Greg Newbold, Professor of Sociology at Canterbury University, said the offender would not have known how much - or how little - money Cottrell was carrying and that the attack was motivated by sport.
"They pick on a weak, inoffensive, effeminate-looking guy who doesn't look like he could hurt a fly and they beat him to death for his wallet,'' Prof Newbold told APNZ.
"That for them is sport.''
"They don't really care about the money. It's not enough to worry about. It's wrong to say they did it for the money.''
Such people had invariably been abused themselves and were simply replicating their early experiences.
Society should be hugely concerned that children were growing up exposed to such abuse and violence, and were then going on to perpetrate it themselves.
"You get a dog or a horse and abuse that dog or horse when they're little and they'll always be screwed animals,'' Prof Newbold said.
However, people had to stop blaming others and take responsibility for their own behaviour, he said.
A post-mortem examination on Cottrell started yesterday and was still going late this afternoon, a police spokeswoman said.
It would help to establish whether a weapon was used in the attack and what role that played in Cottrell's death, given that he suffered a degenerative bone disease.
However, police did not believe the disease was the cause of death.
Inquiry head Detective Senior Sergeant Scott Miller said earlier today that whoever attacked Cottrell would have told someone.
"They may have told in the early stages when they thought it was just an assault but someone out there will know something from these people, and they need to get of us immediately,'' he told RNZ.
Police also wanted to urgently hear from several people seen in CCTV footage around the area of the attack, including a man and woman seen walking up Boulcott Street about 5.30am.
A courier van driver seen in the area, and the diver of a third vehicle which was yet to be identified, should also contact them.
"That tells us that at least two people and three vehicles were in the Boulcott Street area at this time.'' Mr Miller said.
"They're definitely witnesses.
"A lot of people who have been in the area may not have seen anything but they might be able to help us with what we term as a big jigsaw of putting all the pieces together.''
Mr Miller said the attack was random and what police called a "whodunnit homicide''.
"The way we would look at it is, with Mr Cottrell out walking, the person or persons he's come into contact with or had a confrontation with, they've got nothing to do with him,'' he said.
"So we don't have a starting point as we do with many inquiries where he may have known or had some association.
"Certainly, the key to it for us is any members of the public with any information, no matter how small, we need to get hold of it.''
A 30-strong team was working on the inquiry and Mr Miller remained confident police would find the offender.
