One of the least satisfactory features of New Zealand's criminal justice system is the use of one prison inmate's testimony against another, usually in the form of incriminating comments the prisoner claims to have heard from the accused who has been in custody awaiting trial.
The failings of the practice have been laid bare this week with the disturbing revelations involving a prisoner who for years has been anonymised as Witness C.
The public now knows — but only after a long and costly battle to identify the prisoner and his criminal record — that Witness C, one of three secret informants called by the Crown in the 1990 murder prosecution of David Tamihere, is double murderer Roberto Conchie Harris.
It is a stain on the system that it took yet another inmate, the "jailhouse lawyer" Arthur Taylor, along with barrister Murray Gibson, to succeed with a rare private prosecution to expose Harris as a liar.
Harris was convicted last year on eight counts of perjury arising from the Tamihere trial.