"They'd tied the dog to the rear of the car, which we advise people not to do."
He said the dog, which died as a result, had been a "much-loved pet" and the family was "distraught".
"There could be a negligent prosecution, but at this stage it is unlikely we would go down that path".
A police spokeswoman also said police have spoken to the owner of the dog.
She said the owner had visited the Kaikohe Police Station yesterday after reading a news report about the incident.
"He was very upset about the incident and says it was an accident," she said.
Police are continuing with inquiries into the incident.
Roos reported the incident to police and the SPCA, and told the Herald the dog "was on its stomach with its back legs dragging and head in the air".
The Auckland-based South African estimated the vehicle had been travelling about 60km/h on the highway before turning into the unsealed Ambler Rd on Saturday afternoon.
"It looked like a light brown pit bull. I stopped as fast as I could and turned to confront him, but I believe he saw me stopping and he drove away fast," Roos said.
After giving chase, he said he believed the driver turned into one of the first driveways along Ambler Rd, but he did not confront the driver.
When back on the highway, Roos said he looked at the surface and saw what he thought was blood on the road.
"I am not sure how far the dog was being dragged before I saw it.
"I have played the image through in my head quite a few times and I can say for sure that it did look [dead] at that time."