A criminal investigation is under way into an undercover police officer's confession that he lied in court and wrongfully sent at least 150 people to prison.
Patrick O'Brien wrote to Chief Justice Dame Sian Elias and former Police Commissioner Howard Broad admitting to perjury, saying he was racked with guilt after carrying a "dreadful secret" for more than 30 years.
He was an undercover agent in drugs operations in the 1970s, immersed in the criminal underworld and the star Crown witness in the resulting court trials.
But Mr O'Brien says he lied on oath every time he testified, and sent a confession letter in November 2007.
The police hired Wellington lawyer Bruce Squire, QC, to investigate.
He interviewed Mr O'Brien in July 2009, and reviewed court files dating back to 1974. Mr Squire finished his inquiry and sent his report to the police, but would not comment on his conclusions.
He said the report was sent to police more than a year ago.
His terms of reference were to confirm the truth of Mr O'Brien's allegations and determine whether police should investigate.
Now, the file has been handed to Detective Inspector Bruce Scott, head of the Waitemata district CIB, to look further into the perjury claims.
Mr Scott emailed Mr O'Brien last week requesting a meeting.
"As a result of Mr Bruce Squire's report, the former Deputy Commissioner directed that I make enquiries into the matters raised by you and consider any criminal liability," Mr Scott wrote.
"I have read the report produced by Mr Squire and also read the interview conducted with you. I have further looked at the evidence that you gave in Court from the transcripts that were available to Mr Squire.
"I am wanting to know if there is any other information that you have that may assist me in determining any criminal liability, or are there other persons that you consider need to be spoken to that could assist an enquiry relating to these matters?"
Mr O'Brien said he would co-operate fully with the inquiry and plead guilty to any charges.
In his confession, he said he could not guess the number of people who were convicted and imprisoned "because of my lies" as he stopped counting arrests at 150, halfway through his three-year undercover stint.
"In every case I lied to the courts and I lied to the juries to obtain convictions against my targets.
"Telling lies was easy - 'policemen don't tell lies' - and my targets never stood a chance."
Mr O'Brien said he was often high on drugs, including cannabis, cocaine, heroin and LSD, during undercover operations. But he denied this when questioned at trials.
He now considers he was a drug addict at that time in his life.
In some cases, Mr O'Brien said he directly lied and said people sold him drugs - when they did not.
Tampering with evidence was also common, he said. Often the exhibit before the court was not the drugs he bought from the target.
The shame and stress of the work broke Mr O'Brien. He resigned from the police and fled New Zealand, "haunted, traumatised and scared".
"My life since has been a tragic waste; running, always running, but never able to lose the demons that rush around in my head."
Mr O'Brien was honoured for his undercover work by former Governor-General Sir David Beattie, who as a judge presided over a series of drug trials in the High Court at Hamilton in 1974.
Sir David wrote a glowing commendation of the young constable to Police Commissioner Ken Burnside, describing him as a credible witness.
But Mr O'Brien confessed to Dame Sian: "In every case and on every charge, I lied to Sir David and I lied to his juries."
What he did
Patrick John O'Brien was an undercover police officer between 1974 and 1977. He says he committed perjury by telling lies while giving evidence at trial, and that he:
* Was often high on drugs while undercover, but denied ever using drugs when giving evidence at trials.
* Asked a suspected burglar to help break into a pharmacy in Hamilton but told a jury the man invited him, and he denied "entrapment".
* Told a jury that an accused drug dealer sold "buddha sticks" to him. The drugs were actually sold to someone else.
* Tampered with evidence by skimming drugs from bags for his own use.