A Dunedin cleaner found guilty of beating his boss to death with a hammer wants his conviction quashed because his autism was not raised at trial.

Alexander James William Merritt, 23, was jailed for life for the murder of 51-year-old Karin Ann Ross, and Justice Nicholas Davidson imposed a minimum non-parole period of 12 years. He called it a "sudden, violent and callous" attack, which took place in the car park of Spotless Cleaning Services early on December 2, 2015.

It was revealed at sentencing that Merritt had autism spectrum disorder (ASD) — an issue that was discovered before trial but not raised with the jury which found him guilty.

Counsel Tony Ellis told the Court of Appeal this week that there was a miscarriage of justice as a result.

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ASD threw into question whether Merritt could have formed the required "mens rea" (intention or knowledge of wrongdoing) to be found guilty of the crime, he suggested.

While Ellis had no psychiatrist's report to confirm that, he provided references to numerous experts and overseas legal authorities about the disorder.

Counsel Anne Stevens, who represented Merritt at trial, said she had not been instructed to pursue an autism-based defence by her client.

"Mr Merritt's instructions were to defend the charge on the basis there was insufficient evidence that he killed her," she wrote in an affidavit.

Stevens added that she had no concerns about his intellectual capacity.

"Alexander Merritt may appear indifferent and lacking engagement, whereas I quickly found out he was quite a deep thinker," she said.

Ross' father Maurice Boyles told the Otago Daily Times he was aware of the appeal but refused to be drawn on its specifics.

"It's an ongoing saga," he said.

"It's bad because it keeps coming back all the time. I just want it over and finished with," Boyles said.

Merritt was slammed by Justice Davidson for his "remarkably cold-blooded indifference" which came through in his behaviour after Ross' death, particularly in an interview with police.

The defendant told Detective Graeme Smaill he did not care the woman was dead and admitted making numerous violent threats behind her back.

"This no doubt goes to the somewhat obvious thinking of the judge that Mr Merritt has maliciously killed the deceased — no doubt the jury also considered he had psychopathic traits as well, no autism explanation being given as to his behaviour," Ellis said.

Outside the context of ASD, he said, Merritt came across as heartless and cold.

Had there been information aired about his disorder at the start of the trial, rather than at sentencing, "a manslaughter verdict may have been possible", he told the court.

The appeal coincided with the unveiling of a new online resource for the legal community assisting with vulnerable witnesses and defendants.

"Benchmark" — a project centred at Dunedin's Donald Beasley Institute — consulted people with intellectual disabilities and 40 judges about their experiences with the court.

Team member and AUT Professor of health law Kate Diesfeld said some of the interviewees' stories were "harrowing".

"People with ASD are particularly vulnerable in my estimation. Their response in that [court] setting may be viewed as cold, indifferent, [and] lacking in remorse but that's not necessarily an accurate portrayal of the emotions they experience," she said.

So if someone's disorder was disregarded through the court process, could that lead to unfair trials and unsafe verdicts?

"Perhaps," Prof Diesfeld said.

The Court of Appeal's decision is expected next month.

If the appeal failed, Ellis said an appeal against the length of Merritt's sentence would be likely.

The Merritt family refused to comment.