A secret jailhouse witness, whose evidence was a key component in the double-murder trial of David Tamihere, has been found guilty of perjury.

The verdict shocked many in the courtroom, and has been described by Tamihere himself as a "major" moment in his case. He has always professed his innocence.

The identity of Witness C remains suppressed, but his testimony in 1990 was "powerful" and led to Tamihere's guilty verdict for killing Swedish tourists Urban Hoglin and Heidi Paakkonen.

The prison informant was on trial this week in the High Court at Auckland after being charged with perjury and attempting to pervert the course of justice for what he said on the stand and for a sworn affidavit recanting his testimony in 1995.

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The jury returned guilty verdicts on eight perjury charges after nearly a day of deliberations, which began yesterday afternoon.

Witness C was found not guilty of obstructing the course of justice, which pertained to the affidavit.

He appeared to show little emotion in the dock when the verdicts were read.

Tamihere was also in court for the moment.

Urban Hoglin, 23, and Heidi Paakkonen, 21, disappeared during April 1989 in the Coromandel Ranges. Photo / File
Urban Hoglin, 23, and Heidi Paakkonen, 21, disappeared during April 1989 in the Coromandel Ranges. Photo / File

Afterwards, a pleased and almost overwhelmed Tamihere, said the verdict was a "major" for himself and the whole concept of secret witnesses.

"I'm still under life parole, it's a hell of a long haul to go yet," he said of trying to prove his innocence.

"This verdict has changed the argument that the Crown have been using and the Court of Appeal has used, the whole axis changes, that's what I say.

"The affidavit is a moot point really, the main thing was the perjury."

Tamihere's murder convictions stand as he has already exhausted the judicial appeals process after he was denied leave to appeal to the Privy Council in 1994.

Witness C was remanded in custody until sentencing on October 6.

David Tamihere being escorted by prison guards during his trial in 1990. Photo / File
David Tamihere being escorted by prison guards during his trial in 1990. Photo / File

Witness C's former prison inmate and "jailhouse lawyer" Arthur Taylor, who laid the private prosecution, said that he brought forward the case to "send a loud, clear message to jailhouse snitches".

"If the police, on behalf of whom they gave false evidence, won't bring them to justice - then if I get sufficient evidence - I will," he said in a recorded message to the Herald.

"I've had a gutsful . . . They always appear in cases where the police have very little or no reliable evidence."

Taylor said any jury verdict resulted on false evidence is "obviously not sound".

"David Tamihere, after waiting over 28 years, has finally received some justice," he said.

Taylor thanked prosecutor Murray Gibson, and researchers Mike and Jenny Kalaugher.

"We've had to do the job of the police here. The job that the police are resourced and paid to do," he said.

Witness C was one of three secret witnesses who gave evidence for the Crown during Tamihere's trial.

Researcher Mike Kalaugher and David Tamihere at the High Court in Auckland. Photo / Jason Oxenham
Researcher Mike Kalaugher and David Tamihere at the High Court in Auckland. Photo / Jason Oxenham

In his 1990 evidence, Witness C said Tamihere told him in a cell confession that he killed the Swedes. Tamihere has always said the conversation never took place.

The secret witness told the court this week that he was "disgusted" at how Tamihere boasted of the killings.

Hoglin, 23, and Paakkonen, 21, disappeared in April 1989 after leaving their car at the end of the Tararu Stream road in the Coromandel Ranges.

Tamihere admitted stealing the Swedes' car but denied having met them.

He was convicted of the murders and eventually released from prison in 2010 after serving 20 years.

Hoglin's remains were discovered by pig hunters in 1991 in bush near Whangamata, about 70km from where the murders were alleged to have taken place.

A pathologist also concluded that Hoglin did not die from a blow to the head with a "lump of wood", as Witness C had testified.

The discovery of Hoglin's body showed certain evidence was "patently wrong", such as the bodies being disposed of at sea, Gibson said yesterday in his closing submissions.

Paakkonen's remains have never been found.

Gibson said Witness C had a "vivid and sordid imagination".

He said the informant had got "many items of his evidence horribly wrong", but nonetheless it was "powerful" for the jury during the 1990 trial.

In 1995, Witness C swore an affidavit stating that he lied and gave false evidence after police offered him "major inducements", including $100,000.

He later confirmed the legal document in a nationally televised interview with the late Sir Paul Holmes in 1996.

However, he recanted his affidavit just weeks after the Holmes interview.

Then in June 2007, Witness C wrote a letter to Tamihere which read that the "trial evidence was all false and fabricated by the police anyway".

However, Witness C then said the three separate admissions that his testimony was false were made while he and his family were under threats from fellow prisoners because of his reputation as a prison "nark".

"It was a difficult situation to be in, it was a dangerous situation to be in," Witness C told the court this week.

"I was too busy trying to stay alive - I didn't worry about the contents of the statement," he said.

"There was only one thing on my mind at that particular time, that was keeping myself and my family safe."