Police officers involved in a stand-off with a gunman who had already shot three civilians - killing two of them - acted appropriately by firing at him, a review found.

The Independent Police Conduct Authority (IPCA) has released a report into the incident involving Northland man Quinn Patterson, who fatally shot two women and injured a man when they approached a property he was living at in July last year.

Mother and daughter Wendy Campbell-Rodgers and Natanya Campbell were killed.

Patterson's body would be found in the later burnt-out house afterwards. A post-mortem found he had most likely shot himself before the fire - which he started after a shoot-out with police - reached him.

Authority chairman, Judge Colin Doherty, said: "Police responded swiftly and professionally to an extremely serious and tragic incident.

Natanya Campbell and her mother Wendy Campbell Rodgers were killed by Quinn Patterson. Photo / Supplied

"I am satisfied that the two officers who fired at Mr Patterson had no other reasonable options to protect themselves and their colleagues.

"Mr Patterson was shooting at them from an elevated position and with a powerful semi-automatic firearm. Mr Patterson's own actions precluded a peaceful resolution to this incident.''

Police have acknowledged the IPCA's findings.

Detective superintendent Dave Lynch praised the efforts of those officers called to the property that day after authorities were alerted of the shooting.

Wendy Campbell , property manager from Northland Real Estate, was killed. Photo / Supplied

"I would like to take this opportunity to acknowledge the bravery of the staff who were involved in this incident - particularly members of the [Armed Offenders Squad] who, despite knowing there was an active shooting, still did everything they could to try and save Wendy and Natanya; forming a human shield around them to allow AOS medics to examine them.''

Lynch said police encountered dangerous situations every day. But this particular incident had been fast-moving and highly complex.

"The officers maintained excellent control and command throughout this incident and their professionalism in such tragic circumstances is to be commended," he said.

The IPCA also pointed out that it had considered what information police knew about Patterson and his access to firearms before the incident.

The IPCA concluded that the information available was "disparate and insufficient'' to raise significant concerns or warrant an emergency response before the fatal incident occurred.

It was noted, however, that police should have recorded information about Patterson's failed attempt to import restricted gun parts and empty magazines in the police database.

In response, police said they had no information, at the time, which indicated Patterson posed an imminent or significant threat.