It's the kind of photo any parent would love to show off.

You and your spouse beaming either side of your child, graduation robe draped with fur-trimmed satin colours across their shoulders, trencher snugly atop their head.

Last month, Auckland man Herman Bangera proudly posted such a photo to his Facebook page.

The photo showed himself, his wife Elizabeth and their son Sheal following Sheal's 2014 university graduation, and it quickly sparked a flurry of likes and comments.

"Congratulations", wrote one friend.

"Thanks to the parents for helping. God bless you all."

Bangera responded with multiple love heart and prayer emojis.

As the dozens of congratulatory comments continued, Bangera added love emojis to each, while intermittently posting his thanks "to all".

Five weeks on, Bangera and his wife Elizabeth - known to friends as Elsie - are understood to be the Epsom couple knifed to death in their home on Friday morning in what police say appears to be a "family harm-related incident" with no wider risk to the public.

Detective Inspector Scott Beard, centre, pictured at the scene as police began the double homicide investigation yesterday. Photo / George Heard

A man linked to the double killing, who was taken from the couple's home at the corner of The Drive and Green Lane West to Auckland City Hospital with critical injuries remained in a critical but stable condition last night.

The man is under police guard and deemed to be in police custody, Detective Inspector Scott Beard said.

No formal charges had been laid "at this early stage", with investigations still under way, including autopsies yesterday and today.

The formal identification process is also yet to be completed, but the Herald on Sunday was told last night that the family's immediate next of kin have been notified by police.

A fourth person who received superficial injuries in the incident has been discharged from hospital and was interviewed by detectives on Friday, Beard said.

The Herald on Sunday understands this person may have been a passerby who tried to intervene.

Police remained at the Epsom property yesterday, one of four adjoining flats, and most neighbours said they didn't know the family.

AUT lecturer Ranjana Gupta, whose family own a house next door, told the Herald hours after the killings she was shocked to learn her former neighbours were both dead.

"Who would kill them? I cannot understand that."

Elizabeth Bangera worked at the University of Auckland, Gupta said.

She did not believe the couple had any other children. Elizabeth's brother had lived with the family previously, but had married and moved out years ago, she said.

"She was a very good lady. They are Christian; they used to go to church. They were very God-fearing.

"They were very humble sort of people. They were very helpful as well. They used to look after our property when we're not there."

A university spokeswoman was not able to comment yesterday. A spokeswoman for Fisher & Paykel Healthcare, where Herman Bangera was understood to work, couldn't be contacted.

The couple immigrated to New Zealand from the Indian state of Goa and moved into the block of flats around 2007 because it was in zone for Auckland Grammar where their son attended, Gupta said.

Her friend also said Sheal had since graduated from Massey University engineering school and started his career, Gupta said.

She received a call yesterday from her own son telling her of the deaths.

Two people were killed in the Auckland suburb of Epsom after a stabbing incident. Photo / George Heard

He was at the property just before the alarm was raised to check on work done an hour earlier to trim overhanging trees between the Bangeras' home and the Guptas' property, which is now rented.

There was no sign of any trouble or disturbance, the man told the Herald.

Elizabeth Bangera had an hour earlier spoken to the tree cutter, who also told him a "young guy" had offered to throw the tree branches over [the fence], the man said.

"Half an hour later I got a call from our tenants saying, 'Something's happened next door, that lady that you guys know well, she's been stabbed'."