A man who stabbed his parents to death had a long history of drug use and mental health issues, including paranoid delusions, a court has been told.
Graeme Leslie Murray admits killing his parents in their home at Oberon, in the NSW Central Tablelands region, in the early hours of August 13, 2021.
The 49-year-old is asking a judge-alone murder trial, which started in the NSW Supreme Court on Monday, to find him not criminally responsible for their murders by reason of mental impairment.
Police found the bodies of Glenn Murray, 68, and Susan Murray, 66, shortly after they were stabbed multiple times and left face down in pools of their own blood, crown prosecutor Paul Kerr told the court.
Mrs Murray was dressed in her pyjamas in the family's laundry, having been stabbed eight times to the face chest, abdomen and upper arm.
Her husband had been stabbed 14 times to the chest, neck, back and arm, and did not display any defensive injuries, the court was told.
Murray's lawyer Tom Quilter said there was no dispute his client had committed the killing, but he was suffering a psychotic break at the time.
"The principal defence in this case is one of the defence of mental health impairment," he said.
Murray had a long history of mental health issues including paranoid delusions, which those close to him said became worse when he used ice.
Through multiple run-ins with police, Murray had been in and out of mental health facilities and was on one of those occasions diagnosed with drug-induced psychosis.
Delusions included the belief his house was full of cameras and listening devices, or that people were trying to hurt him or his family.
Around 2019, Murray had ceased using ice and was holding down a steady job as a labourer, the court was told.
In the week before he killed his parents, however, pandemic restrictions meant Murray was unable to work, which contributed to him relapsing.
Murray initially denied stabbing the couple when interviewed by police, but he later told psychiatrists he had killed them while suffering delusions that they were not really his parents.
Murray told psychiatrists he believed when he stabbed his mother it was "like something evil was inside her".
He admitted injecting ice prior to stabbing his parents and was seen by multiple witnesses acting erratically, telling one friend he felt "scattered" and regretted using the drug.
Toxicology revealed that at the time he killed his parents, Murray would most likely not have been feeling the acute effects ice, but the court heard drug-induced delusions can persist even after the primary narcotic effects have worn off.
Psychiatrists who examined Murray on behalf of both the Crown and defence concluded he was experiencing a psychotic episode at the time and had a psychotic disorder, which was either substance-induced or schizophrenia.
Mr Quilter told the court there was no motive other than a severe mental impairment for Murray to have killed his parents.
"My mother and father were the two nicest people I've ever met in my f***ing life," the 49-year-old told police.
"They were my best friends, my parents. I don't know why I f***ing done it, I don't."
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