Surveillance footage has shown two people walking along Boulcott St around the time Radio New Zealand journalist Phillip Cottrell was attacked.
However police said the pair were not believed to be his attackers, and called for them to contact police to help with inquiries.
Cottrell, 43, died in Wellington Hospital Sunday after the attack in Boulcott Street, in the central city, early on Saturday morning.
He had left his overnight shift as a bulletins editor at Radio New Zealand (RNZ) on The Terrace at 5.30am and a taxi driver found him unconscious in Boulcott Street at 5.41am.
Head of the investigation Detective Senior Sergeant Scott Miller told Radio New Zealand a post mortem on Mr Cottrell is expected to be completed later today, while police would extend the scope of CCTV footage they are reviewing.
"We're looking at top of Boulcott, along the Terrace, the Plimmer Steps area, and on the bottom of Boulcott on Willis and Lambton Quay."
Mr Miller said CCTV footage reviewed so far had shown at least two people and three vehicles were in the area around the time of the attack.
"We believe that probably around 5.30 a male and female walking up Boulcott St. We picked that up [on CCTV] on one end of Boulcott St. We don't know if they have seen anything, but it is extremely important if that was you to get hold of police."
Mr Miller said the pair were "definitely witnesses" which could assist inquiries, as opposed to suspects.
"They may have seen something totally unrelated to the attack, but may help us greatly piecing it together.
"Also we have a courier van which we haven't identified the company, which we believe was driving up Boulcott St, we have a taxi and we have a third vehicle, at the moment we can't identify that vehicle."
Mr Miller said neither Mr Cottrell's wallet or any of its contents have yet been located.
He said police still had confidence in finding the journalist's attackers.
"This is what the police call a 'who-done-it' homicide. It's a random attack ... the person or persons that he has come into contact with have nothing to do with him. So we don't have a starting point like we do in many inquiries where he may have known or had some association [with the attacker].
"There is a good chance whoever has done this attack would have told someone.
"There's someone out there who will know something from these people and they need to get hold of us immediately."
- Herald Online Staff