Last night, Detective Inspector Scott Beard said an autopsy had been completed and confirmed that Mr Gillman-Harris died of a severe head injury caused by being struck heavily.
He would not say whether a weapon was believed to have been used.
"We have received a lot of information from members of the public regarding the identity of the two people shown on CCTV, as well as some important background on Mr Gillman-Harris' life," said Mr Beard.
"We'll be looking to put all this information together in the next stage of the investigation."
Police could not comment on Mr Gillman-Harris' background, or any possible motives for the attack.
In a Facebook tribute, Mr Gillman-Harris' nephew Ihaia Harris said it was only a matter of months ago that he saw his uncle.
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The victim
•Ihaia Gillman-Harris
"Please forgive me for not being there to protect you.".
Mr Gillman-Harris worked as a team leader assistant at KiwiRail's Auckland's Southdown freight terminal. In a recent staff newsletter he was among employees recognised for employment anniversaries. He had been with KiwiRail for 10 years.
Spokeswoman Jenni Austin said his death was very sad.
"Our thoughts are with his family and friends," she said.
"We will be supporting his colleagues as necessary and also providing any necessary assistance to police."
Mr Gillman-Harris listed a property in Kaikohe, owned by a relative, as his home address on financing records for a number of cars he had purchased including the Range Rover, a BMW, two Rolls-Royce Silver Shadows and a Ford Mondeo.
His family will take his body to Piki Te Aroha Marae in Okaihau, near Kaikohe, for his tangi.
Additional reporting: NZME.
