Detective Senior Sergeant Ross Patterson said they were seeking sightings of a blue and grey Toyota Prado which was travelling south on the expressway at speed between 11.45pm and 12.05am.
"We're piecing together what occurred leading up to the crash, to establish exactly how this horrific tragedy happened.
Engine fluid and police road markings stain the northbound lane of Mangaharakeke Dr/SH1 while an area of bush is left crumpled after the two-car crash today. Photo / Belinda Feek
"To date, the public has been very supportive of our inquiries, but we would still like to hear from anyone who saw a blue and grey Toyota Prado travelling south on the Hamilton Expressway at speed, between 11:45pm and 12:05am, or anyone who witnessed the crash."