The Independent Police Conduct Authority says a police officer who hit speeds of 200kmh during a pursuit which later saw two people die drove dangerously.
The incident took place in October last year, and saw the car fleeing police leave the road at high speed and hit a tree.
Two passengers died in hospital, while the driver and two others were seriously hurt.
"The speeds at which the officer drove on this occasion were clearly unjustified and constituted dangerous driving," Authority Chair, Judge Colin Doherty said.
"Indeed, it is the Authority’s view that rarely, if ever, would driving on a public road at a speed of two and a half times the posted speed limit not constitute dangerous driving."
In a release, police acknowledged the findings.
The incident occurred in the early hours of the morning when officers were conducting speed checks near Great North Road.
A Volkswagen Golf was observed travelling at 133kmh in an area with a 80kmh speed limit.
Police say the Golf was followed and then a pursuit initiated which lasted 1 minute and 16 seconds.
The Golf crashed near the St Luke’s Road off-ramp, resulting in the deaths of two passengers, Connor Talaimanu, 29, and Sharina Storm Meuli, 25.
The driver of the Golf, Prushya Chaichumphon, was last week sentenced to three years imprisonment after facing two charges of reckless driving causing death and two charges of reckless driving causing injury.
IPCA also finds that a criminal investigation should have been initiated into the officer's driving
"This was an absolute tragedy which could have been avoided had the fleeing driver chosen to stop when signalled by police," assistant commissioner Tusha Penny said.
"It is important to note that the IPCA finds the pursuit was justified, and that the officer complied with the Urgent Duty Driving policy.
"The IPCA also makes no finding regarding the pursuit and the cause of the crash.
"However we accept that the officer’s speed was not justified, was excessive, and the pursuit should have been abandoned."
The IPCA also finds that a criminal investigation should have been initiated into the officer's driving.
"I would like to be very clear that police did consider this matter from a criminal perspective.
"A senior investigator was involved and a detailed legal opinion sought regarding the actions of police that night,” says Ms Penny.
She added: "On this occasion police determined that that the evidential test was not met for a charge of either dangerous or reckless driving as the evidence was not sufficient to provide a reasonable prospect of conviction in court.
"Nevertheless we know we could have done better and we acknowledge the IPCA’s comments regarding the categorisation of this incident and the timing of the legal opinion."