The United Nations Human Rights Committee says a sex offender with an intellectual disability who has been locked up in psychiatric hospitals and prisons for 45 years should be released and paid compensation.

Photo: RNZ

A child rapist with an intellectual disability who has spent 45 years in mental hospitals and prisons has won a landmark ruling from the United Nations Human Rights Committee that his detention is unlawful.

In a decision sent to the Government two weeks ago and given to the man's lawyer today, the committee said the man - known only as Mr A - should be released from prison and given compensation.

His crimes were abhorrent - a catalogue of child sex offences, which he continued to commit while a patient at various psychiatric hospitals over 26 years and during his single year of freedom in the 1990s.

However, his lawyer, Tony Ellis, said Mr A was a victim too. Sexually abused at the age of six, he was incarcerated in a mental hospital at the age of 12 after being accused of abusing a young girl.

Released at 38, he offended again and has been in prison since.

The UN working group found he has been unlawfully detained since 1994, when his minimum non-parole term ended, and he has been discriminated against because of his intellectual disability.

Dr Ellis said the UN decision was a lifeline for his client, who was now 58, and for other prisoners with intellectual disabilities.

"It's quite a landmark decision, and as the committee found, this is a violation of international law for reasons of discrimination as well as arbitrary detention. It's a major advance for the rights of people with intellectual disabilities."

A spokesperson for the Ministry of Justice said New Zealand took its "international obligations to the United Nations very seriously".

"New Zealand government agencies are looking into the release of this report."

The Department of Corrections, the Health Ministry, the Ministry of Foreign Affairs and Trade and the Attorney General Chris Finlayson have not yet responded to questions from Radio New Zealand.

However, previously the Health Ministry said while it runs five regional facilities which provide secure care for those with intellectual disabilities, people on preventive detention didn't qualify.

Dr Ellis said there were not enough beds for people with intellectual disabilities, and that came down to money.

But he said that was no excuse for arbitrary detention.

The report said in January the committee asked the Government for more detailed information about the man's current situation and the legal basis for his continued detention, but received no response.

Dr Ellis said he was confident the Government would now pay attention.

"It would be somewhat hypocritical of the Government not to comply with one of the UN's principal human rights bodies, especially when it's on the Security Council.

"It would not be a very good look internationally, [it would] just completely destroy your credibility."

Victoria University criminologist Elizabeth Stanley said places on sex offender rehabilitation programmes were very limited and were not set up for people with intellectual disabilities.

She said research done by the Prison Reform Trust in Britain found prisoners with intellectual disabilities faced wider disadvantages in prison. For example, they were more likely to be subject to restraint procedures or placed in segregation.

"This research found that their behaviours are seen to be confrontational and in need of discipline rather than being evidence of their disability. And I think those kind of difficulties, including the difficulties of including them in programmes, mean that they were often excluded from rehab programmes."

Dr Stanley said more research on the experiences and needs of prisoners with intellectual disabilities was needed in New Zealand.

Another human rights lawyer, Michael Bott, said he had several clients with intellectual disabilities, who could not get on rehabilitation programmes and so could never qualify for parole.

"What we're seeing basically is the prisons being used as a default warehouse for people whom the parole board and the Government and the criminal justice system place in the too hard basket.

"And that's just inhumane, it's in breach of international obligations under the International Covenant for Civil and Political Rights, the rights of people who are intellectually disabled and the Universal Declaration of Human Rights."

A spokesperson the Sensible Sentencing Trust, Garth McVicar, agreed people like Mr A and those suffering mental illness should not be in prison.

But he said public safety must come first.

"Let's not forget the victims that he's created and he's likely to create going forward if he's placed back into the community again... It's not our responsibility where they should hold [them], what they should do with him. But it is our responsibility to ensure the public are protected from him."