Alfred Thomas Vincent was one of the first people to be sentenced to preventive detention in 1968 after he was convicted of indecently assaulting five boys aged 12-14.
He has spent more than 50 years in prison, and was again denied parole in August last year following "continued poor conduct" behind bars.
Vincent, now 83, has deteriorated mentally and physically, and the parole board found releasing him held "significant dangers" due to his sexualised conduct.
The only time Vincent has spent outside the razor wire was during day passes and weekend leaves in the early 80s - which were revoked when he was caught talking to young boys.
But now Justice Jillian Mallon in the High Court at Wellington has ordered he be released, finding he was being detained "arbitrarily" in breach of the Bill of Rights Act.
In her judgment, published today, Justice Mallon said Vincent had stage five dementia and did not appear to know his own name. He cannot speak clearly or care for himself.
"He has been refused parole at least 48 times, most recently on 19 August 2019," she said in her judgment.
"He is apparently New Zealand's longest-serving prisoner. How can this be?
"I consider the process which ought to have enabled his release some time ago has miscarried. He no longer represents an undue risk to the safety of the community."
Psychological reports over the years continued to assess Vincent as being at a high risk of reoffending against children, but not against adults.
In recent years he has suffered significant cognitive decline, to the point where he cannot recall his own age, has trouble naming simple objects, and often mixed up night and day.
In the latest parole decision, the board said if Vincent were to be put in a psychogeriatric care facility, the staff might need to be trained to manage his sexualised behaviour, and that no such facility was currently available.
In July this year, Vincent's lawyer made an application for compassionate release, expressing concern that little seemed to have been done to advance a release plan for Vincent despite a 2007 Parole Board decision stating that it was "unacceptable to think that he is doomed to die in prison".
The prison director provided a report last August stating Vincent had little understanding of where he was and why he was there, but was easy to deal with and could generally be lured back to his cell with tea and a biscuit.
"Vincent is generally quiet and smiley, with little understanding of his surroundings," the director said.
His "disinhibited behaviours" were easily managed with distractions and directions.
The application was refused because no suitable secure care facility could be found for Vincent.
The matter eventually came to a judicial review before Justice Mallon, with Vincent's counsel alleging the Parole Board had erred in multiple areas, including failing to take into account his mental impairment and the Bill of Rights Act.
Counsel argued the board incorrectly factored in Vincent's sexualised conduct in prison, when that conduct was actually a symptom of his dementia, and was lawful.
Another doctor report from October this year found he was "mentally totally incompetent" and "dependent on carers for every aspect of his living".
The doctor said he "cannot pose a risk to any person" and needed appropriate care.
Justice Mallon said the punitive part of Vincent's sentence finished more than 40 years ago, and that the need for public protection must be "compelling" if Vincent was to be detained for such a long time.
She believed the board was wrong to find Vincent was a risk to the community.
"How realistic was it that, as an elderly man with dementia, who was easily redirected and managed, he would have the opportunity to sexually offend against young boys or indeed anyone?
"The board appears to have equated continued interest in sexual activity as equating with risk, and risk as equating with an undue risk, without more consideration."
Justice Mallon made a declaration that Vincent was being arbitrarily detained in breach of the Bill of Rights Act.
She set aside the August 2019 Parole Board decision and made an order for him to be released from jail. The order is delayed for three months so the Crown can find an appropriate facility for Vincent.
