David Tamihere's double-murder case is heading back to the Court of Appeal, Justice Minister Andrew Little says.
It follows acceptance by the Governor General of advice from Little last year on a Royal Prerogative of Mercy application made by Tamihere.
Tamihere spent nearly 20 years in prison after being found guilty in 1990 of murdering Swedish backpackers Urban Hoglin, 23, and Heidi Paakkonen, 21, in the Coromandel.
He has always professed his innocence.
Tamihere had skipped bail for a 1986 rape and was on the run when the murders were committed. The brother of former Labour Cabinet Minister John Tamihere also has a manslaughter conviction for the 1972 death of an Auckland prostitute.
The mystery over whether he was the Swedes' killer gripped the nation and sparked the biggest land-based search ever undertaken in New Zealand, but no bodies were initially found.
Little said he made the rare legal announcement today after considering Ministry of Justice advice, assisted by a retired High Court judge.
Cabinet this week completed the administrative process required to send the case back to court, Little said, which had been delayed due to the Government's response to Covid-19.
"I advised Her Excellency to refer Mr Tamihere's convictions back to the Court of Appeal for further consideration," Little said.
"As the matter will shortly come before the Courts, I will not be making any further comment."
The case will be heard by the court as a further appeal, Little said.
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Little's announcement comes after a police informant at Tamihere's 1990 trial was found guilty of perjury following a 2017 trial in Auckland.
Former inmate and "jailhouse lawyer" Arthur Taylor's private prosecution of the prison snitch, who was known for decades only as Witness C, uncovered a string of lies and suspect police work.
Witness C was one of three prisoners which the Crown relied on at Tamihere's trial to give what was described as "powerful" evidence.
The prisoners all claimed Tamihere had, at different times and while in custody, confessed to how he sexually assaulted and killed the Swedes.
The 2017 jury decided Witness C was guilty on eight perjury charges but not guilty of obstructing the course of justice, which pertained to his 1995 affidavit recanting his murder trial testimony.
After he was sentenced to eight years and seven months' imprisonment for his courtroom lies, a lengthy suppression battle ensued before Witness C was finally unmasked in April 2018 by the Herald and other media as Roberto Conchie Harris - a double murderer, sex offender and fraudster.
Tamihere has told the Herald that Witness C's perjury convictions were a "major" moment in his case, while a High Court judge said the snitch's lies were a "brazen assault on the foundation of our criminal justice system".
At the 1990 trial, Harris had testified that Tamihere confessed to him while they shared a prison cell.
Harris was serving time for killing Northland couple Carole Anne Pye and Trevor Martin Crossley when Tamihere was arrested for the Swedes' murders.
He told the jury Tamihere attacked and sexually assaulted the backpackers before dumping their bodies at sea.
But in 1991, Hoglin's remains were discovered in bush near Whangamata, about 70km from where the murders were said to have taken place.
Paakkonen's remains have never been found.
In 2018, the Herald also unmasked another Tamihere informant, Witness B, as the late Stephen Kapa, who died in a car crash in February 1995.
Witness A, a convicted killer and drug supplier, is the only one of the three snitches to still enjoy the suppression of his identity from Tamihere's trial.
However, his exact location and wellbeing remains unknown despite speculation the informant may now be overseas, possibly in Fiji.
1989: Paakkonen and Hoglin disappear on the Coromandel Peninsula
1990: Tamihere is convicted of murdering the Swedish travellers and sentenced to life imprisonment
1991: Hoglin's remains are found near Whangamata
1992: The Court of Appeal rejects Tamihere's appeal
1994: Tamihere denied leave to appeal to the Privy Council
1995: Witness C swears an affidavit retracting his evidence
1996: Witness C retracts his retraction
2010: Tamihere is released on parole
2016: A private prosecution alleges Witness C lied at Tamihere's trial
2017: Witness C appeals the perjury convictions and sentence and fights to keep his identity hidden
2018: Witness C drops his appeal against the perjury convictions and is later revealed as Roberto Conchie Harris
2020: Justice Minister Andrew Little announces David Tamihere's case is heading back to the Court of Appeal after a Royal Prerogative of Mercy application