Police did the right thing in two pursuits which killed several teenagers within a week of each other, including one linked to a gang, the Independent Police Conduct Authority (IPCA) says.
The IPCA looked into the first pursuit early on January 24 this year in which a stolen Nissan Lucino failed to stop for police.
Inside were the 15-year-old female driver and her 16-year-old female passenger Eden Nathan who were driving 115km/h in a suburban 50km/h zone in Papatoetoe.
Officers reported the car had run two red lights and items were also being thrown out the window. They told the Police communications centre there was no other traffic on the roads.
The four-minute pursuit ended when the young driver lost control and collided with another vehicle.
Eden was killed, and the driver, who has "extremely serious injuries" is still in residential care almost eight months on.
The driver of the other car was uninjured.
At the time of the crash, Newshub reported the incident flowed from the rules of a gang calling itself 'Pretty But Gangsta' (PBG).
A relative of the 15-year-old said the rules of the gang were that stolen cars had to be taken on joyrides to lure police into chasing them.
The second incident happened early on January 31 in Masterton where officers saw a car speeding where they signalled for the car to stop.
When they got closer, they noticed the car matched the description of a Honda taken from Featherston earlier in the night.
The car sped off through a 'stop' sign at more than 100km/h, but police considered it too dangerous to continue the pursuit because the vehicle was heading toward the town centre where there were a number of pedestrians.
The pursuit only lasted 30 seconds, and as the officers pulled over, they saw the Honda crash - the impact killed Pacer Willacy-Scott and Hoani Korewha, both 15. The 14-year-old driver and another passenger had minor injuries.
The IPCA says in both situations, police were justified in starting the pursuit and had conducted risk assessments throughout.
Chair Sir David Carruthers says the crashes were caused by the teenagers' actions.
"They resulted in the tragic and needless loss of life or serious injury to several young people."
That's a view shared by police, who said the deaths and injuries could have been avoided if the drivers had stopped when asked.
"There is no infringement notice or conviction that is worth the loss of lives we've seen in these two incidents," national road policing manager Superintendent Steve Greally says.
He says the crashes also have a wider impact for the community, family and friends of the victims.