A man convicted of a double-murder more than 30 years ago, and whose case is back in court, is hopeful the facts will be looked at.

David Tamihere's lawyer will appear at the Court of Appeal in Wellington on Tuesday, where the historical murder case will be revisited.

Tamihere was convicted in 1990 for the murders of Swedish tourists Urban Höglin and Heidi Paakkonen, who were killed the year before.

After his conviction, Tamihere continued to argue for his innocence.

Tamihere told Morning Report he did not know if the Court of Appeal would quash his case this time.

"Things have changed in the legal sense in the last 30 odd years, so I'm just hopeful that they'll look at the facts rather than just being there to protect the system."

Tamihere says the possible outcomes are that the original verdict is upheld, there's a call for a retrial or he could be acquitted. He says he will welcome the opportunity for a full jury trial again.

"It's about time that everything that was wrong with the Crown's case got aired again."

He acknowledges that in his earlier life he did commit some bad crimes.

"My track record certainly didn't help with what happened."

He says since leaving prison, he didn't spend a lot of time thinking about the situation.

"I've always argued if you spend a lot of time brooding on it, you end up in the nuthouse."

Tamihere told Morning Report it's difficult to change people's minds about a case like this.

"When you go to trial you're 80 per cent guilty straight away, because of the fact you are standing in the dock, and then you have to try and change that, and do a 180 on it, whereas the Crown just has to hold their ground."

Criminal barrister Nick Chisnall KC told Morning Report the court will have to decide whether there has been a miscarriage of justice.

"Something that went wrong at the trial, something that went wrong in the first appeal because perhaps it misfired because the court didn't have the full information when it first heard the case, and whether really the safety of the convictions can be upheld."

Chisnall says they can then either order a retrial or the court could quash the convictions.

"Potentially the court could decide that there isn't enough evidence for a retrial, and on that basis quash the convictions and enter an acquittal."

He says the reliance on jailhouse confessions like those used in this case is a real issue for the courts.

"The Crown still relies upon what the researchers show are inherently unreliable witnesses, who are incentivised to lie.

"The reliance put on jailhouse confessions, those in prison who say that they overheard something said by the defendant. It seems to be a significant in many cases that are coming before the courts, and cases like Mr Tamihere's which go back into the 1980s."

No evidence but 'perjury'

Journalist Donna Chisholm has followed the case for years and recently worked with the defence team as an investigator.

She previously worked on another case, and joined the Tamihere team after magazine publisher Bauer closed.

"I'd always harboured very strong doubts about the safety of his conviction," she told Morning Report.

"I joined as a private investigator, which was to try to track people down, find other witnesses doing the same sort of role that you do as a journalist, but only working for his defence team...

"Every single plank of the evidence against Tamihere is gone and it started to erode within months of David being found guilty."

She says the only evidence left linking Tamihere to the murders is "perjury, and I can't see how that can be allowed to stand".

"I hope for justice for David Tamihere, and that would be an acknowledgement that the conviction was unsafe. That would be setting aside his convictions."

A long history

The case was first called into question in 1991 when Höglin's remains were found in Wentworth Valley, 70km from where the Crown said the murders had occurred.

But it was not until 2017 when a secret witness in the case was convicted of perjury that Tamihere started to make headway.

Fellow prisoner Roberto Conchie Harris, previously only known as 'Witness C', was found to have lied about Tamihere confessing to the murder in prison. Harris was convicted of eight counts of perjury and had his identity revealed to the public the following year.

Tamihere criticised the Crown's use of secret witnesses in an interview with Morning Report in 2018.

"These so-called cellmate confessions, no, I don't think you can rely on them," he said at the time. "If there's no corroboratory evidence supporting what these guys have said, you'd have to think long and hard about whether it's prudent to use them."

Tamihere's appeal in 1992 argued that the discovery of Höglin's remains and Harris' false evidence undermined the Crown's case.

Tamihere was granted a royal prerogative of mercy by then Governor-General Dame Patsy Reddy in 2020, paving the way for this week's hearing, expected to run for two days.

-RNZ.