He hid his flatmate's body and later smashed Mills' skull before disposing fragments of it at the house next door.
Cooper appeared at a Parole Board hearing last month for further consideration of parole on a seven years and three month sentence for manslaughter and obstructing or defeating the course of justice.
It is understood he is being released to an address in Tauranga.
A decision put out by the Board said: "The facts of this offending are unusual.
"Mr Cooper got into an altercation with a friend who was living in the shed at the back of the property.
"Mr Cooper inflicted a fatal blow during an argument and then took steps to conceal the facts of his death.''
The board noted that Cooper's sole other criminal conviction was for a driving offence - driving while disqualified.
Board members were also told by a psychologist Cooper had been identified as being "low risk'' in the community.
Cooper's release this month is subject to standard and special conditions of release for six months past his statutory release date - September 6, 2019.
"One of those conditions is that he will be subject to tightly controlled residential for at least the first three months of his release,'' the board said.
"Those restrictions will remain in place until he comes back to the board for a face-to-face hearing in September 2018 and 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 the hearing.''
The board is due to consider then whether any residential restrictions or any other form of monitored curfew would remain.