A Queen's Counsel investigation into Paparua Prison's former renegade prison officer "goon squad" has slammed the Corrections Department and found the unit developed an "inappropriate militaristic culture".

Inquiry head Ailsa Duffy, QC, today released a report following an extensive investigation into the Correction Department's handling of the Canterbury Emergency Response Unit (CERU).

It found there was no clear line of management, resulting in no clear line of accountability.

"Every investigation the department established to look at allegations of inappropriate behaviour in the CERU was poorly conceived, narrowly constrained and without the capacity to examine the full picture," the report said.

"In this way, the department lost opportunities to learn from the CERU incidents."

The rogue Paparua Prison-based unit was disbanded in June 2000 amid complaints of bullying from inmates and militaristic treatment of its members.

These included donning riot gear, stomping through prisons late at night, shining red laser lights into cells, and rattling cell doors to provoke a reaction from inmates.

Corrections Minister Paul Swain commissioned an inquiry a year ago after political pressure from Opposition members and prison critics.

The report found there was little wrong with the management systems, policies and procedures during the CERU's life.

"The problem was that for most of its life, to some considerable extent, the CERU was able to operate outside those systems, policies and procedures."

During the inquiry, Ms Duffy interviewed more than 70 people about events which are now four to five years old.

The unit originated from a need to resolve staff and union demands for additional support from prison officers at the then newly built Paparua Remand Centre at Christchurch Men's Prison, the report said.

"The unit then appears to have self-evolved from what was intended to be a fairly low-level temporary support unit to being a highly specialised dedicated emergency response and crime prevention unit.

"The absence of clear line management meant there was no clear line of accountability; in these circumstances the unit was able to develop an inappropriate militaristic culture."

State Services Commissioner Mark Prebble said today the matter had led to unhappy relationships between department staff in the Canterbury region that had not been resolved despite two internal investigations and an investigation by the Prison Inspectorate.

"However, it was necessary in order to address the long standing and corrosive effect of the ongoing allegations on Canterbury region staff," he said.

The findings were a reminder that people did make mistakes, but it was management's job to identify errors, investigate circumstances and take any prompt action required.

"Running a prison is a hard job," Mr Prebble said in a statement.

"It is clear that this was a complex set of events that occurred in the middle of a large and complex organisation."

If the department's own internal procedures had been followed during the first investigation in 2000 the matter could have been resolved earlier and avoided the need for the State Service Commission inquiry.

"For New Zealanders to have trust in government, government employees and agencies must model the highest standards of behaviour," he said.