Mills' incomplete skeleton was found at a property in the Auckland suburb of Mt Wellington in Auckland in September 2011 as demolition work was scheduled to begin.
Cooper, his former flatmate, was later charged with murder.
Cooper never disputed his involvement in the death and pleaded guilty to covering it up, but denied murder and claimed he killed Mills accidentally in self-defence.
In August 2013, Cooper was found not guilty of murder - but guilty of his manslaughter. He was sentenced to seven years and three months in prison.
The Herald can reveal he has been released on parole, after being denied in 2017 and 2016.
Cooper, now 30, appeared before the Parole Board on June 18 and will be released in July.
Board convenor Martha Coleman said at earlier appearances before the board Cooper was "frustrated with the failure of the prison to make offence-focused treatment available to him".
At this month's hearing a psychological report was presented to the board stating Cooper had undertaken significant counselling which would continue in the community after his release.
The report said Cooper "has good insights into his offending" and had a "realistic" relapse prevention plan.
Coleman said the issue for the board was whether Cooper needed to complete counselling in prison or "whether that could be continued once he was in the community".
"The Board had some concerns about the adequacy of his safety planning but decided that this was better to be completed with input from his probation officer when in the community," Coleman said in the parole decision.
The board agreed to grant parole, subject to standard and special conditions of release for six months past Cooper's statutory release date.
"One of those conditions is that he will be subject to tightly controlled residential restrictions for at least the first three months of his release," said Coleman.
"Those restrictions will remain in place until he comes back to the board for a face to face hearing… by the end of September 2018 at the latest.
"The board expects by then that he will have completed his safety planning with the probation officer and he will need to discuss that with the board at that hearing.
"The board can consider then whether residential restrictions or any other form of monitored curfew would need to remain in place."
Coleman said other conditions had been put in place to enable Cooper to continue the psychological treatment he started in prison.
Inside he had three out of 10 required sessions.
"He will also be required to undertake an alcohol and drug assessment," said Coleman.
"Grief counselling may also be appropriate for Mr Cooper.
"Mr Cooper was advised at today's hearing that he will not be able to possess or consume alcohol or drugs, and that his compliance with that condition can be monitored once in the community."
Cooper's special conditions include:
• to attend an alcohol and drug assessment, and attend, participate in and complete any treatment or counselling directed by a probation officer;
• to attend a psychological assessment and attend, participate in, and complete any recommended treatment as directed by a probation officer;
• to attend, participate in, and complete any other treatment or counselling as directed by a probation officer
• not to possess, use, or consume alcohol, controlled drugs or psychoactive substances except controlled drugs prescribed for him by a health professional.
Cooper must also live at an approved address and cannot move from there without direct permission from his probation officer.
The board also ordered him not to have contact or association with any victim of his offending - directly or indirectly - without prior written approval of a probation officer.
