A jury is now deliberating on whether a secret jailhouse witness told the truth during one of New Zealand's most captivating and high-profile murder trials.

The identity of Witness C is suppressed, but his testimony in the 1990 trial of David Tamihere helped lead to a guilty verdict for killing Swedish tourists Urban Hoglin and Heidi Paakkonen.

However, Witness C is now accused of, and denies, perjury and attempting to pervert the course of justice for what he said on the stand. He has been on trial in the Auckland High Court this week.

The jailhouse informant said Tamihere told him, in detail, while the pair were in prison together that he killed the Swedes. Tamihere has always professed his innocence.

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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.

In his closing submissions today, prosecutor Murray 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 murder trial.

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

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.

Paakkonen's remains have never been found.

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.

"His evidence was safe and difficult to challenge, if only Mr Hoglin had not been found," Gibson said.

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Swedish tourists Urban Hoglin and Heidi Paakkonen went missing in 1989. Photo / File
Swedish tourists Urban Hoglin and Heidi Paakkonen went missing in 1989. Photo / File

Conjecture about Witness C's testimony arose in 1995 when he swore an affidavit stating that he lied and gave false evidence. An interview with the late Sir Paul Holmes in 1996 confirmed the affidavit.

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 has since said he and his family were under threats from other prisoners to sign the affidavit, talk to Holmes, and write the letter because of his reputation as a prison "nark".

"In prison circles narks are considered lower than paedophiles," Witness C's lawyer Adam Simperingham said, recalling a statement from Tamihere, during his closing submissions.

He said Witness C signed the affidavit and recanted his evidence as a matter of survival in prison.

"He did it so he could say, 'leave me alone I'm worth more to everyone alive now than I will be dead'."

Simperingham said it was obvious his client disliked Tamihere, and urged the jury to see Tamihere for what he was.

"We know that he's a convicted murderer, he's gone through the appeals process and those convictions were upheld.

"He's a man who played games during a homicide investigation, he's a game player," he said referring to the varying stories Tamihere told police and other inmates.

Simperingham said Witness C had little to nothing to gain from giving evidence in 1990.

"He befriended Mr Tamihere but became disgusted by what Mr Tamihere told him.

"What did Witness C have to gain by giving evidence? Nothing - certainly no a lot."

Simperingham said Witness C wasn't offered a cash bribe to take the stand, and was never paid a reward.

"No one's come out of the police woodwork 27 years later to say, 'oh yeah, the police did bribe witnesses to give evidence'," Simperingham said.

The perjury case was laid as a private prosecution by Arthur Taylor, serial litigator and Witness C's long-time fellow prison inmate.

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

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.