A 5-week-old baby was alone in his South Auckland house when he died, and a police child protection team will now investigate whether the "actions or inactions" of those caring for him contributed to his death.
The baby was born in late November and died at about 1pm on New Year's Day at his family home in Battlen Place, Manurewa.
His name had not been released, and it is understood police have been given several different versions of the baby's name including both of his mother and father's surnames.
A post mortem examination was held yesterday to ascertain how the boy died, overseen by a Coroner.
Detective Inspector Jim Gallagher said the post mortem results clarified a lot of things for the investigation team but he would not be drawn on the specifics.
"I am reluctant to say how the baby died. It's relevant for the police ... we still have to complete a lot of work," he said.
"It is not an abuse case. Abuse generally has connotations of physical or sexual harm. This is why it's not in this category. The criteria we're looking at is in regard to issues of the care of this child, duties of care."
The Herald has learned that there was no one else in the house when he died and that police were focusing on whether the child was being neglected before or at the time he died.
Mr Gallagher confirmed the baby was alone in the house, but said people "connected to" the baby were "in the near vicinity". He would not be drawn if they were actually at the property itself.
"From inquiries to date, it is very clear that when the baby died there was no one else in the house," Mr Gallagher said.
"It's within that category [of neglect] that this case is being looked at. "We still have to complete work before we can reach a point where we could start to say whether or not there is a foundation to consider some person should be made accountable for the death of the child.
"It's the police role in every death to determine whether or not there is some accountability for an event like this. There has to be some understanding as to why the baby died, and then to know whether or not any person's actions or inactions contributed to the death."
Mr Gallagher said police were not seeking information from anyone outside the baby's immediate or extended family.
The baby was found dead in his cot by his mother, who then called 111. After police arrived they cordoned off the house so an extensive scene examination could be completed, including calling the Fire Service in to assist with temperature recording devices.
The Fire Service were back at Battlen Place yesterday giving further assistance.