Tiahleigh Palmer's foster brother's alleged sexual relationship with the slain Logan schoolgirl may not have been the first time he was involved in such conduct, a court has heard.
Incest-accused foster brother Trent Jordan Thorburn will spend Christmas behind bars after he was refused bail in the Supreme Court on Wednesday.
Police raised fears he would offend against other children but the judge, who noted allegations the defendant had offended against another underage girl previously, was more concerned that he may potentially interfere with other witnesses.
The 19-year-old wasn't required in court for the hearing, on the same day his father faced court accused of murdering Tiahleigh.
Richard Thorburn, 56, allegedly murdered Tia at their Chambers Flat home in an attempt to cover up his son's alleged sexual involvement with the 12-year-old.
Trent is accused of perverting the course of justice throughout the 11-month investigation into Tia's disappearance and lying to a Crime and Corruption Commission star chamber on two occasions.
In opposing bail, prosecutors argued they had a strong case against the teenager, which his defence did not disagree with.
Legal Aid barrister Catherine Morgan claimed the accused wasn't the "instigator" of plans to lie to cover up the alleged murder, saying he had an inappropriate relationship with the girl before "events outside of his control occurred".
But prosecutors argued this was not relevant, saying he was an "enthusiastic participant thereafter".
Police had also argued Mr Thorburn was an unacceptable risk of offending against other children if released.
"I do note there is material exhibited … that suggests the alleged offending between the applicant and an underage girl with Tiahleigh is not the first occasion that he might have been involved in that kind of conduct," Justice Bond said.
He said a prohibition from unsupervised contact with children would negate the risk denied bail to the Logan man, finding he was an unacceptable risk of interfering with witnesses and failing to appear.
His decision was greeted with hisses of "yes" from the public gallery, where Tia's mum, Cindy, sat with a small crowd of purple-shirted supporters.
They enjoyed a group embrace inside the court house before Ms Palmer emerged to tell waiting media it was only fair that if Tiahleigh couldn't see her family at Christmas neither could her foster brother.
"I'm really relieved actually. I think it's a great outcome," she said.
Richard Thorburn's murder charge was mentioned in the Beenleigh Magistrates Court on the same day, where defence lawyer Adam Dwyer said he was seeking a psychiatric evaluation.
The Logan schoolgirl was last seen alive at Marsden State High School, south of Brisbane, on October 30.
Mr Thorburn, 56, claimed he dropped Tiahleigh off at Marsden State High School that morning.
A missing person alert was issued six days later, hours before three fishermen found her body on the banks of the Pimpama River.
Foster mother Julene Thorburn, 54, and her son Josh, 20, last month pleaded guilty in the Beenleigh Magistrates Court to one count each of perjury and attempting to pervert the course of justice.
Outside court at the time, Gold Coast lawyer Jason Jacobson said his clients were prepared to assist the prosecutors as witnesses against Mr Thorburn.