Police rushed to the scene in Clarkson in February last year.  (ABC News: West Matteeussen)

A 32-year-old man accused of killing his father at his home in Perth’s north told police “someone” had told him to commit the murder, the court heard on the first day of his trial at the WA Supreme Court.

David Nadi Lamie Moussa, who is facing a judge-alone trial, has pleaded not guilty on the grounds of insanity to one count of murder and one count of grievous bodily harm.

Prosecutor Kim Jennings told the court that on February 4, 2025, Mr Moussa stabbed his father, Nadi Moussa, 72, with a Japanese kitchen knife outside his Clarkson home after he drove from Queensland, where he was living at the time, to Western Australia.

A psychiatrist told the court that Mr Moussa could have been experiencing psychosis from a “combination of medication and stress” and that he believed that killing his father was morally right.

Mr Moussa’s stepmother, Theresa Awad Soliman, 52, was also stabbed when she tried to disarm him.

‘I killed my father’

The court heard Mr Moussa was taking dexamphetamine to treat ADHD, and medicinal marijuana, which he allegedly obtained online, to treat Crohn’s disease.

The court was shown video footage from a neighbour’s camera and heard the recording of the Triple Zero call Mr Moussa made after attacking his father.

On the call, Mr Moussa could be heard telling the operator: “I killed my father.”

When the operator asked Mr Moussa why he did that, he said: “I remembered things he did to me when I was young.”

In his evidence, psychiatrist Adam Brett said he believed Mr Moussa had been unwell for at least six months in the lead-up to his father’s murder.

Dr Brett said Mr Moussa had been experiencing consistent delusions about his father and that he believed those delusions to be true.

But after further enquiry, Mr Brett confirmed Mr Moussa “had a normal childhood” and there was “no evidence of abuse”.

The court heard that before the incident, Mr Moussa took his half-sister, who was aged six, outside the house. He told police he did that because he did not want her to witness what he was about to do.

Mr Moussa then returned to the living room, where his father and stepmother were, and told them he wanted to kill them.

When the father walked away to see where his daughter was, Mr Moussa followed him and stabbed him twice.

The court heard that the father told his daughter to run before hiding behind his car, where Mr Moussa stabbed him several times.

He then called the emergency services.

The trial continues.