Police have said tasers had to be used on the 29-year-old who died in custody three days after his arrest, for the safety of the police officers involved.
Police have named the man as Alo Ngata, a 29-year-old from Tonga.
The investigation into his death and the circumstances surrounding the assault of the 76-year-old man are continuing after two police officers were forced to discharge their tasers during the incident.
Superintendent Karyn Malthus, Auckland City District Commander, said about 1pm on Sunday police were responding to reports of a man attacking an elderly man on Beresford St, Freemans Bay.
From the Eagle helicopter it was observed the 29-year-old kicked the elderly man in the head five or six times, essentially until he was unconscious, she said.
He then advanced on police in a threatening manner, she said.
The first two uses of the taser were ineffective, the second two were effective, she said.
"He continued to resist police attempts to restrain him, to cuff him.
"It took four police officers to restrain him."
If they had not used the tasers the two police officers could have been seriously injured if not killed, she said.
"I have no doubt that if our officers had not intervened with the necessary tactical options they would have incurred serious injury themselves."
"It would be fair to say that they are traumatised."
During it all the 76-year-old victim was unconscious on the roadway. He received medical attention and was taken to hospital, she said.
Police say the 29-year-old was transported to the Auckland Police Custody Unit in an agitated state and that he continued to resist police efforts.
Malthus said police members realised he was in medical distress, commenced CPR immediately and called an ambulance
"Sadly and tragically, three days later he died."
This was a "significantly violent and volatile" incident, Malthus said.
"Not only for the 76-year-old victim but for police.
"None of our police officers want to come to work and have to deal with this and have their shift end with the loss of a life.
"Any loss of life is tragic."
Police were called to the man's address the day before the incident and are reviewing that as well as part of the investigation, Malthus said.
Police had spoken with the deceased's family "to better understand what happened".
"Any death is a tragedy and we are working with, and supporting Mr Ngata's family, including his parents and wider family who are grieving their loss," she said.
The elderly victim is still recovering in hospital and is reported to be doing well.
An eyewitness previously told the Herald the man was acting like a "wild animal" before he was tasered multiple times by police on Sunday.
The man had attacked an elderly person in Freemans Bay outside a residential address.
"He was out of control," the witness told the Herald.
"He was resisting arrest and he came at the cops as well, he was told to bloody get on the ground and he didn't, so they tasered him."