Police Minister Michael Woodhouse says he is extremely disappointed police failed to do their job properly in investigating a teenage sex ring in west Auckland.
The Independent Police Conduct Authority (IPCA) - chaired by Sir David Carruthers - has found officers failed to adhere to the basic tenets of any form of criminal investigation.
The group of young men, who called themselves the Roastbusters, boasted online about having sex with drunk girls, some as young as 13.
Mr Woodhouse said the report was alarming.
He said if the police had done their job properly they could have prevented further incidents and delivered a different outcome for victims.
"I need to be sure whether this is a systemic issue and a failure of the system or whether it is a disappointing exception to a general trend of increasing support for victims of these crimes, and one which needs to be remedied and is already."
Mr Woodhouse said he had been given an assurance from police that steps had been taken to ensure such failures did not happen again.
Speaking in Parliament, Labour MP Jacinda Ardern said police could not even connect the dots in the case.
She argued that there could have been a different outcome for the girls who complained to police, if the child protection teams "properly pursued the lines of inquiry, accurately recorded and cross-checked information about the offenders [and] properly evaluated all available options to prosecute".
Mr Woodhouse said he agreed with the IPCA's main criticism that police investigating individual cases failed to see a pattern that may have prevented subsequent incidents.
"But it's very difficult to say now whether there would have been a different outcome in a prosecutorial sense," he said.
A separate 12-month police inquiry after the story broke in the media concluded with no charges being laid.
Labour MP Sue Moroney asked whether the Police Minister would "now expect the police to reconsider laying charges in these teenage sexual assault cases". If not, she asked, "what measure will he offer the victims who the police now admit they failed?"
Mr Woodhouse said that was a matter for police, but noted: "In Police Commissioner Bush's comments today ... There is no time limit in the laying of a complaint of sexual assault ... and police would still welcome any complaint being laid by any existing or other victims, and they would take those complaints extremely seriously."
Mr Woodhouse said he was confident police would learn from their mistakes and he hoped it did not put off any victims from speaking up.