Schoolgirl Tiahleigh Palmer may have been pregnant to her foster brother when she died, a court has heard.
In a bombshell revelation, the Beenleigh Magistrates Court heard yesterday morning Trent Thorburn, 19, confessed to his cousin in a Facebook message he had sex with a New Zealand family's 12-year-old daughter, his foster sister, and feared she was pregnant.
He was denied bail on four charges, including incest.
His father, Rick Thorburn, 56, is alleged to have murdered Tiahleigh, his foster daughter, in October, 2015, in a bid to cover up his son's alleged crime.
Tiahleigh's Kiwi biological mother Cyndi Palmer was present for the hearing.
Police prosecutor Sergeant Ellen French said Trent Thorburn had obstructed police during the investigation and that he and his family - all of whom have been charged over her death - betrayed Tiahleigh's trust.
"The victim was put in care and protection of the defendant and his family," Sergeant French told the court.
"This defendant betrayed her trust. He abused his position as big brother and took advantage of her.
"A consequence of that is her young life has been taken."
The court heard Tiahleigh told a friend that she and her foster brother had sex.
She also told the friend she had divulged it to his mother, Julene Thorburn.
"The victim claimed (to the friend) to have disclosed this to her foster mother," the prosecutor said.
The court hearing came as Queensland's Child Safety Minister Shannon Fentiman announced a six-month review of the state's foster care system in the wake of charges relating to the Tiahleigh's murder being laid against all members of her foster family.
The 12-year-old had been living with the Thornburns for 10 months when she was allegedly murdered by her foster father.
Murder accused Rick Thorburn did not appear in court for a scheduled hearing this morning.
He is in an induced coma in hospital, his lawyer said, after collapsing while in police custody, in an apparent self-harm attempt.
He has been charged with the murder of Tiahleigh, as well as interfering with her corpse.
Trent Thorburn applied for bail in the same court.
He remains in custody on four charges, including incest, attempting to pervert the course of justice and two counts of perjury.
Earlier, the court heard his father was rushed to hospital after collapsing at Beenleigh watch-house on Tuesday night, just hours after he was charged.
The Queensland Police Service's Ethical Standards Command has launched an internal investigation into the circumstances surrounding the incident.
Rick Thorburn's lawyer told the court her client was in an induced coma in Brisbane's Princess Alexandra Hospital, where he is under police guard.
He was remanded in custody, in his absence, to reappear on December 21.
The accused killer's wife and other son have also been charged in relation to the schoolgirl's death.
Thorburn's wife, Julene, 54, and 20-year-old son Josh have each been charged with perjury and attempting to pervert the course of justice.
It is alleged the family all lied to authorities to conceal their involvement in Tiahleigh's death.
Police will allege Thorburn killed his foster daughter in a bid to cover up the sexually abusive relationship his then-18-year-old son Trent was having with the 12-year-old.
Thorburn told police he dropped Tiahleigh at Marsden State High School on the morning of October 30, 2015, but investigators are believed to have been unable to corroborate his version of events.
The 12-year-old is believed to have been killed some time the previous day.
The family's blue Ford Falcon, which was seized by police last week after being sold in the wake of Tiahleigh's death, is alleged to have been used to transport her body about 30km to the Pimpama River, where it was discovered, semi-naked, by fishermen a week after she disappeared.
The family of four was all arrested at various places in the Logan area on Tuesday before being charged.
Julene Thorburn and her eldest son Josh have been released on bail to appear in Beenleigh Magistrates Court on October 10.
Tiahleigh's Kiwi biological mother Cyndi Palmer arrived for the hearing flanked by supporters but declined to speak to reporters.
On Wednesday, Ms Fentiman revealed the Thorburns had operated a day care centre at their home until their approvals were revoked in April, when police alerted the government to alleged criminal activity.
Ms Fentiman made the revelation while announcing a six-month review of the state's blue card system, which was sparked by the criminal charges laid against the Thorburn family.
Ms Fentiman said the couple was approved as foster carers in August 2014.
"All relevant checks, including blue cards, criminal history checks, interviews and reference checks were undertaken including mandatory training," she said in Brisbane.
No other children were placed with the family after Tiahleigh disappeared in late October last year; however, police shared intelligence on the Thorburns in April.
"This was the first time concerns had been raised about the Thorburns," Ms Fentiman said.
"Their family day care approval was immediately revoked and their foster care approval was immediately suspended."
On Tuesday, Detective Inspector Damien Hansen said it was expected Thorburn's wife and sons would likely be called as witnesses in any murder trial their husband and father faced.
"(Julene Thorburn) will be a key witness, all three I expect to be witnesses," he said.
According to The Courier-Mail, the Thorburn family had been persons of interest in the murder probe, and a call to Crime Stoppers in April led to cracking the case, senior police told the paper.
Earlier this year, investigators announced a $250,000 reward and indemnity from prosecution for any person who provided evidence leading to Tiahleigh's killer.
On Tuesday, Insp Hansen hinted at a potential deal being reached with Julene Thorburn, who has engaged a lawyer.
He said discussions were ongoing in relation to, "working that out".
The family was taken into custody for questioning shortly after Insp Hanson revealed the investigation was at a "crucial stage".
At the weekend, Tiahleigh's mother took to social media to point the finger at the schoolgirl's foster father, in a post that police ordered her to remove.
Insp Hansen said the flurry of publicity that followed was "not helpful" to the murder investigation.
When approached by a Channel Nine reporter at the entrance to his Logan property prior to his arrest on Tuesday, Thorburn declined to answer questions.
Insp Hansen said the multi-agency investigation had been one of the most complicated of his career, with more than 3500 lines of inquiry to be followed.
"One person doesn't solve a homicide and particularly something like this, this is one of the most difficult I've ever worked on," he said.
"We've had dedicated police on this for a long period of time, 11 months ... it's just been a great team effort."
However, the investigation was far from over, he said.
"By no means is it over. There's a lot of work to go on with yet."
In a Facebook post at the weekend, Tia's mother, Ms Palmer, revealed publicly for the first time the car seized last week had once belonged to her daughter's foster parents.
"The car that was seized is identical to the one that ... and ... had, the one they had sold within days of Tiahleigh's body being found," she wrote.
"And as the news and police depicted this car was in the possession of a new owner who was NOT a suspect in their investigation ...
"... and ... were the carers of Tiahleigh, the people who were intrusted (sic) where her care and wellbeing, the same carers who are publicly selling up everything they own."
Insp Hansen said she was still coming to terms with the arrests of members of the family who had been entrusted with the care of her daughter.
"This has been very traumatic for her, she's asked if she can be left alone, it has affected her greatly and affected the family," he said.
Appealing for public help in the investigation in March, Ms Palmer hinted police had told her they thought more than one person was involved in her daughter's death.
"Somebody knows something about what happened to Tiahleigh," she said.
"Somebody knows something about the person or people responsible.
"I'm guessing the person or people who know about this are too loyal to whoever they're helping."
- Additional reporting AAP