The mother of an intoxicated teen who died after being struck by a police car has condemned the independent police watchdog's ruling over his death.

The actions of 16-year-old Rawiri Riro Wilson contributed to the 2009 tragedy, the Independent Police Conduct Authority has ruled.

Wilson's mother, Sharlene Wilson, told TV3: "It really shocked me for someone like that to take a life and then find they had got away with it.

"We have come away with this and we have got nothing out of it."

The Northland teen died shortly after being hit by a police car late at night while he and his 14-year-old brother and 16-year-old cousin were walking along State Highway 1 to a party near Ohaeawai.

Earlier that night, Wilson had been seen smoking cannabis and consuming alcohol.

It was a dark but clear night, and the officer driving the police car that struck Wilson did not have his vehicle's lights on high beam.

The IPCA said while the officer's actions were not unlawful, it stated "his failure to have his headlights on high beam were unreasonable and undesirable pursuant to the Independent Police Conduct Authority Act 1988".

It added that driving in fog with lights on low beam were not the actions of a "reasonable and prudent driver''.

And two months after coroner Garry Evans ruled the tragedy could have been avoided had the officer been driving with his lights on high beam, the IPCA has taken issue with Wilson's actions.

It's report concluded that the trio of pedestrians were "not mindful of the risk to which they were exposed'' as they walked along SH1.

The IPCA added in a statement: "The investigation has also established that Rawiri Wilson and his cousin were under the influence of alcohol and cannabis at the time, and were not mindful of risk or exercising caution as they walked on an unlit section of SH1 at night.''

The IPCA investigation included speaking to other drivers who had walked past the trio.

They were told the group was acting in an "unpredictable manner''.

One witness said the group was "play-fighting'' or "horsing around'' on the road, including along the centreline of the highway.

One driver said he had "to veer into the middle of the road to make sure that I missed him [one of the trio].''

While critical of Wilson's actions and the failure of the police officer to drive with his lights on full beam in the dark conditions, the IPCA says it was unable to "establish'' if the officer was using his personal cellphone at the time of the collision or in the seconds before it.

But it did say it was "of the view'' that he would have been aware of an incoming text message 20 to 30 seconds before the impact.

"At the time, it was not unlawful to use a mobile phone while driving,'' the IPCA said.

During its investigation, the Authority recommended that police seek an outside legal opinion as to whether the officer could face criminal charges for his driving.

Acting on the advice of the Auckland Crown Solicitor, the New Zealand Police Department decided not to prosecute.

Following the release of the findings of its report into Wilson's death, the IPCA did not make any policy recommendations.