When police bungled the investigation into the killing of her 21-year-old son, Ingrid Bishop was furious.

That fury has now turned to fear — that the wrong man is behind bars, while the dysfunctional system that put him there remains unchanged.

Key points: Woman calling for inquest into son's death fears man who confessed to murder without interpreter present is innocent

Woman calling for inquest into son's death fears man who confessed to murder without interpreter present is innocent WA Chief Justice cites link between access to interpreters and number of Aboriginal people in jail

WA Chief Justice cites link between access to interpreters and number of Aboriginal people in jail Kimberley Interpreting Service says English words often misinterpreted in Aboriginal context

"To think that there's an innocent person in jail is absolutely tragic," Ms Bishop said.

"It's as if 'OK someone is in jail, that's good, we've done our job' and off they go.

"All the institutions, the departments, the bureaucrats, everyone who is there to actually support the process have just completely turned their back on this."

Joshua Warneke was found dead on the side of the road in Broome in 2010.

Two years later, Gene Gibson — a 21-year-old illiterate Aboriginal man from a remote community — was charged with murder after he made admissions about the crime to police.

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The confessions were made during a nine-hour interview with police, without an interpreter or a lawyer, despite Gibson's limited understanding of English.

The evidence was thrown out of court after a judge found police had denied Gibson many basic rights and he later pleaded guilty to the lesser charge of manslaughter.

In handing down his reasons, Justice Stephen Hall said it was clear an interpreter was needed and there was no excuse for not obtaining one.

"There is a significant possibility that answers given by the accused are unreliable because he did not understand what he was being asked, could not communicate his own thoughts adequately in English or gave false answers in order to appear agreeable," Justice Hall said at the time.

"In my view it is unlikely that the admissions of the accused would have been made at all if the interview had been properly conducted."

The WA police officers involved in that case are now being investigated by the Corruption and Crime Commission, and Ms Bishop said she believed her family was paying the price.

"The consequences of not having an interpreter are catastrophic, it has had a profound effect on the justice for Josh — we won't get that," she said.

Ms Bishop is calling for a coronial inquest into her son's death, believing it is her last chance for answers.

Not an isolated problem, says WA Chief Justice

WA's Chief Justice Wayne Martin said it was not an isolated problem and the lack of interpreters affected all stages of the criminal justice system.

He said innocent people may be sent to prison as a result.

"If the accused person does not understand the language in which the case is being conducted, then the process is invalid, it's ineffective and it's a nullity," he said.

"Now we have reason to believe that there are a number of those cases that are occurring regularly in Western Australia because we simply lack the capacity to identify the people who need the interpreters or to provide the interpreters when they are required."

WA Chief Justice Wayne Martin said there was no overnight solution, and is calling for better training to identify when an interpreter is needed. ( ABC News: Courtney Bembridge )

Chief Justice Martin said there was an "obvious and direct link" between access to interpreter services and the number of Aboriginal people in prisons.

"There is a sector of the West Australian community — being the original inhabitants of this state — who lack the resources they need to fairly and efficiently negotiate the justice system," he said.

"Instead of additional resources being provided in this area, the amount of resources that we're providing has been reduced."

WA has the nation's highest over-representation of Indigenous people in jail — with an imprisonment rate 18 times that of non-Aboriginal adults.

But the state is not alone.

"The areas that are most affected by this problem are in the remote parts of Western Australia, South Australia, Northern Territory and Queensland," Chief Justice Martin said.

Amnesty International said it was an injustice that needed to be rectified.

"There was one example of a man who went through an entire first degree murder trial in the Northern Territory using his two words, yes and good, and it wasn't until the end of the trial that they realised he was clinically deaf," Indigenous Peoples' Rights campaigner Tammy Solonec said.

"It has been a big problem for a long, long time. In 1991 there was a parliamentary inquiry which found it was a grave injustice against Aboriginal people. Here we are 24 years later and they still haven't resolved the issue."

English often misinterpreted in Aboriginal context

The WA Government withdrew its funding for the state's only Aboriginal interpreting service, the Kimberley Interpreting Service (KIS), last year.

KIS said federal funding had kept it running with skeleton staff but the service needed four times that amount to do its job properly.

"The current funding that we have is not enough to provide the service that we need to for the people who are at a severe disadvantage because they don't understand," chief executive Deanne Lightfoot said.

Ms Lightfoot said there were more than two dozen Aboriginal languages spoken in the Kimberley region alone, with many people speaking a different version of English.

"English words are quite often misinterpreted when they're spoken in an Aboriginal English context, so somebody may hear the words kill and assume it means kill dead when in fact it can just mean to harm somebody," she said.

"Somebody may hear the words rape — it can just mean to have consensual sex.

"What we see is people assuming that they're understanding, they're hearing English words, they're assuming that there's clear communication there but in fact there's not, there's absolutely not and we see dire consequences because of that — it happens every day."

The Chief Justice said there was no overnight solution.

He has called for better training to help police and court staff identify when an interpreter is needed, and more funding for interpreting services to ensure that need can be met.