Testimony from a notorious jail house snitch should never have been put to the jury in David Tamihere's first double murder trial, the Court of Appeal has been told.
Tamihere was convicted in 1990 for the murders of Swedish tourists Urban Höglin and Heidi Paakkonen, who were killed the year before.
He was granted a rare Royal Prerogative of Mercy in 2020, which triggered an appeal hearing on Tuesday and Wednesday in Wellington.
Today, Tamihere's lawyer James Carruthers told the court false evidence undermined the Crown's case.
That evidence came from Roberto Conchie Harris - who said Tamihere confessed to the murders.
He was prosecuted in 2017 and found guilty of perjury in relation to his evidence.
Carruthers said the evidence should never have been put to the jury. Two trampers claimed at Tamihere's original trial they saw Tamihere with Paakkonen at Crosby's Close where the Crown alleged the murders occurred.
"You can draw a link to who was at Crosby's Close, you can then draw a link to the trampers' identification evidence. These are just some of the lines of reasoning available to the jury using Mr Harris' evidence in conjunction with other evidence in the case. And none of them should have been available".
He said prisoner informer evidence was given a lot of weight by juries.
"It's one of the most problematic categories of evidence out there, along with eyewitness identification evidence. There is a real risk that if the door is left ajar, the jury will push it over and walk through."
The lawyer then moved on to the discovery of Urban Hoglin's body 70km away from the alleged murder site.
Carruthers argued it was impossible Tamihere could have disposed of the body there the same afternoon he was allegedly seen with Paakkonen by the trampers.
He was asked about the inconsistencies in Tamihere's account of his movements that day and whether he was trying to distract police from where the body was.
"Well no, the significance didn't just arise then. His movements were a key issue at trial. He had himself elsewhere than where the Crown wanted him."
However, the Crown argued the questions over movements and timings were not a problem for this panel of judges.
"There was no suggestion in 1992 [when the Court of Appeal first rejected Tamihere's appeal] that these matters posed a problem for the Crown case and in my submission, it's not a problem now."
The judges asked the defence to be clear about the evidence they contest.
Justice Miller said at this stage it was clear there has been miscarriage of justice due to the perjured evidence by the inmate.
"The question we then have to answer is whether we ourselves are satisfied that the evidence proved his guilt beyond reasonable doubt."
Tamihere did not attend the hearing on Tuesday but he told Morning Report the possible outcomes were that the original verdict was upheld, there was a call for a retrial or he could be acquitted.
He hopes the case goes to another jury trial.
"It's about time that everything that was wrong with the Crown's case got heard again. You can't just keep making up different versions."
The hearing continues at the Court of Appeal on Wednesday.