Police have revealed more details about the death of entomologist Stephen Thorpe on Saturday morning.
Thorpe had been at the Blockhouse Bay tennis club, doing work on his laptop at the time, police said.
He then went outside, where a violent struggle took place, ending in Thorpe receiving stabbed wounds before dying at the scene.
Detective Inspector Glenn Baldwin said Thorpe went outside and a short time later "cries for help were heard".
The person who attacked Thorpe likely had blood on them when they fled, but have not been found yet.
Police urged anyone with CCTV or dashcam footage to get in contact.
A staff member working at the club witnessed the victim in a violent struggle and went to get a phone to call for help, Baldwin said.
"This offender will have gone somewhere, likely in an agitated state and likely with some blood on him," he said.
Police want anyone in the area - around Rathlin, Whitney, Exminster and Terry Sts - who saw anything suspicious to get in touch.
"I know this event has rocked the local community and membership at the tennis club," Baldwin said.
There will be an increase in patrols in the area and police urged anyone with CCTV or dashcam footage to get in contact.
Jacqui Knight, from the Moths and Butterflies of NZ Trust, said she had known Thorpe for about 10 years as the trust had a butterfly habitat very close to the tennis club.
Knight described him as being "very tolerant and knowledgeable" of anything to do with insects, which were his passion. He would go on daily walks through the reserve by the club, searching for insects and plants, she said.
"He spent seven days a week at the office - he just loved it. He was a loner who kept to himself most of the time and wouldn't hurt a fly. It's just so tragic this has happened."
Thorpe had no close relatives living in New Zealand as far as Knight knew, and had originally been from Australia.
"He was so well-spoken and just loved the nature here, he was very successful at what he did too and had quite a few insects named after him, I believe."
