"As well as being a favoured fishing spot - including for Mr Beale - the reserve is a popular area for dog walking, cycling, and other recreational activities."
Police had identified, or spoken with about 20 people who had been there that evening, however Foster said they were now looking for three Maori men seen fishing there.
"They're not suspects at this stage," he said.
"But we need to get an accurate idea of who was down there."
The three men had been at the scene playing loud music "into the early hours of the morning".
Police were appealing for the men, or anyone who had seen them, to come forward.
Foster said police were seeking information about any questionable vehicles seen parked at the two carparks near the area - one at the end of Grange Rd, the other off Domain Rd.
At this stage police were unsure when exactly the assault occurred, but believed it was between 8pm on Sunday and 6am Monday.
Alternatively, information can be shared anonymously via Crimestoppers on 0800 555 111.