Inmate Arthur Taylor says he's not finished pursuing the jailhouse informants who testified against David Tamihere in a 1990 murder trial.
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"I want the message to get out to these secret witnesses that if you lie in court and you're caught, don't rely on the police to just cover it up, because I might come after you," said Taylor, speaking to Newshub Nation at Waikeria Prison.
Three prison witnesses, referred to as Witnesses A, B and C to protect their identities, told the court Tamihere had confessed to killing Swedish backpackers Sven Urban Hoglin and Heidi Paakonnen in the Coromandel bush in 1989.
Tamihere served 20 years in prison for the murders.
Taylor took a successful private prosecution against Witness C, now known to be convicted double-murderer Roberto Conchie Harris.
He also successfully campaigned for name suppression to be lifted on Witness B, Stephen Kapa, who he also believes lied at trial.
"This guy virtually had a white collar. He must have had a white collar. About five or six people at that particular time in Mt Eden Prison, when he was supposedly there, confessed to this guy," said Taylor. "He took more confessions, as I say, than the average priest."
Kapa died in a road crash in 1995.
Taylor says he's now trying to track down Witness A, who still has name suppression.
"I'm certainly trying to locate where he is. I've got private detectives in Fiji and other places looking for him," he said.
"If we manage to locate him, even if he's overseas, I'll be asking the Government to extradite him, because I believe I've got more than sufficient evidence available to prosecute him."
So why is a serving inmate so concerned about lies told by jailhouse informants?
"I'm pursuing it out of principle to protect the integrity of our criminal justice system, because it's got a bad smell around it now with these secret witnesses.
"If I was here out of my self-interest, don't you think the first prosecution I would've brought would've been against the ratbag that gave secret evidence against me 20-something years ago?" said Taylor.
"If that was my motive… it would have surfaced a lot longer ago when I was involved in crime. I wouldn't have waited until I'd retired from crime."
Taylor says juries don't have all the information they need when considering statements made by jailhouse informants.
"They're not provided with information about the inducements and other things a witness may be acting under," he said.
"You know our old tech term 'garbage in, garbage out'? That's what happens. If the jury doesn't have all the information that they need to make a proper assessment of their credibility, then you can't expect them to."
On this issue, Taylor has an unlikely ally in Justice Minister Andrew Little, who told Newshub Nation he's "pretty uncomfortable" about the use of prison informants.
"We've heard of jailhouse witnesses, particularly when they're giving evidence about so-called confessions, and actually many of them simply haven't stood up.
"If the police insist on bringing witnesses who are current inmates or serving inmates and claim to have heard a confession… the evidence has to include the full circumstances in which that inmate is giving evidence," said Mr Little.
"I think people are entitled to know if a witness is there with the offer of various benefits or things that are good for them…. I think you're entitled to gauge the quality of evidence on that basis."
But, in a statement, a police spokesperson told Newshub Nation: "The motivation for providing information is always considered a factor when police assess the reliability of a statement.
"Evidence from witnesses in prison is considered in the same way as that of other witnesses - police will seek to corroborate the information and consider how it fits in with other evidence in the investigation."
Taylor disagrees: "Let's be quite frank, the police obviously don't like calling them. They're a last resort. You think of the cases that we know they've been called in. The Scott Watson case, for instance, the Stephen Hudson case - all cases where the evidence is weak or there's no bodies, things like that. They're only called as a last resort, so why are the police calling them? Because they need them there to prop up their case."
So where does this all leave Tamihere, who is still a convicted double-murderer on lifetime parole?
Taylor acknowledges that proving a jailhouse informant lied during the trial doesn't mean Tamihere is innocent. But, he says he thinks Tamihere has a good case for a retrial.
"The whole Tamihere case was based on circumstantial evidence - thin strands of a rope. But once those strands start breaking away, the rope's not going to hold up any more, is it?"
"I believe - and as you probably understand, I do know a wee bit about criminal law - that Mr Tamihere now has fresh evidence, ie. the guilty verdict against Harris, eight counts of perjury. Right? Eight counts. Also there is other fresh evidence that is available to him that he can advance," said Taylor.
"That is enough to get, in my humble opinion, a Section 406a application to the Governor-General and ask for a retrial. And he'd be acquitted; I absolutely feel that in my bones."