A letter apparently from double-murderer Witness C and threatening those involved in prosecuting him has been referred to the police and courts.

The handwritten letter speaks of meeting up in the near future with four men involved in prosecuting Roberto Conchie Harris for committing perjury in the controversial David Tamihere murder case.

"I have the instincts of a hunter and love the chase, but its the kill that gave me a deep visceral satisfaction," the letter says.

Signed "Roberto Harris", it also speaks of bringing ice cream to the party, a reference the recipients believe is to a double murder for which Harris is serving a life sentence.

Harris had reportedly referred to the 1983 murders in which he shot a couple in the head at close range as "just like having an ice cream".

Harris was unmasked as Witness C following his conviction for perjury last year for lying at Tamihere's 1990 trial for the murders of Swedish tourists Sven Urban Hoglin, 23, and Heidi Paakkonen, 21.

Harris claimed Tamihere confessed the murders to him.

Harris was found guilty on eight perjury charges following a private prosecution brought by "jailhouse lawyer" Arthur Taylor and argued by lawyers Murray Gibson and Richard Francois.

The Weekend Herald has a copy of the letter which was posted to Mike Kalaugher, a retired chartered accountant who did research for the perjury prosecution and appeared as a witness.

"I was amazed," Kalaugher told the Herald. "We thought we should refer it to the Court of Appeal and Arthur has told the Waikato police about it."

Kalaugher said the reference to ice cream was particularly threatening.

The letter is written in a neat hand but comprises a single paragraph flowing over five pages.

It says in part: "I recall AT [Arthur Taylor] mentioning ice cream so I'll bring the icecream to the party, yous can count on that as sure as night follows day."

And, "Sometimes the only thing more dangerous than a man with nothing to lose is a man with everything to lose. A sport I have missed dearly is hunting ... I have the instincts of a hunter and love the chase, but its the kill that gave me a deep visceral satisfaction."

Kalaugher said Harris had his address for correspondence before the perjury trial. He was familiar with Harris' handwriting and had no doubt the letter was from him.

"I'm not sure when he is planning to have this meeting. Is he going to break out of jail and grab a gun?"

A spokesman said police were aware of Taylor's intention to make a complaint. Any complaint would be accessed.

Harris' lawyer Adam Simperingham said he could not comment as he had yet to speak to his client about it.

On Wednesday, Taylor's lawyer, Francois, sent a copy of the letter to the Court of Appeal which was considering an appeal by Harris who claimed his perjury sentence of eight years and seven months was "manifestly excessive".

The Appeal Court responded that the letter was not relevant to issues in the appeal and that "the appropriate course is for the letter to be referred to the police".

In a decision released Friday, the court dismissed Harris' appeal.

The panel of three judges found that the sentence was well within the available range and that the sentencing judge "would have been justified in adopting a higher starting point".

Harris has convictions for murder, sex offences against girls, fraud, escaping, breach of parole, burglary, possession of a pistol, theft and now perjury.

He has spent 30 of the past 33 years in prison, having twice been recalled for breaching parole.

The Parole Board last year said Harris was "a high and undue risk offender" and "far from being a candidate for parole".

Tamihere, who has always professed his innocence, was convicted and sentenced to life imprisonment in 1990, before eventually being granted parole in 2010.

Tamihere's lawyer, Murray Gibson, has asked the Government for a pardon and is also seeking to have the conviction revisited by the courts via the Royal Prerogative of Mercy process.

Gibson said he didn't feel threatened by Harris' letter.