Having already killed his grandmother and led police on two dangerous pursuits, Murray Deakin snarled when a retired police officer approached him on a country NSW road.
"Follow the code ... you have to follow the code," the expressionless 22-year-old told Michael 'Mick' Horne in June 2018.
He sighed when Mr Horne asked for his name and pulled a claw hammer from his backpack, striking the fleeing 54-year-old in the back of the head.
Melanie Horne witnessed her husband's final moments before Deakin ordered her out of the couple's ute and drove away.
The NSW Supreme Court on Monday heard Deakin accepts he killed Mr Horne, 54, and Gail Winner, 69, on the Far South Coast on June 1, 2018.
But he has pleaded not guilty to murder on the grounds of mental illness, the trial was told.
"We rely on psychiatric evidence that on the balance of probabilities, Mr Deakin was in fact suffering the prodromal stages of schizophrenia not only immediately before, but for some years before the 1st of June (2018)," Deakin's barrister, Julia-Ann Hickleton, said.
Deakin has also pleaded not guilty on mental illness grounds to causing grievous bodily harm with intent to murder his grandfather, Thomas Winner, then 71.
Noting it wasn't a medical opinion, Ms Hickelton said she intends to place weight on Mr Winner telling police on June 1 his grandson "lost it" and was "a schizophrenic".
Prosecutors disagree that Deakin's psychosis and subsequent homicidal actions stemmed from mental illness.
"The Crown argues it is a drug-induced psychosis," Neil Adams SC said, alleging Deakin had consumed cannabis and LSD prior to the two homicides.
"It's common ground between the Crown and the defence that he knew what he was doing.
"But the issue is whether he knew what he was doing was wrong."
Agreed facts state Deakin arriving back at the Winners' Bega home about 3.30pm on June 1 found his motorbike had been moved.
Using a pen-knife to stab his grandfather in the chest on the front doorstep, Deakin then chased down his grandmother as she ran to her car, stabbing her in her chest, neck and back.
Mr Winner was stabbed another four times as he tried to wrestle the knife from his grandson.
Deakin then drove his grandparents' car erratically and at speed through Bega towards the coast.
Police called off two pursuits for safety reasons, including when a prime mover with a trailer was forced to evade the oncoming Deakin on a two-lane highway.
The damaged car was later spotted by Mr Horne, a retired senior constable as he and Ms Horne drove home from Merimbula.
The couple followed until Deakin parked beside a road outside Tura Beach and began walking up a driveway towards a house.
As her husband walked after Deakin, Ms Horne stayed in the car, filming Deakin and talking to emergency services.
Her footage caught her husband turning and running back to the car while the recorded triple-zero call captured a screaming Deakin ordering Ms Horne from the car.
He was arrested at gunpoint about four hours later after crashing the Hornes' ute in nearby forest.
Ms Horne flagged down help minutes after the attack but her husband died of his injuries on June 3 in a Sydney hospital.
The trial, which Justice Robert Beech-Jones is hearing without a jury, adjourned early on Monday after Deakin became unwell.
It's due to resume on Tuesday.
Australian Associated Press
