A Perth man stabbed his aggressive 23-year-old son to death then left two of his other children to bury the body while he watched the AFL grand final, his trial has been told.
The body of Matthew Kyle Fisher-Turner was discovered in late October 2016 buried in the backyard of the family's Parmelia home and it's believed he was killed almost four weeks earlier.
Ernest Albert Fisher is charged with murder while two of his other children, Joshua Douglas Fisher-Turner, then 26, and Hannah Jayde Fisher-Turner, then 19, are on trial accused of being accessories to murder.
Prosecutor Laura Christian told the Supreme Court of Western Australia on Monday that Fisher, then 65, stabbed his son two or three times with two sharp knives, puncturing his aorta and a lung.
Ms Christian said an argument erupted after Mr Fisher-Turner wanted to borrow his car, because Fisher was keen to drive to friends to watch the AFL grand final.
He told detectives he'd said "I'm not having it" and football was his priority that day.
After the killing, Fisher started digging a grave in the backyard then left the house to watch the match, leaving it up to Joshua to bury his brother and clean up blood, while Hannah helped carry the body outside on a ladder, Ms Christian said.
"Dig it deep," Fisher told them, according to Ms Christian.
Days later, Fisher told the deceased's concerned friends his son had "gone over east with a chicky babe", initially telling police he presumed he'd travelled to Brisbane to see a girl he met on Facebook.
But when detectives said they believed Mr Fisher-Turner had never left the house and had died there, Fisher confessed, describing the victim as "horrible", claiming he was using drugs and behaved very aggressively.
Fisher's counsel Sam Vandongen said his client admitted killing his son when he realised lying was pointless and also conceded he'd instructed at least one of his other children to dispose of the body.
Mr Vandongen argued Fisher acted in self-defence, although the threat was not imminent.
"He did what he did ... in order to defend himself and defend his children," the lawyer said.
He said the pair had been badly affected by the family matriarch's death from cancer in March 2014.
"Cracks began to appear within the family," Mr Vandongen said.
The accused trio became reclusive, and while Mr Fisher-Turner kept fit at the gym and socialised outside the house, he directed his anger and vitriol towards his family, physically assaulting his father several times, Mr Vandongen said.
The trial continues.