It was "virtually impossible" to prevent a mother's actions behind the wheel before she died in a crash with her four children, a coroner has found.
However, the findings into the deaths of Charmaine McLeod and her two daughters and sons have been dismissed as a "waste of time" by a family member.
Coroner Kerrie O'Callaghan on Wednesday said Ms McLeod, 35, was at the wheel when her car collided with a truck on the Bunya Highway at Kingaroy, northwest of Brisbane, in May 2019.
She died on impact along with her children Aaleyn, 6, Matilda, 5, Wyatt, 4, and Zaidok, 2, before the car was engulfed in flames.
The coroner found Ms McLeod's actions were deliberate.
"It was a devastating tragedy that caused unimaginable grief for the father (James McLeod)," Ms O'Callaghan said, handing down her inquest findings.
The 2023 inquest had been told Ms McLeod had a complex mental health history, suffering from untreated borderline personality disorder along with suicide attempts.
She and Mr McLeod had four children before separating in 2017, sparking a custody battle.
She had made allegations against Mr McLeod of threatening behaviour and sexual abuse after their separation, the coroner was told.
Mr McLeod denied the allegations to police at the time and his barrister challenged them at the inquest.
The coroner found the police investigation into Ms McLeod's allegations of domestic violence and child abuse was "adequate and appropriate".
Ms McLeod had complained that police were not keeping her safe and the legal system was letting her down, culminating in a sense of hopelessness.
"It is apparent Ms McLeod perceived that she was in a desperate situation," Ms O'Callaghan said.
On the night of the crash, Ms McLeod received an email that she perceived indicated she was going to lose custody of her children to her former partner.
This triggered a "dramatic" response, the coroner said.
Ms O'Callaghan was unable to determine whether the crash was an act of revenge against Mr McLeod over the custody battle or whether she had "acted protectively" toward her children.
The coroner was tasked with investigating how police, support services and children protection agencies responded to Ms McLeod's allegations of domestic and sexual abuse and her mental health struggles.
She also sought to find out whether the deaths could have been prevented.
"No one could have predicted her suicide or filicide of her children," Ms O'Callaghan said.
"Ultimately I conclude even with a different approach to those issues the death of Ms McLeod and her children would not have been prevented."
The coroner made no adverse findings against police responses to the domestic violence and sexual abuse allegations.
Neither did she make adverse findings for the individuals or health and support services assisting Ms McLeod in her mental health battle.
Agencies responsible for children's protection, safety and welfare also appropriately responded to Ms McLeod.
But Ms O'Callaghan recommended better training, support and guidelines for legal practitioners who have clients experiencing domestic and family violence and complex mental health issues.
"The murder and suicide was virtually impossible to prevent by the agencies," she said.
Mr McLeod declined to comment outside the Coroners Court in Brisbane on Wednesday.
But Ms McLeod's father Paul Harris said the findings were a "waste of time".
"Waste of time, waste of money, waste of resources," he told reporters.
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