A Perth father murdered his son before two of his other children buried the body and cleaned up the scene because he did not want to miss the AFL grand final, WA's Supreme Court has been told.

Ernest Fisher, 67, is on trial accused of fatally stabbing 23-year-old Matthew Fisher-Turner, whose body was found buried in the backyard of the family's Parmelia home in Perth's southern suburbs in October 2016.

He was allegedly murdered four weeks earlier, and his body was discovered 10 days after his friends reported him missing.

Mr Fisher's two children, Joshua Douglas Fisher-Turner, 28, and Hannah Jayde Fisher-Turner, 21, are also on trial accused of being accessories to the alleged murder.

State prosecutor Laura Christian said Mr Fisher told police he killed his son because the 23-year-old had wanted to use his car, but he had wanted it to go to a friend's house to watch the grand final.

"He said 'I'm not having it' and he decided that was the time to kill Matthew," Ms Christian said.

"He told police footy was a priority and he didn't want to miss the grand final."

The Western Bulldogs defeated the Sydney Swans in the 2016 AFL grand final. ( AAP: Julian Smith )

Ms Christian said Mr Fisher used two knives he got from a shed in the backyard and stabbed Matthew as he stood in Joshua's bedroom.

He is then alleged to have told Joshua: "We need to bury him. Dig it deep."

Ms Christian said Joshua and his sister Hannah used a ladder to take Matthew's body to the backyard before burying it and then cleaning the house, including removing bloodstained carpet and washing the walls with bleach.

Murder 'the only solution': prosecutor

The court was told when friends began to raise concerns about Matthew, Mr Fisher told them he had "packed his bags and left for over east with a chicky babe who had lots of money".

The friends reported Matthew missing to police, and Ms Christian said his father also subsequently told officers his son had gone over east.

Mr Fisher-Turner was "aggressive and angry" towards his family, his father's lawyer told court. ( Facebook: Matthew Fisher-Turner )

Police formally interviewed Mr Fisher on October 22, 2016, and the court was told he initially denied knowing what had happened to his son, before eventually admitting he had killed him.

"He said Matthew had pushed or punched him on occasions," Ms Christian said.

"He described Matthew as horrible, he believed he was on drugs, he described him as angry and said he owed him money.

"He said he had enough.

"The only solution he saw to the problems in his family was to kill his son."

All three accused deny the charges against them.

Court told of 'fractured family'

Mr Fisher's laywer Sam Vandongen said the issue for the jury to decide was likely to be why his client killed his son.

He said it would become "very apparent" during the trial that the family was fractured, something that started when Mr Fisher's wife died in March 2014.

A composite image of Ernest Fisher (centre) with his children Joshua and Hannah Fisher-Turner. ( ABC News: Anne Barnetson )

Mr Vandongen described her as a "lovely person who was devoted to her children" and said her death "badly affected" the family, to the extent that at the time of Matthew's death the house was "a mess", and a "pigsty."

"There was stuff everywhere in piles; piles of books, piles of clothing, dirty dishes, spider webs on the walls and the bedrooms were filthy," Mr Vandongen said.

"You might think it reflected the mood of those who lived there."

Mr Vandongen described his client as a hermit, and said Joshua spent most of his time in his bedroom, while Hanna also "appeared to be a bit reclusive".

However he said Matthew was "very different", and went to the gym and had no trouble forming relationships outside the house.

However Mr Vandongen told the court the relationship between Matthew and his family began to break down.

"Matthew was aggressive and angry," he said.

"He was violent towards Ernest. He would physically assault him. The evidence might show he directed his anger and vitriol towards his father."

Mr Vandongen said the jury would also see a video recorded on Matthew's telephone in which he was "goading" Joshua, and Mr Fisher said to him "you're breaking this family apart".

Mr Vandongen submitted his client would argue "he did what he did in order to defend himself and defend his children from Matthew … he was effectively getting in first".

The trial is set down for three weeks.