palmer told the Courier-Mail Tiahleigh had the opportunity to leave the Thorburn family's property but wanted to remain.

Tiahleigh's mother, Cindy Palmer, was attempting to regain custody of her daughter when she died.

"She said she wanted to stay because of the boy and because she loved the horses on the property that they have there," Ms Palmer told The Courier-Mail.

"We didn't have any idea as to what was actually happening there - just that she had a crush on the boy and that was the main reason she wanted to stay."

Cindy Palmer, who, in a Facebook post, alerted media to the fact the car seized last week once belonged to the Thorburns, is yet to comment publicly on the charges laid over her daughter's death.

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