A court viewed footage on Tuesday of a half-naked and incoherent Bilal Fadel being processed by police following his 2020 arrest.
In the footage, Fadel's hands appear to be red with the blood of two men he allegedly stabbed, one fatally, just hours before.
Wearing a ripped pair of forensic overalls, Fadel is told by one of two officers dressed in riot gear, "if you misbehave you're going to hit the deck really hard".
The 30-year-old pleaded not guilty to murdering 40-year-old Nicholas Grayndler in the early hours of August 24, 2020, on the grounds he suffers from mental illness.
He also pleaded not guilty on mental health grounds to wounding Grant Kelly, 49, with intent to murder shortly before the stabbing of Mr Grayndler.
Mr Kelly survived the attack and told police it was Fadel who stabbed him, but that they were "best friends" and he did not know why.
The three men lived near each other at Merrylands, in western Sydney, and would regularly consume cannabis and other illegal drugs together, a judge-alone trial in the NSW Supreme Court was told on Tuesday.
On the night of the attacks, Fadel allegedly approached Mr Kelly, a single-leg amputee who was seated in a mobility scooter in the driveway of his home, saying to him, "Grant, it's either me or it's you".
Fadel allegedly produced a 30cm knife with a rusty blade from his pants and moved it towards the neck of Mr Kelly, who grabbed the blade and cut his hands in the process.
The attacker then moved behind Mr Kelly, stabbing him around the neck, back and head, crown prosecutor Sylvie Sloane told the court.
During the attack Mr Kelly allegedly screamed, "What are you f***ing doing, trying to kill me? You f***ing stabbed me, what the f***."
Fadel then left the scene without saying anything, according to Mr Kelly's account.
A short time later, a neighbour called triple zero after spotting Mr Grayndler inside his unit with a severed jugular from a stab wound to the neck.
"Mr Grayndler was unable to breath and began choking on his own blood," Ms Sloane said.
Shortly after paramedics arrived, Mr Grayndler went into cardiac arrest and was unable to be saved.
Fadel was arrested and taken into custody, where he acted erratically including talking to himself and refusing to comply with police.
Forensic psychologists Stephen Allnutt and Kerri Eagle diagnosed Fadel as suffering from a psychotic disorder most consistent with a schizophrenic spectrum disorder.
They also found Fadel's use of illicit substances most likely exacerbated his mental health difficulties and may have precipitated a psychotic illness.
Dr Eagle noted it was unlikely, although not impossible, Fadel had malingered his mental illness for several years after the stabbing.
The experts agreed Fadel most likely understood the physical quality of what he was doing and that the knife would cause damage to his victims, but he likely could not reason as to whether his behaviour was wrong.
The trial continues.
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