The foster brother of murdered Queensland schoolgirl Tiahleigh Palmer allegedly told a cousin in a Facebook message that he had sex with the 12-year-old and feared she might be pregnant, a court has heard.

Police prosecutor Sergeant Elen French alleged Tiahleigh told a friend that she had sexual relations with her 19-year-old foster brother Trent Thorburn, and also told the friend she had “disclosed this to her foster mother (Julene Thorburn)”.

Trent’s father – and Tiahleigh’s foster father – Rick Thorburn, 56, has been charged with murdering the schoolgirl.

Authorities had been working off the theory that Tiahleigh disappeared after being dropped off at Marsden State High School by Rick Thorburn, on October 30 last year, but the Courier Mail has reported police now believe Tiahleigh Palmer was killed the night before.

Trent Thorburn, who has been arrested in connection to the murder of Queensland schoolgirl Tiahleigh Palmer.

The paper alleges Tiahleigh never made it to the school and died the night before, after Thorburn allegedly learned that Trent had been having sex with her.

The Courier Mail also reported Tiahleigh chose to stay with the Thorburns rather than return to her biological mother’s care because she had developed a “crush” on Trent Thorburn.

“She said she wanted to stay because of the boy and because she loved the horses on the property that they have there,” her grandmother Sue Palmer told the paper.

“We didn’t have any idea what was actually happening there – just that she had a crush on the boy and that he was the main reason she wanted to stay.”

Speaking in Beenleigh Magistrates Court on Wednesday, Sgt French said Trent “abused his position as big brother and took advantage of her” and “the consequences of that are her young life has been taken”.

The prosecution said Trent Thorburn was asked on five separate occasions if he had sexual relations with Tiahleigh or was involved in her death, and on each occasion he denied it.

A request by Trent Thorburn’s lawyer that he be granted bail was dismissed by magistrate Pamela Dowse.

Meanwhile, Rick Thorburn was unable to face court on Wednesday after being placed into an induced coma after collapsing at Beenleigh police watch house, south of Brisbane, on Tuesday.

He was rushed to the Princess Alexandra Hospital, where he remained in the intensive care unit.

Rick Thorburn’s lawyer, Kelly Thompson, declined to confirm media reports his condition was caused by self-harm.

“He’s currently in an induced coma and there’s no indication as to when he might be brought out of that at this stage,” Ms Thompson said.

Facing charges of incest as well as perjury and perverting the course of justice, Trent Thorburn showed little emotion from the dock as allegations of his abuse of Tiahleigh were read out to the court.

Police also allege Tiahleigh herself revealed Trent Thorburn’s criminal behaviour in a conversation with a friend shortly before her disappearance.

Sgt French said Tiahleigh had said “Trent tried to touch me” to her friend.

It was also claimed Tiahleigh had informed her foster mother Julene Thorburn, but the 54-year-old had taken no action against her son.

Among those attending the court hearing were the Marsden State High School student’s biological mother, Cindy Palmer.

She declined to comment to the media, but was flanked by a group of supporters who wore white T-shirts with the words “# Justice 4 Tiahleigh”.

Tiahleigh’s biological mother Cindy arrives at court. Photo: ABC

The supporters also included Tiahleigh’s former foster father Wayne Pemberton and his son Cameron, who cared for the “feisty” 12-year-old for two-and-a-half years before the Thorburns.

Cameron Pemberton said the murder came as “a total shock, you don’t expect that from a carer”.

Magistrate Pamela Dowse denied Trent Thorburn bail, adjourning his matter to November 9.

On Tuesday, Julene Thorburn, 54, and another son, Josh, 20, were charged with perjury and perverting the course of justice.

Both were bailed and ordered to return to court on October 10.

Questions raised over carers

The allegations against the Thorburns also raised questions about the selection of carers in Queensland.

Child Safety Minister Shannon Fentiman revealed on Wednesday the Thorburns had been approved as foster carers in August 2014.

The family had also operated a day care centre, Ms Fentiman said, before police shared intelligence about the family with authorities in April.

“Their family day care approval was immediately revoked and their foster care approval was immediately suspended,” Ms Fentiman said.

Opposition Leader Tim Nicholls said the case showed the need for an investigation into the state’s foster care system.

But Foster Care Queensland executive director Bryan Smith defended the system, telling AAP the state had “one of the most in-depth and stringent arrangements around the approval of foster carers in Australia”.

Charges laid against the four members of the Thorburn family:

Members of the Thorburn family: Richard, Josh, Julene and Trent.

* Foster father Richard Thorburn: Charged with murder and interfering with a corpse.

* Foster brother Trent Thorburn: Charged with incest, attempting to pervert the course of justice and two counts of perjury.

* Foster brother Josh Thorburn: Charged with perjury and attempting to pervert the course of justice.

* Foster mother Julene Thorburn: Charged with perjury and attempting to pervert the course of justice.

– with agencies