Counties Manukau police want to hear from people who were near Mercer early last Saturday morning when a woman was killed on State Highway One.
They said Sarah Bromley appeared to have been struck by more than one vehicle.
Detective Sergeant Sam Rice said the police wanted to talk to anyone who may have seen a person walking along the highway or who may have given a lift to anyone.
He said they were particularly interested in speaking to the driver of a white vehicle who dropped a person off near Podges Place pub just before the incident.