Renowned journalist Derek Round died in a "horrific attack" in the living room of his Wanganui home, a forensic examination has revealed.
Round, 77, a former foreign correspondent, was found dead this week.
It was reported that Round once worked as a spy and had links to the KGB.
A cousin, Martin Round, told 3 News that the murdered man told him he planned to write memoirs that would reveal his work as a spy.
The news clip alleged that when former Prime Minister Keith Holyoake made a comment that could have identified Round as a spy in 1962, two Soviets were expelled from New Zealand.
A police spokesman said this was not a line of inquiry the police were following.
They did not release details of exactly how Round was killed.
They said members of the public could hold the key to piecing together the puzzle.
Sightings of Round's 1996 blue Jaguar XJ6 were key.
"It's a pretty distinctive vehicle," the spokesman said. The car left Round's property in Campbell St after 7pm on Wednesday.
Police also want Wanganui residents to look out for clothes in the area that could be linked to the attacker.