Justin Walker has been in prison in Darwin for over six years without a sentence.

Key points: At least 13 people are in NT prisons because they have been found unfit to stand trial or not guilty by reason of mental impairment

At least 13 people are in NT prisons because they have been found unfit to stand trial or not guilty by reason of mental impairment A criminal lawyer says they are in prison because there is nowhere else for them to go

A criminal lawyer says they are in prison because there is nowhere else for them to go He says some clients plead guilty to avoid indefinite detention

His family is afraid he will not come out alive.

The NT Attorney-General's office is under fire for allowing mentally ill or disabled people to languish inside already overcrowded prisons for years, simply because there are no other places to put them.

The Territory Government's handling of indefinite detention for people with a cognitive, psychiatric or physical impairment often leaves individuals locked up for years with no conviction.

Mr Walker, 36, is one of at least 13 people currently in the custody of the NT Correctional Services Commissioner after being found unfit to stand trial or found not guilty by reason of mental impairment.

Mr Walker's mother Linda Dridi said she was afraid she would never see her son again.

"I don't want my son to be another statistic where a person dies in custody," she said.

"As a mother, I have terrible nightmares."

Criminal Lawyers Association of the Northern Territory president Marty Aust said people who were on custodial supervision orders were almost always housed in the prison because there was nowhere else suitable for them.

"They are not guilty of committing offences, they are vulnerable, they are sick," he said.

"Apart from the fact that these are people living and breathing who are unwell and shouldn't be housed in a prison, the cost of keeping them there is astronomical.

"The way that we judge a society is how we look after those most vulnerable … and in the Northern Territory we should get a big, fat, red F."

Clients plead guilty to avoid indefinite detention

Mr Aust said that there was data to suggest people who were released from prison on non-custodial supervision orders had a low rate of reoffending.

Justin Walker grew up in WA. ( Supplied: Walker family )

"What we seem to find is once people are in the community, their engagement and their life is better … they are able to live a life, reengage and ultimately many of them come off orders all together. They are no longer a risk to anybody," he said.

"But it's not unusual for someone who eventually ends up on a non-custodial order, who was not guilty because they weren't criminally liable for their offence, to spend anywhere between 12 months to three, four or five years in jail before transitioning. Why? Because there is nowhere for them to go.

"This has been recognised by judgements in the Supreme Court by numerous judges, by numerous chief justices, present and former.

"I have lobbied with the Attorney-General, who is also responsible for the Department of Health, which is seemingly a very good dual portfolio because it makes sense, to do something about this."

Mr Aust said it was not uncommon for clients, who may be able to claim a defence of mental impairment, to instead plead guilty to avoid additional years spent in indefinite detention in the Territory.

"We don't need better facilities in the prison, we need better facilities outside the prison so that no person is simply in prison for being sick or mentally unwell or physically or mentally disabled," he said.

Hospitalised following hunger strike

Mr Walker, who is from Western Australia, was diagnosed with schizophrenia at 18 years of age.

He had graduated school and was beginning to embark on a sporting career before illness and injury stopped him in his tracks.

After moving from WA to Darwin to find work, Mr Walker began living in abandoned homes and was indicted for two offences, including arson for attempting to set a house on fire while someone was inside and stealing a wallet and mobile phone.

Since being committed to custody in October 2012, Mr Walker described to his family incidences of physical abuse, solitary confinement and a forced medication regime that was causing adverse side effects.

Mr Walker was rushed to Royal Darwin Hospital late last year after going on a hunger strike.

But neither his mother nor father were contacted by NT correctional services at the time.

"As parents, you think the correctional centre would have made contact to inform us of this situation but unfortunately we didn't get any kind of communication," Ms Dridi said.

"To me, going on a hunger strike is a form of someone wanting to end their life and that is where it became more alarming for us, that he attempted to do this."

His parents also became increasingly concerned when they were told the medication he was being given had started to cause organ damage and weight gain.

"He said to me, 'You know Mum, my body is shutting down and my leg muscles are deteriorating because of the medications that I am having'," Ms Dridi said.

"We don't know the dosage, we don't know anything.

"Everyone has fear and my son, I can sense it in his voice, that yes he has this fear that, is he going to come out of there alive?"

Marty Aust said the NT was failing its vulnerable people. ( ABC News: Bridget Judd )

'He is not a criminal'

Mr Walker's father Arno Tesling said the torment his son had been subjected to would send even a sane person down a dark path and "absolutely destroy a person suffering with mental illness".

"In the middle of last year, in July or August, I received a phone call from a doctor in the Darwin hospital stating that he was in hospital due to a hunger strike, basically he was absolutely lost by this stage," Mr Tesling said.

"He had lost so much weight, his organs were closing down.

"He'd basically had enough. But he came out of that and was put back in the prison system."

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Mr Tesling, who now lives in Queensland, then travelled to Darwin to visit his son.

He said he was told by mental health workers there that the facilities in the NT for mentally ill people were "archaic" and that it would be recommended that Mr Walker be moved to a secure mental health facility closer to family in WA.

"Of course, this has not happened yet," Mr Tesling said.

"My whole thing is Justin, he is not a criminal. He is a mentally ill person who needs care and attention that he just isn't getting in the system that he is in.

"He is getting verbally and physically abused there, which is causing him a great [deal] more trauma and harm to his mental health."

Judicial office 'should be hauled to damning account'

Gerry Georgatos, coordinator of the National Trauma Recovery, has assigned two trauma recovery workers to Mr Walker's case, which will be heard again in the Supreme Court in the coming months.

"Justin's predicament of indefinite detainment at Darwin Correctional Centre, despite his sentence long ago completed, is an indictment of the Office of the Attorney-General," he said.

"The Territory's top judicial office should be hauled to damning account.

"Justin should be immediately released, supported comprehensively with authentic reintegration and all focus on trauma recovery.

"The Attorney-General's Office must be obligated to an immediate inquiry of how many others like Justin are incarcerated who should not be."

Attorney-General Natasha Fyles declined multiple interview requests but issued a statement saying that there was "an increasing number of Territorians who are found unfit to plead".

"As Attorney-General and Minister for Health, I have my departments working together to deliver best practice policies and treatment," she said.

"Significant work is already underway to assess current resources, future resourcing needs and potential statutory and other reforms that may be required."