David Tamihere secret witness Robert Harris tried to sue Corrections with fake threats

Newshub can now reveal more dishonesty from the double-killer who lied at David Tamihere's murder trial.

Robert Harris used falsified documents to try and sue Corrections for $25,000 and also lied about providing financial support for the children of a couple he murdered.

It was April 2010 when Harris concocted an elaborate scheme from his prison cell to fabricate a case against Corrections.

The story went like this. While at a cafe in Albany, a Corrections staff member lost his prison file containing sensitive information and addresses.

Harris, his grandmother, his sister and one of his victims were subsequently sent threatening letters from anonymous thugs.

The letter to his grandmother and a girl Harris had sexually assaulted contained the following threats: "We know were you's live...you'll be bashed an raped, acid thrown in your faces to leave you as monsters, your f***king house will be burnt to the ground (sic)".

"He's an unapologetic liar really, I'm afraid to say," Tamihere's lawyer Murray Gibson told Newshub.

"It was a typically audacious attempt by Harris to really pull the wool over the tribunal's eyes."

Here's where it fell apart - the Human Rights Review Tribunal discovered a couple of anomalies in the apparently anonymous letters.

Most notably in the phrase "bashed an rape". The "d" dropped out was found in other letters Harris himself had written around the same time. Then there was the unusual use of the apostrophe in "you's".

"The irresistible conclusion was that Harris had written the letters and presented them as coming from an anonymous source," Mr Gibson said.

Mr Gibson wants a review of secret witnesses and says Harris should have never been allowed to testify in Tamihere's case.

"Police and the prosecution must have really been aware of the background of Harris and yet they presented him as a witness of the truth."

Harris also forged a letter to the Parole Board saying a trust fund was "in existence" for the children of Carol Pye and Trevor Crossley - the couple he murdered in 1983.

It purported to be from his lawyer but when asked by the board, his lawyer responded: "I did not write it and I am concerned about its existence."

Not surprisingly Harris had another excuse for that letter, telling the tribunal it had been "done as a joke by a late cousin of mine".

Harris' case against Corrections was thrown out.