Hamilton police are focusing their investigation into the slaying of an elderly man, who died in the city last weekend, on finding the people who took the victim's car from a ditch.

Donald Alfred Stewart, 74, of Wellington, was found dead with head injuries near a public toilet on London St in the central city on Sunday morning.

Mr Stewart's Peugeot car was later found at an Auckland wrecker's yard and police said that could provide a vital clue to solving the mystery.

"The wrecking facility is co-operating with police," Waikato police spokesman Andrew McAlley said.

The car was taken to Hamilton on Wednesday where it was pulled apart and parts were cut off by firefighters for forensic examination.

Mr Stewart was captured on security footage filling his car with petrol in Hamilton on Saturday night and the car was seen early the next day in a ditch in the city.

But on Monday when police went to recover the vehicle, it had been removed.

Mr McAlley said finding the people who took it from the ditch was "a focus of our inquiry".

He would not comment on what Mr Stewart's family had told police about why he was in Hamilton.

The family spoke to media yesterday.

His brother Gordon said the family was "shattered and in shock" over the way he died.

"We can't understand what motive anyone would have to do that to him," Gordon Stewart said.

Mr Stewart died from a blow to the head but Mr McAlley said no weapon had been found. He had an injury over one eye.

Mr McAlley said police wanted to hear from anyone who saw Mr Stewart's car, a white 1989 Peugeot 405 GRI sedan, registration number OH8316.

Detective Inspector Lance Burdett said forensic results from the car were still some time away.

Inquiries were still continuing into Mr Stewart's movements and police asked for any sightings or friends of Mr Stewart to come forward with any information that might assist.

"We would like closure for the family," Mr Burdett said.