As a vicious attack went on in the Dunedin courthouse cells, Corrections officers had to peer through a scratched perspex pane to make out what was happening.
Three Otago Corrections Facility inmates - Wade Bartlett (33), Jahmyn Inia (25) and Hawi Kingi (22) - had been transported to the court on the morning of June 8 after they attacked another prisoner in the exercise yard two months earlier.
At 8.50am, while awaiting their appearance before a judge, the gang members turned on each other.
Corrections officers had given the men a cup of coffee and had returned to the smoko room when they heard a ''strange sound'', documents released to the Otago Daily Times under the Official Information Act showed.
When staff got inside the cell, they saw Bartlett kicking and stomping on Kingi's head and chest.
''Prisoner Bartlett was given direction to stop and move away by both Corrections officers, it took some time for [him] to comply, having a final kick to Prisoner Kingi's head before stopping,'' an event review said.
Inia was also believed to have been involved in the attack on the Mongrel Mob prospect but he was not seen landing any blows, partly due to the state of the window.
''The poor condition of the cell door glass would have impacted on the ability to reliably witness actions of both perpetrators as you approach the door. It is only when you are positioned at the door can you find a spot on the glass to view the interior properly,'' Corrections' report said.
Officers had identified the problem and requested replacement panes four months before the incident.
Ministry of Justice commercial and property general manager Fraser Gibbs said funding had been approved in June and the replacement glass installed in October.
The delay came because of the limited supply of special ''anti-scratch glass'', he said.
The episode also highlighted the need for CCTV to be installed in the cells and Gibbs confirmed that work was also completed in October.
''It is not clear whether the assault sped up the process of the CCTV being installed in the court cells, however this has now been done and will be a valuable tool for safety and security,'' Corrections' report said.
Kingi was unconscious and taken to hospital by ambulance, accompanied by two officers.
The gang prospect was later jailed for two and a-half years on top of his current term for the original pack attack.
Inia got two years, which he will serve without parole because the prison-yard assault was his second-strike offence.
Police did not charge him over the courthouse cell incident.
Later, in the High Court at Christchurch, a judge declined to sentence Bartlett to preventive detention and instead imposed seven years' imprisonment.
''In speaking with the above staff they do not believe they would have or could have done anything additional to stop the [cell] assault,'' the review said.
''It appears there has been no indication on why the victim was attacked by his associates.''
Since the incident, the court's senior Corrections officer advised bosses he and his police counterpart had developed a ''more thorough approach'' in managing prisoners and offenders in the cells.