An Aboriginal man with cognitive impairment has walked free from jail after almost five years behind bars, with WA's highest court overturning his conviction for the bashing death of Josh Warneke outside Broome.

Key points: Gene Gibson was jailed in 2014 after pleading guilty to the manslaughter of apprentice carpenter Josh Warneke

Gene Gibson was jailed in 2014 after pleading guilty to the manslaughter of apprentice carpenter Josh Warneke Warneke's body was found with head injuries on the side of the road on the outskirts of Broome

Warneke's body was found with head injuries on the side of the road on the outskirts of Broome Today the Court of Appeal overturned Gibson's conviction, after it heard his own lawyer told him to plead guilty and he did not understand court processes

Gene Gibson, from the Western Desert community of Kiwirrkurra, had pleaded guilty to the manslaughter of Mr Warneke, who was found dead on the side of a road after leaving a nightclub in February 2010.

However, Mr Gibson's conviction was set aside in a unanimous decision by the Court of Appeal.

He was released from Casuarina Prison near Perth just before 11:30am.

Mr Gibson, 25, was sentenced in 2014 to seven-and-a-half years in jail after admitting the unlawful killing of Mr Warneke, 21.

Josh Warneke's body was found by the side of Old Broome Road in 2010.

But Mr Gibson — who speaks limited English and whose first language is the traditional desert language of Pintupi — argued he did not understand the court process or the instructions given to him through an interpreter when he entered his plea.

Mr Gibson was convicted of manslaughter in 2014. ( Supplied: Desert Feet Inc )

Testifying at the appeal earlier this month, he told the court via an interpreter that he did not kill Mr Warneke and said police had not listened to his story.

The court also heard he was advised to plead guilty after he was implicated in witness statements — and it was not until after he had done so that two incriminating witnesses recanted their evidence.

Expert witnesses said Mr Gibson's limited English was compounded by mental impairment.

The court is yet to publish its reasons for throwing out the conviction.

Gibson innocent, Josh Warneke's mum says

Mr Warneke's mother Ingrid Bishop welcomed the verdict and described it as a "great day as it's the beginning of the next stage of Gene Gibson's life".

Ingrid Bishop (right) joined Gene Gibson's family, including his mother Alamay (second from right), during the appeal. ( Supplied: Ingrid Bishop )

"I am so happy for Gene and his family ... to see him walk free is one of the most profound moments of my life," she said.

"As I have said over the past several years, Gene is innocent.

"The appeal process has highlighted numerous deficiencies and incompetence in how Aboriginal Legal Services managed Gene's case.

"The very agency tasked with protecting and supporting Gene, failed, and failed dismally and has taken the process of justice back 50 years for Aboriginal Australians.

"There must be consequences for this as Gene and his family have borne the full impact of this failure."

In a statement, Aboriginal Leagal Service of WA (ALSWA) CEO Dennis Egginton said police should take full responsibility for Mr Gibson being jailed.

"It was the Aboriginal Legal Service which originally fought for Mr Gibson in exposing the police investigation which resulted in his confession being thrown out," he said.

"A subsequent CCC report confirmed beyond a shadow of a doubt that police must take sole responsibility for Mr Gibson's conviction and imprisonment.

"I can't begin to imagine how traumatic these past few years have been for Mr Gibson, his family and the family of Mr Warneke.

"But the fact remains, that the conduct of police from the moment they decided Mr Gibson was a suspect in the death ensured that a miscarriage was certain to occur."

Mr Egginton also said that ALSWA stands by its former lawyer, Dominc Brunello.

"Dominic is an exceptional lawyer whose representation of Mr Gibson was as good as any lawyer in WA could provide and at all times, Dominic acted with professionalism and in the best interests of Mr Gibson," Mr Egginton said.

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Mr Gibson's lawyer Michael Lundberg also welcomed the ruling.

"Gene is, of course, very happy with today's decision," he said.

"It's important to note that there are no winners in this matter, though. Gene has been in custody since he was arrested ... he's been away from his country for a long time and is very keen to return and be with his family.

"There is also the reality that the life of another young man, Josh Warneke, came to an end in Broome seven years ago.

"Josh and Gene have never met, but their lives are now intertwined.

"We wish to acknowledge in that regard Josh's mother, Ingrid Bishop, who has publicly supported our client's cause, and we hope in the future she obtains the justice she and her family deserve."

A roadside memorial marks the spot where Josh Warneke's body was found. ( ABC Kimberley: Ben Collins )

Ms Gibson said her family was looking forward to the case being reopened with a fresh start.

Mr Gibson was originally charged with murder in August 2012, but it was downgraded after police were found to have bungled a police interview.

A Corruption and Crime Commission (CCC) investigation into the death of Mr Warneke later exposed "systemic failures" within WA Police.

It focussed in particular on what it called a "series of flawed police interviews" with Mr Gibson in 2012, saying detectives ignored local officers' advice to redo their interview and arrange an interpreter.

Kimberley Interpreting Services chief executive Dee Lightfoot said the case has led to an increase in police using interpreters.

"We have noticed a great change [in the use of interpreters], we've had 60 engagements this year which is more than we've ever had by the police," she said.

"People are entitled to interpreters the whole way through their trail of justice, with police, with lawyers, with court, and that's not only for the accused its also for witnesses.

"It was avoidable, it was absolutely avoidable, they [the police] just needed to make one phone call."

Ms Lightfoot said they were starting conversations with the Government about improving the availability of interpreting services.