Police in Wellington say the injuries that led to the death of Radio New Zealand journalist Phillip Cottrell suggest his assailant may have used a weapon.
Police have begun a homicide inquiry into his death.
Mr Cottrell was attacked in Boulcott Street in the central city about 5.30am on Saturday, as he was walking home just minutes after finishing an overnight shift at Radio NZ's headquarters on The Terrace.
Detective Senior Sergeant Scott Millar says Mr Cottrell, 43, was discovered by a taxi driver about 5.40am, leaving a window of only six to seven minutes for the attack to have occurred.
Mr Millar says no weapon has been found and it is unclear how many people were involved in the attack, which he described as vicious.
He says there is no reason to believe Mr Cottrell precipitated the attack, in which his brown leather wallet containing about $80 was taken.
Police are appealing for anyone in the area at the time of the attack to come forward.
Mr Cottrell died on Sunday afternoon after his life support was disconnected, and a post-mortem examination was being conducted on his body on Monday.
Mr Millar says the attack was not caught on security camera but police are reviewing footage from nearby cameras to build up a picture of what happened.
He told Morning Report police are focusing their efforts on finding Mr Cottrell's wallet.
Mr Cottrell had worked for Radio New Zealand as a bulletin editor for five and a half years.
Head of news Don Rood says his death has cast a pall over the newsroom.
"Never in my worst nightmares did I ever imagine that I'd have to handle the death of a colleague and staff member who didn't die doing their job, but was killed in a brutal and unprovoked attack in the street only minutes after leaving the office," he says.
Radio New Zealand chief executive Peter Cavanagh has described the attack as senseless and unprovoked.
He told Morning Report staff are devastated by the death and will be offered counselling services.
Broadcasting Minister Jonathan Coleman has offered his condolences to Mr Cottrell's family, friends and colleagues.
Mr Coleman says he is shocked by the sudden death of Mr Cottrell and he was clearly well-liked and held in high professional regard.
One of Mr Cottrell's closest friends, Lloyd Scott, who is one of the presenters of The All Night Programme, has described him as a skilled writer and a highly professional journalist who had a passion for travel.
When he heard his friend had been assaulted, Mr Scott rushed to Wellington Hospital, but was told Mr Cottrell had suffered extensive brain damage and would not survive.
"From then on it was just trying to get through whatever time it took before they decided and did what they finally did and it became a real black one and a half days," says Mr Scott.
Mayor says city still seen as safer
Wellington mayor Celia Wade-Brown says people feel safer in Wellington compared to other cities.
There were four separate assaults in the city during the weekend, including the attack that led to Mr Cottrell's death.
Ms Wade-Brown says she has confidence in police prevention and apprehension.
She says council staff working in the city around the time of the assaults who may have information will be urged to come forward.