Two brothers have been found guilty, for the second time, of the revenge murder of a Perth businessman whose body was found wrapped in black plastic in the rear of his own vehicle.

Key points: Ambrose and Xavier Clarke faced two trials for the murder of Peter Davis

Ambrose and Xavier Clarke faced two trials for the murder of Peter Davis Mr Davis, their former business partner, was beaten before being put in his car

Mr Davis, their former business partner, was beaten before being put in his car Both brothers said they were framed for the murder by a group of Estonians

Ambrose and Xavier Clarke were first found guilty in 2013 of murdering 57-year-old Peter Davis.

After they had served about five years of their life jail terms, their convictions were quashed on appeal and a retrial ordered.

That retrial took four months and ended on Tuesday with a second Supreme Court jury finding both men guilty of the crime.

The court was told the brothers had lured Mr Davis to a business in Malaga in May 2011, where he was beaten about the head and upper body before being put in the back of his own vehicle and driven to a Rivervale motel.

Peter Davis's body was found in the back of his own utility. ( Supplied: Davis family )

Mr Davis's body was found when his son Kurt, who was searching for his father, drove randomly into the carpark of the motel and saw Ambrose Clarke in the passenger seat of another car.

That led to what was described as a "demolition derby", with Kurt Davis's car being rammed by the other vehicle before it managed to escape and sped off.

Brothers claimed Estonian worker alibi

It was argued at the brothers' 2013 trial that Mr Davis took three to six hours to die in the back of his vehicle after suffering injuries consistent with blunt force trauma and some kind of smothering.

At the retrial, prosecutors said the 57-year-old, who had undiagnosed heart disease, died as a result of cardiac arrhythmia — a fatal heart condition.

But they argued the assault had significantly contributed to it, and therefore to Mr Davis's life being ended.

The court was told the motive was revenge for a perceived debt of $300,000 that Ambrose Clarke, 54, believed was owed to him by Mr Davis after their business relationship ended badly in 2009.

While Xavier Clarke, 52, had never met Mr Davis, prosecutors alleged he was "the loyal brother" who assisted in ending the 57-year-old's life.

It was also suggested by prosecutors that a third, unknown, person could have been involved in the assault.

Xavier Clarke's lawyer said he had never met Peter Davis. ( ABC News: Hugh Sando )

Both men have always maintained their innocence, claiming at the retrial that a group of Estonian men, whom Ambrose Clarke had once employed casually, could have been responsible for the assault on Mr Davis for their own financial reasons.

Defence lawyers suggested the Estonians then "planted" incriminating evidence, found two months after the murder, in the open carport of Ambrose Clarke's home.

That evidence included one of Mr Davis's two phones and a page from his diary.

Heart condition made victim 'dead man walking'

The defence also said the "causation" of Mr Davis's death was a crucial issue in the case, claiming it could not be proven beyond a reasonable doubt the alleged assault had actually led to his death.

Barrister Shane Brennan, who represented Ambrose Clarke, described Mr Davis as "a dead man walking" because of his undiagnosed heart disease and maintained the injuries he suffered, which were not life-threatening, could have been inflicted after he was dead.

Ambrose Clarke was spotted by Mr Davis's son while he was out looking for his missing father. ( ABC News: Hugh Sando )

Barrister Jonathan Davies, who was Xavier Clarke's lawyer, argued the evidence did not prove that his client was even present when Mr Davis was assaulted.

Mr Davies also claimed the police investigation was incomplete, telling the court that the Estonian men, who had the opportunity and the motive to assault Mr Davis, were not properly investigated.

The jury deliberated for just over a day before reaching the verdict.

Both men were remanded in custody and will face a sentencing hearing in September.

Their family members packed the public gallery and cried and hugged each other after the verdicts were delivered.

'A little bit of hell on Earth'

Outside the court, Peter Davis's wife, Jenni, described the past eight years as "a little bit of hell on Earth", and said having to sit through the trial twice was horrendous.

Ms Davis also said it was difficult knowing her husband's murderers were out on bail.

"You're looking over your shoulder, not that we've had any threats or anything like that, but you're constantly in fear … if they do it once they can do it again," she said.

Jenni Davis described the verdicts as "pure and simply justice". ( ABC News: Jon Sambell )

But she said she was very pleased with the latest verdict.

"Just so happy … two juries, two times, it's just the best news and … it's just amazing we can now perhaps get on with our lives," she said.

"Twelve people two times can't be wrong and it's justice. It's pure and simply justice."

'We will appeal again and again'

One of Ambrose and Xavier Clarke's relatives, Adrian Bertino-Clarke, said he found the verdicts shocking.

"The directions given by the judge were so clear that we can't understand how the jury reached that verdict," he said.

"This destroys our confidence in the jury system … we're completely shocked by this outcome.

"We will appeal again and again until justice is achieved."

Adrian Bertino-Clarke (centre) with other family members who say they are "shocked" by the verdicts. ( ABC News: Jon Sambell )

Ambrose Clarke's daughter, Phoebe, said the case was too complex for the jury to fully understand.

"It just highlights the fact that the causation and the DNA evidence, they were too scientifically complex for laymen to deal with," she said.

"This case should never have been given to a jury … it's far too complex.

"Our family is again devastated and heartbroken."