Cassius Turvey killing: Mitchell Forth loses appeal against nine-year manslaughter sentence

One of the men convicted of killing Perth teenager Cassius Turvey, who died following a savage after-school beating, has failed in his appeal against his nine-year jail sentence, which he claimed was "manifestly excessive".

Cassius Turvey, 15, was chased down and beaten with a metal trolley pole while walking with friends in Perth's east, in October 2022. He died in hospital 10 days later.

Two men, Jack Brearley and Brodie Palmer, were convicted of murdering him.

A third man, Mitchell Forth, who was 24 at the time of the killing, was convicted of manslaughter and sentenced to nine years in prison.

Forth was not present in the moments when Cassius Turvey was bashed but was seen encouraging the chase and later celebrated with Palmer and Brearley over what had happened.

Forth argued because he was neither present when Cassius Turvey was attacked, nor did his actions directly increase the likelihood of his death, his nine-year sentence was disproportionate.

In contrast, Brearley was sentenced to 22 years in prison and Palmer sentenced to 18 years.

But WA's Court of Appeal today rejected the premise Forth's sentence was "manifestly excessive" and dismissed the appeal.

A panel of three judges ruled Forth's argument effectively ignored his "substantial culpability" for what had happened.

"He joined in, encouraged, and then affirmed by celebration, the pursuit of an unlawful common purpose of chasing children, and terrorising and potentially attacking them, while one of the men was armed with a weapon," the trio wrote in their judgement.

"The children, who had done nothing wrong, were simply walking about after school in the afternoon.

During his trial, the court heard Forth encouraged Brearley to hunt the teenagers they were chasing through the streets of Midvale: "Get them c**ts, Jack."

"It is entirely consistent with your style, Mr Forth, of staying in the background, acting tough, and getting the others to do the dirty work," Chief Justice Peter Quinlan said.

He lambasted his killers as "callous" and "lacking empathy".

However, Justice Quinlan accepted Forth showed "genuine remorse" in a letter he received from him, but said the remorse was "only in its early stages".

Cassius Turvey's mother Mechelle said the appeal process was a "waste of time, a waste of money and resources" that caused her and her family more pain.

She said the appeal had forced them to relive the trauma of losing her son, while accusing Forth of trying to minimise his responsibility for her son's death.

Ms Turvey said she was grateful the appeal court denied his request.