A Perth man who was experiencing hallucinations and delusions when he fatally stabbed his mother, eight-year-old brother and 15-year-old sister has been acquitted of their murder on the basis that he was of unsound mind.
Teancum Vernon Petersen-Crofts, 21, killed his mother Michelle Petersen, 48, brother Rua and sister Bella at their Ellenbrook home on July 15, 2018.
He faced a judge-alone trial in the WA Supreme Court after pleading not guilty to their murders on insanity grounds.
Chief Justice Peter Quinlan on Monday said he was satisfied beyond reasonable doubt that Petersen-Crofts had killed his family members but that he was not criminally responsible for doing so because of his mental illness.
Petersen-Crofts, who has been diagnosed with schizophrenia and is being supported by family members, will continue to be detained in a secure psychiatric facility.
Justice Quinlan said he was satisfied that Petersen-Crofts had been deprived of the capacity to control his actions at the time of the killings.
He accepted that Petersen-Crofts had experienced hallucinations and delusions including "commands and instructions" from various deities.
"The voices were telling you that you must kill your family to save yourself and to save the world," Justice Quinlan said.
"Those commands were delusions but I find they were real to you at the time, as real as I am speaking to you now."
The trial heard Ms Petersen had been attempting to get help for her son and had told friends she feared for herself and her younger children because of his increasingly bizarre behaviour in the weeks leading up to the killings.
Psychiatrists told the court he had displayed symptoms of a psychotic disorder since the age of 14 when first admitted to hospital in his native New Zealand.
But Justice Quinlan said Petersen-Crofts had never received adequate or sustained anti-psychotic treatment.
"A criminal trial is not the time or the place to consider how the community can better help people like you who suffer daily from serious mental illnesses," the judge said.
"But it is still true to say, Mr Petersen-Crofts, that we, the whole community, have failed you. And we failed your mum and your sister and your brother, and we failed your grandmother and the rest of your family whose loss is indescribable."
The trial heard Petersen-Crofts turned up at his local police station on July 13, shirtless and sweating profusely and claiming his neighbour was a serial killer.
He was detained and transferred to the emergency department at St John of God Hospital in Midland, where doctors said he was likely floridly psychotic.
But the following morning he appeared calm and doctors agreed to discharge him, despite his mother's concerns.
Forensic psychiatrist Daniel de Klerk told the court Petersen-Crofts had been admitted as an inpatient with psychotic symptoms on 12 occasions and presented at emergency departments many more times.
He said he was surprised Petersen-Crofts had not "been taken more seriously" by doctors at St John of God Hospital.
"The outcome could have been very different had he been admitted," Dr de Klerk said.
In a recorded police interview the day after the slayings, Petersen-Crofts claimed his neighbour was a serial killer and blamed him for killing his family members.
Later in the interview, he said a deity named "Big Papa" had committed the crimes.
He also claimed he had "saved four billion people last night" and repeatedly stated "put me on death row" before refusing to answer further questions.
The trial heard harrowing evidence about the killings, including that each of the victims received between 44 and 54 stab wounds from a large kitchen knife.
Bella was still alive in the backyard, softly pleading for help, when police arrived. She died on the way to hospital.
Petersen-Crofts was arrested outside a nearby service station after showing up in an agitated state with blood on his hands, telling a worker he had just killed his mother and siblings.