A Corrections investigation into "fight clubs" at Mt Eden prison found evidence that similar fighting rings were being run at other prisons.
The investigation by Corrections "special monitors" in 2014 also details allegations that staff at the Serco-run Mt Eden prison facilitated fighting between inmates and also assaulted prisoners.
The investigation was unable to substantiate the claims of assaults by staff or that they were involved in facilitating violence, but recommended further reviews take place.
It did conclude there was a fight club operated at Mt Eden Corrections Facility (MECF) - and also found evidence to support prisoners' claims that fight clubs were being "similarly operated" at Northern Region Corrections Facility and Rimutaka Prison, both run by Corrections.
It is not clear what action was taken after the 2014 draft report, but last month Corrections said it had no evidence of fight clubs at prisons other than Mt Eden.
A Corrections spokeswoman said follow up investigations found no evidence of fight clubs at prisons other than Mt Eden.
"Phase 2 of the Chief Inspector's report (released in October) looked in to the existence of fight clubs at a number of other prisons across New Zealand,including Northland Region Corrections Facility and Rimutaka Prison, and found there was no evidence of any 'fight club' activity."
'Prisoners in tears'
Prisoners interviewed as part of the 2014 investigation "displayed real fear and anxiety", the report states, with some becoming tearful while talking about fight club.
Some prisoners alleged staff were facilitating prisoner on prisoner assaults separate to fight clubs.
One allegation was that staff led prisoners to a corridor for the purposes of an interview or appointment. The staff member would then leave, and other prisoners turn up who would carry out an assault on the prisoner.
Another prisoner claimed he was asleep in his locked cell. He then heard the door unlock before gang members entered and assaulted him.
It was also alleged that it was common for prisoners to be assaulted or "king hit" while making their first phone call at the prison. Prisoners reported that staff would turn a blind eye or simply say, "welcome to MECF".
Monitors were also told of alleged incidents when a staff member would walk behind a new prisoner and say, "CSO", so prisoners were aware they were a child sex offender.
The 2014 report could not substantiate such claims, but recommended a further review take place to understand why they were being made.
Fight club controversy
Video footage of "fight clubs" within the Serco-run prison were posted online in July 2015, sparking an investigation by Corrections' chief inspector and eventually leading to the decision to end Serco's contract.
The results of Chief Inspector Andy Fitzharris' investigation were released last month, detailing widespread failings by the private prison provider including violence, drug use, haphazard staffing, and unhygienic conditions within the jail.
The chief inspector's report also shed new light on the earlier 2014 investigation, that took place after a probation officer alleged "a significant amount of fighting".
The draft report's findings were not provided to Serco until May 2015, 10 months later. In addition, Corrections chief executive Ray Smith and then-Corrections Minister Sam Lotu-Iiga were not told about the report.
Corrections said that was because the national commissioner had been concerned about the evidential basis of the report. As a result, it was not finished or escalated and Serco were not notified.
That decision was criticised by Corrections Minister Judith Collins after Fitzharris' report was released this year, and acknowledged by the department as a mistake.
Smith has now released the 2014 report in full, along with two other reports.
One of those was a 2009 report investigating prisoner fighting in the old Mt Eden Prison, which was under the control of Corrections and decommissioned in 2011.
Informants alleged staff were involved in organising fight clubs and were placing bets on the outcome. Prisoners involved in organising the fights were believed to be members of the Killer Beez Gang, the dominant gang in the prison.
The report found it was more likely than not that prisoners were involved in fights in old Mt Eden Prison, but found insufficient evidence to corroborate allegations of staff wrongdoing.
Collins has highlighted that finding as evidence the fight clubs were being run when the prison was state-run.