A judge has dismissed indecent assault charges against a man, accepting he was sleepwalking at the time after getting drunk.

The Herald on Sunday can finally reveal the story of Tristan Corey Scott after fighting his application for permanent name suppression.

It is the fifth known case where sleepwalking or parasomnia has been used as a defence in a New Zealand court and it is cropping up more around the world.

But the mother of the two teenage girls who were indecently assaulted in the latest case told the Herald on Sunday the verdict was "atrocious".

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Read more: The science of sexomnia

The teenage girls, who were sleeping in separate bedrooms, gave evidence that they awoke to find Scott in their rooms, touching their legs, according to court documents.

He and his partner had spent the night socialising with the parents of the complainants at their home.

The court heard that Scott, who lives in Wellington and works in IT, had been drinking heavily.

Scott, 35, has a previous indecent assault conviction from 2011 after pleading guilty to molesting a woman who was also asleep in her bed. He had been drinking alcohol prior to the incident.

This and a third alleged instance that did not result in charges, in which Scott entered a darkened house uninvited, were cited by police as showing a propensity to enter rooms where women were sleeping.

But Scott's lawyer argued that the earlier incidents could be other examples of parasomnia.

Expert evidence about the condition was given by a sleep specialist who Scott had approached for treatment.

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District Court judge Jim Large found that the girls were indecently assaulted by Scott, but dismissed the charges saying he was not conscious of what he was doing because he was in a state of automatism by way of parasomnia, caused by excessive drinking.

Automatism is a legal term meaning the performance of actions without conscious thought or intention.

Parasomnias are a group of sleep disorders of which sexomnia is one. Sometimes called sleep sex, sexomnia is similar to sleepwalking but causes people to engage in sex acts.

The judge said he found the complainants to be reliable witnesses and was sure that Scott committed the acts they described.

But the teenagers' mother does not believe that Scott suffered an episode of parasomnia, which meant he was incapable of knowing what he was doing.

"For me, he just got drunk to the point he did things he shouldn't have."

Her daughters were disappointed, she said.

"Considering the process, it was a lot to go through at a young age. This November will be three years since this happened.

"For them to see this guy can just walk away without anything, they are pretty bummed out about that."

Police told the girls' mother that the prosecutor took issue with aspects of the decision relating to parasomnia and wanted to appeal to the High Court but following a review by the Deputy Solicitor General this did not proceed.

Scott can be named following a decision in May by Judge Large dismissing Scott's application for permanent name suppression. Scott did not seek name suppression during the trial but did so after the Herald on Sunday approached the court for information.

Scott did not respond to requests for comment.