Police want to talk to all drivers who passed over the one-way bridge where George Taiaroa was shot dead last Tuesday.
Taiaroa, 67, was working as a traffic controller for HEB Construction at Tirohanga Bridge, near Atiamuri, in South Waikato, when he signalled for a car to stop while a logging truck crossed the bridge. When the car drove off, he was on the ground with a bullet wound.
A blue Jeep Cherokee, which police said was of interest to the inquiry, sped off from the scene and police say the way the car drove off down the web of rural and forest roads suggested the driver had local knowledge.
Detective Inspector Mark Loper said motorists who passed over the bridge between 2.30pm and the time of the fatal shooting may have information they did not know was important to the inquiry.
"The information those drivers can provide could be crucial in piecing together events leading up the shooting," he said today.
"They may not think they have anything useful to offer but the slightest snippet of information might be invaluable to the investigation, particularly in terms of the people and vehicles they saw as they passed through."
Loper said another focus was finding any security footage that might help the investigation.
"We know that commercial trucks often have cameras mounted on their cabs," he said.
"We also know that farmers and other rural residents often have cameras installed to help protect their properties."
He encouraged anyone in Atiamuri who had such cameras to check them.
Police believed it was not a "random shooting", and that the public was not at risk, Loper told Radio NZ this morning.
"We have a number of people that we have in mind," he said.
"Inevitably what happens is we get a large list of names, and we alibi-inspect those people, and reduce the number until hopefully [we are left] with the main person involved."
At the weekend police started sifting through a number of leads in the murder, including suggestions that Taiaroa was gunned down as a simmering vendetta after his testimony put someone in jail, and that poachers or drug growers were responsible.
Loper told Radio NZ the idea Taiaroa was shot for his testimony was a rumour, but he would not rule it out.