John Tjepkema doesn't mince words when it comes to his criminal career. It was long. And it was varied.

Key points: More than a third of Australian prisoners are believed to have an acquired brain injury

More than a third of Australian prisoners are believed to have an acquired brain injury Former inmates say they were never asked how they could be assisted with their injuries

Former inmates say they were never asked how they could be assisted with their injuries The Voices for Justice program is teaching former prisoners to advocate for inmates with brain injuries

"I was in the 'revolving door syndrome'," the 60-year-old said.

"I went up the criminal ladder, as I call it. Pinching cars, doing [burglaries], then assaults, then assault and robberies … guns became involved, and drugs … and then armed robbery."

All up, he's spent more than two decades behind bars, starting from the early 1970s. For most of that time he had an acquired brain injury (ABI).

Over the course of his adult life, John has suffered repeated blows to the head, including one knockout so severe all he remembers is coming to three days later.

John's ABI impacted his memory and made it difficult for him to follow instructions in jail and on parole. It's not the cause of his former life of crime, he said. But it did make it harder to break the cycle.

"I tried to explain … in police cells and in prison, you know, I've got something going on and I need some help," he said.

"They just chucked me in the psychiatric unit for several months and just fed me [the antipsychotic drug] Largactil.

"I was like a zombie."

People with ABI make up about 2 per cent of the general population. But they are hugely overrepresented in Australia's prisons.

An audit of Victoria's prisons in 2011 found 42 per cent of male prisoners, and 33 per cent of females, were diagnosed with ABI.

Former inmates Kevin Maloney (left) and Michael Mayne are taking part in the Voices for Justice program. ( ABC News: Peter Drought )

National statistics are similar. In 2018, the Australian Institute of Health and Welfare reported more than a third of prisoners had lost consciousness through a head injury — a leading indicator of ABI.

It is not known how many of these injuries were acquired before prisoners were incarcerated, and how many were acquired in prison.

Now, former prisoners with ABI have come together to tell their stories — and help policymakers understand how the justice system can adapt.

"A lot of people look at [ABI] as a cop-out because they don't understand it," Kevin Maloney said.

"It's not a cop-out."

He is one of the former prisoners who graduated last month from the Voices for Justice program, run by the Centre for Innovative Justice at RMIT University.

The graduates have been trained to be advocates for people with ABI, and to represent their concerns to policy and lawmakers.

"It makes me feel really good to be able to help," Kevin said.

"In the criminal justice system, they don't cater for ABI.

"I've done 20 years jail and never, ever, ever been spoken to about my ABI."

Historically, ABI has not been well recognised by the justice system, according to advocates.

That's partly because it has multiple causes. ABI can stem from traumatic head injuries, stroke, brain infection, and prolonged alcohol or drug use.

'I was in a state of terror'

Dorothy Armstrong's ABI started to develop when she was a teenager. She was one of 11 children and grew up in a violent environment.

She survived numerous incidents of domestic violence before going to prison in 2008.

"I'm a woman, I'm battered — it's obvious, you know I am battered — and it never occurred to anybody that I came into contact with … to ask if I had ever had head injuries," she said.

"'Do you need to have an MRI?' I was never asked. I don't understand that," she said.

Dorothy Armstrong was left with an acquired brain injury after years of domestic abuse. ( ABC News: Norman Hermant )

When she entered prison, her ABI was so severe she couldn't speak. Loss of memory and cognition was a constant behind bars, and once she was released on parole.

"If I didn't respond in a timely fashion or if I wasn't able to have all of my facts correct and in a certain order, assumptions would be made about me as if I was resisting," she said.

"I was in a state of terror every day, terrified that I was going to be sent back to prison if I missed an appointment at corrections."

Dorothy, now 48, was a facilitator for the Voices for Justice program.

Now that it's finished, she and other former prisoners have formed an ABI advocacy group, Voices for Change.

"We are the best people to learn from about the criminal justice system and what does work and what doesn't work," she said.

"It's about the people in power, policymakers, government, knowing the truth of what happens to people like me in the criminal justice system."

Those behind the advocacy group are confident the first-hand experience of former prisoners with ABI will have an impact on policymakers.

"You see their minds change," said the Centre for Innovative Justice's Michael Haralambous, a criminal solicitor who has previously worked with Victoria's Legal Aid and Aboriginal Legal services.

Michael Mayne discusses self-advocacy with fellow former inmate Kevin Maloney (left). ( ABC News: Peter Drought )

"You can see that they suddenly recognise that the numbers, the statistics, the margin for error in their workings [are] human beings. We are talking about human beings."

Group members like Michael Mayne are also convinced this group can make a difference, so prisoners with ABI can escape the "revolving door" justice system.

"Last count I have done about 13 or 14 terms of imprisonment," he said.

"Assaults, armed robberies, gun, a lot of car thefts, a lot of burglaries."

The 51-year old said talking about his experience with an ABI had given him a new focus on the outside.

"I love getting up out of bed of a morning to come here because I am helping," he said.

"I am giving something back to the community."