Cottrell never regained consciousness and his sister and her husband made the agonising decision to turn off his life support yesterday.
British-born Cottrell had lived in New Zealand for about five years and liked working overnight shifts, saving his leave to travel the world.
He took the same route home each day.
It was not believed the attack on the openly gay and slightly built man was premeditated, or that his sexuality was the reason for it.
"We don't know about Mr Cottrell's sexuality. That may come up in our inquiry but at the moment that is certainly not a focus for us,'' Mr Miller said.
"I cannot see any reason for Mr Cottrell to be involved in an altercation.
"He seemed to be a very quiet person ... I would say it's completely unprovoked (and) he's met one or more persons.''
A 30-strong team was working on the inquiry and wanted to hear from anyone in the area at the time, even if they had not seen the assault.
Hours of CCTV footage from the area was being trawled through and although there was none of the actual attack scene, footage from around it could reveal vital clues.
The taxi driver who found him had not seen anyone else.
A crucial piece of evidence police wanted to recover was Cottrell's brown leather wallet, which was believed to have contained $80 and various cards.
"It's very horrible to be killed for anything but that's [killing for $80] just totally senseless,'' Mr Miller said.
"We'd just like to extend our sympathies now to Mr Cottrell's family and his colleagues at RNZ.
"I can assure you that we're working very hard to bring these people or persons to justice and I have a large inquiry team, very experienced, who are working right through this week and beyond, whatever it takes.''
It was possible a weapon was used in the attack it was hard to say for sure as Cottrell suffered a degenerative bone disease.
"But from my experience, and looking at the injuries, that [the disease] would not be a cause of death. They were very severe injuries.
"The nature of the injuries would certainly indicate that he may well have known those people were there and there may have been an actual confrontation.''
It was "not a very common type of assault and not a very common type of homicide'', Mr Miller said.
However, three other other people were assaulted in the city early on Saturday morning. In one incident, a man was knocked unconscious near Mermaids Bar in Courtenay Place about 4am.
"The person that was assaulted was actually wanting people to fight with him,'' acting Wellington area commander Detective Inspector Steve Vaughan said.
The man had been treated at Wellington Hospital and discharged, and police were searching for two people over the incident.
Two other men, friends Wayan Rosie and Mark Johnston, told The Dominion Post they were attacked by a group of men who piled out of a van and attacked them in Courtenay Place early on Saturday.
Mr Vaughan said the latter incidents were not reported to police but that they were following up reports men in a white van were cruising the central city beating people up.
"I'm certainly concerned about any violence, whether in the city or in our homes or in the streets in our residential areas,'' he said.
"It is very, very difficult to police these isolated incidents where you have people, trouble makers, miscreants, coming into town, taking alcohol possibly and committing offences.''
People should not be afraid to go out but they should be aware of their surroundings and stick with their friends, Mr Vaughan said.
"Wellington is a safe city and we're committed to its safety and we're going to make sure it remains a very, very safe city for everybody to live, work and play in,'' he said.
"I think the majority of Wellingtonians feel safe in their city.''
Cottrell's death was the first homicide in a public place in Wellington this year, and there was only one last year.
Wellington Mayor Celia Wade-Brown said Wellington was a safe city, and that police statistics showed serious assaults had nearly halved since last year.
"One death a year is still one death too many,'' she said.
"While hugely regrettable for the colleagues and family of the victim, we have to put it into some perspective.''
