One of two brothers violently attacked after walking home from a Christmas party remains in a serious condition in hospital.
The 47-year-old man was in Wellington Hospital's intensive care unit this afternoon after being assaulted on Sunday morning in Porirua.
Police said the attack was thought to be a random, "one-off" incident, and the attackers probably did not know the brothers.
The older man was put on life support after he and his 34-year-old brother were bashed in Mungavin Ave, near the Mungavin shops.
Police were today piecing together CCTV footage covering Porirua City Centre to the spot where the assault happened, east of the city.
Acting Detective Senior Sergeant Peter Middlemiss said police were trying to identify which members of the group may have assaulted the men, and which were only bystanders.
Some members of the public had already helped police, but Mr Middlemiss said more information was needed.
"There's probably still people who have seen the assault in its entirety, or some part of it."
One of the brothers was wearing a blue, striped business shirt and trousers, Mr Middlemiss said. The other was wearing a white American football top.
The men were walking home after a work Christmas party. The attack happened at about 3am.
"Because of the time of the year, there were a quite a lot of people walking, returning home after the bars had closed."
Mr Middlemiss said it still wasn't clear what might have provoked the attack, which seemed to be a one-off incident.
"There haven't been a spate of these things happening in Porirua."
Mr Middlemiss said although the group probably presented no ongoing risks to the public, people walking around at night should heed basic safety advice.
"Walk as a group, and look after one another."
Police said a group approached the brothers and "set upon" them.
A member of the public called 111, and as police arrived, the group involved in the incident dispersed.
Mr Middlemiss said anybody with information about the attack or the perpetrators should phone police on 04 2381400.
Police have established Operation Martin to investigate the incident.
Forensic scientists and 20 recruits from the nearby Police College were helping with the investigation.