Teina Pora is poised to ask the Privy Council to quash his convictions for a controversial 1992 rape and murder.
His team is understood to be preparing to seek leave from the Court of Appeal to take an appeal to the top British court, putting on hold his application for the Royal Prerogative of Mercy whereby the Governor-General can refer a case back to the New Zealand courts.
"In the process of investigating the prerogative application we have amassed evidence which makes us believe an application directly to the court to go to the Privy Council is (warranted)," Pora's lawyer Jonathan Krebs said.
"We have even more evidence than we expected we would get that supports Teina's position," Mr Krebs said.
The Supreme Court became New Zealand's top appeal court in 2004 but cases heard by the Court of Appeal before then can be referred to the British court.
Pora has twice been convicted of raping and murdering Susan Burdett. The 39-year-old accounts clerk was bashed in her Papatoetoe home in 1992.
Pora was convicted in 1994 and again found guilty at a retrial in 2000, ordered after the semen in Ms Burdett's body was found to match the DNA of Malcolm Rewa, the country's second-most prolific rapist and someone who otherwise always attacked alone.
Rewa was eventually convicted of Burdett's rape, but two juries couldn't decide about murder.
New evidence includes the opinion of a world authority on false confessions that Pora's confessions are "fundamentally flawed and unsafe" and a British criminal profiling expert who says it is "highly unlikely" Rewa would have worked with any co-offender let alone Pora, 23 years younger and a juvenile associate of a rival gang.
Pora was 16 when arrested and has been in jail for 20 years. His convictions were based on his contradictory statements and testimony by witnesses, at least three of whom were paid by police.
In a documentary to screen tomorrow on Maori Television, veteran barrister Marie Dyhrberg reveals that of all her cases she believes most strongly that Pora is innocent.
When she first saw him, soon after he was charged, he'd seemed stunned and bewildered. Hunched over and crying, he'd said, "I wasn't even there."
The Confessions of Prisoner T, Maori Television, Sunday 8.30pm.