Rapist Mark Chisnall, who lives inside prison gates despite no longer serving sentence, seeks release

The Court of Appeal building in Wellington. Photo / Mark Mitchell

Lawyers for a serial sexual offender who has spent years at a lockdown residential facility on the grounds of Christchurch Men's Prison - despite having completed his sentence in 2016 - have argued again to the Court of Appeal that his situation is unjust.

Mark David Chisnall has spent much of his adult life in prison, having committed his first rape when he was 14. His convictions include the rapes of an 8-year-old girl and a woman in her 20s, as well as sexual assaults of a 7-year-old boy and a 20-year-old woman.

His 11 years in prison included reports of continuing aggressive behaviour and sexual fixations, authorities have previously said.

Corrections applied to the High Court at Auckland in 2016 for a rare public protection order (PPO), which allows for those considered a "high risk of imminent serious sexual or violent offending" to be indefinitely held at a secure facility.

Chisnall now has more freedoms than traditional prisoners - for instance, he has a PlayStation and his own toilet - but his residential facility remains inside the prison's perimeter fence.

"A PPO is a draconian and an arbitrary detention of the worst possible kind," lawyer Tony Ellis told Court of Appeal justices today during a six-hour hearing held over audio-visual link. "Certainly Mr Chisnall is not one of the most dangerous criminals in the country, which was the purpose of constructing this regime."

He described his client as having multiple intellectual and psychological disabilities and described public protection orders as having become a "dumping ground for people who are intellectually challenged ... because there's nowhere else for them to go".

Justice Patricia Courtney, who heard the case alongside Justices Denis Clifford and Murray Gilbert, took issue with the statement.

"Merely being intellectually challenged is not the problem here," she said. "Most intellectually challenged people don't rape."

Chisnall's lawyers said they want to see the court quash the PPO, but they would be amenable if the High Court was directed to order a less restrictive extended supervision order (ESO) with intense supervision for 12 months.

With an ESO, Chisnall could stay at a residential facility outside prison fences - albeit perhaps with an electronic ankle bracelet.

If he doesn't make progress after 12 months on an ESO a new application can be made for a PPO, lawyer Graeme Edgeler noted. It would allow his client to work towards his goal of getting a job, he said.

"He wants something to do with his day," Edgeler said, explaining that Chisnall has considered mowing lawns for a living if given enough freedom to do so. "In our submission, Mr Chisnall should get a chance [to prove himself on electronic monitoring]."

Up until a year ago, trips outside the prison's perimeter fence were rare - for medical appointments only. But the PPO facility has changed the way it operates over the past year, with more of an emphasis on rehabilitation and reintegration, the justices were told today.

As a result, Chisnall has had over 100 supervised visits outside the gates in the past year with no reported incidents, the justices noted.

But Matthew McKillop, a lawyer for Corrections, pointed out that the latest 12-month review in December found that Chisnall still poses "the same very high risk of serious sexual offending".

While he has done well under the strict regimen of his current placement, he poses more of a risk in a "less protectable place", McKillop said, directing the justices also to a report that suggested Chisnall continues to have violent sexual fantasies roughly every four months as a way of coping when especially angry.

"It's not been 100 per cent plain sailing," McKillop said, adding that a less restrictive facility would be more likely to trigger Chisnall's offending behaviour.

"The wire is the ultimate backup," he said.

The justices reserved their decision.