Christchurch Men's Prison director John Roper is among several staff disciplined after an incident last year.

The boss of one of New Zealand's largest prisons has received a final warning after an inmate self-harmed while left on his own without food in an exercise yard for nine hours.

The incident at Christchurch Men's Prison in June last year took nine days to be flagged at a national level after local staff failed to correctly report it.

The Department of Corrections launched an investigation into the security breach, but only after it received a letter from a whistleblower that shed light on the seriousness of what had happened.

DAVID WALKER/STUFF The incident at Christchurch Men's Prison took nine days to be flagged at a national level.

The inquiry identified a series of failings and recommended an array of changes to the way prisoners were checked and managed.

READ MORE:

* Criminal overlooked for hours at Christchurch Men's Prison and left outside

* Christchurch Men's Prison staff will 'face the consequences' for media leaks

* NZ's attitudes to whistleblowers

Several prison staff were punished, including long-standing director John Roper, who received a final warning, and unit manager Doug Smith, who received a warning.

A new deputy prison director position has recently been created to bolster the under-fire management team.

Stuff was alerted to the incident last year by a source, who was concerned prison staff had "tried to sweep it under the carpet".

This week, a summary of the investigation's findings was released under the Official Information Act after a delay, which resulted in a complaint to the Ombudsman and an apology from Corrections to Stuff.

Corrections southern regional commissioner Ben Clark said he did not believe there had been a "cover-up" at the prison, but acknowledged the handling of the incident was "simply not good enough".

"There are a number of things that … should have been done better," he said.

The document obtained by Stuff outlines errors by Corrections staff that meant an inmate waiting to be inducted into the prison's Matai Unit was left in a secure exercise yard without food from 9.45am to 7pm on June 21.

The errors included:

▪ A random muster was held at 2pm, but guards did not clear the yard where the inmate was being held. His absence went unnoticed and the muster sheet was not signed correctly.

▪ The yard was not cleared when all inmates were locked in their cells and given their dinner about 4.15pm. A "face-to-name" check was carried out, but a senior guard expected only one prisoner to be in the cell where the inmate in question was assigned and his absence again went unnoticed.

Corrections staff and a nurse discovered the inmate in the yard when he called out to them as they were moving between units about 7pm.

He had an unauthorised disposable razor and superficial wounds on his ankle and knee as a result of self-harm. He was taken to the health unit for treatment, but no assessment of his risk of further self-harm was made.

The incident was reported quickly to the unit manager, who carried out an investigation the next day.

However, none of the staff involved in the prisoner's discovery wrote reports about what had happened, and it was nine days before the incident was flagged nationally.

Clark said prison management should have alerted him to the incident earlier. By not doing so, they had left themselves open to being accused of a cover-up.

"It's disappointing to see the standard policies and procedures were not followed in this instance and this is simply not good enough.

"We are all human, mistakes will happen. However, I expect that when a serious issue arises, it should be escalated quickly and dealt with appropriately … to make sure it doesn't happen again."

An employment investigation was carried out and "appropriate action was taken", Clark said. Privacy constraints prevented him from revealing further details about the staff involved or the punishment they received.

"The staff have expressed to me that they are disappointed in themselves. They set themselves high standards and know that on this occasion they let themselves down."

Smith, the Matai Unit manager, was the deputy leader of the infamous "goon squad", an elite group of prison guards that operated out of Canterbury and was disbanded in June 2000 amid complaints of bullying inmates and aggressive treatment of members.

One squad member, Alistair Thompson, put his penis on the bar during social drinks at the Kirwee Tavern and allowed Smith to hit it with a beer bottle. Thompson later denied the act reflected the squad's macho culture, but did not explain further.

The investigation into last year's incident made 13 recommendations, including a review of the process for the induction of prisoners into new units. They have all been completed.

Clark said the inmate in question received an apology.

Roper did not respond to requests for comment.