"In a school, in daylight, obviously the worst may have been perpetrated upon her. I thought to cover her up but refrained as I did not want to frighten or startle her any further than the state she may have already been in."
The witness stayed with the woman until police arrived a short time later.
Soon after they arrived a man turned up, recognised the woman, ran to her, assisted her and cried, he said.
"When the police said I could leave, she still hadn't said anything to them but an ambulance had turned up to assist her," he says.
"My heart aches. I felt helpless and am now full of ideas of what I should have done for her. It will take a while for her image to fade in my head."
Mr Allcock said the attack was among the worst he had seen in 28 years of policing.
He said it was too soon to say whether the woman was sexually assaulted, but he described the attack as shocking.
"In my 28 years of policing I'd say it was extremely serious. It's pretty unpleasant. It's a shocker, and in broad daylight,'' he said.
Mr Allcock said the victim had not yet been able to give a description of her attacker to police.
However it was possible the man had approached another woman in the same area before the assault.
"A guy approached her in a menacing manner within the hour before the other woman was attacked. That woman was from overseas and she's gone home and phoned her mother overseas and told her about it.
"The mother has then read the story about the assault (on the 27-year-old) online and contacted police here.''
Mr Allcock said officers spoke to her yesterday and were working to ascertain whether the incidents were linked.
"We don't know yet if they are related but we're very keen to find out so we can get an idea of what's going on in the area.''
He said in both cases the man was "brazen'' and police would be out in force over the next few days door knocking around Mt Roskill in a bid to get more information.
"Members of the public would have seen something. They might think that what they have seen is innocuous, but they should contact police and let us decide. They can expect to see officers in the area making extensive area inquiries.
"We don't want people like this wandering the streets. People like this need to be caught and put away.''
Mr Allcock urged people to report any suspicious behaviour in the area, and to contact police if they they have been approached by a man in the area - whether it be menacing or not.
He also urged people to be careful when walking in the area alone.
"It's better if you can stick to road and paths that are clearly visible, and carry your cellphone with you. And at night, there are a range of other precautions you can and should take.
"In broad daylight you're not going to expect someone to approach you and do that ... be vigilant.''
