The family of Anastasia Margaret Neve are shocked and overwhelmed after learning her Dunedin death is now being treated as a homicide.

It was initially thought the 35-year-old, better known as Stacey, and her partner David Ian Clarke, 49, died in a Wesley St house fire, but police are now saying evidence suggests they died before the fire started.

Neve's younger sister Krysta Neve, of Christchurch, said the family were devastated at the development and were struggling to understand why anyone would want to hurt someone so "full of love".

"I think for anybody who hears someone in their family has been murdered, it's a shock.

"She was a beautiful soul, an independent, very strong woman, and she was a loving 'mother' to her dog Hunnie," said Krysta Neve.

"She was affectionate. She was just everybody's friend, always bubbly, always welcoming people with open arms and going in for the hug.

"She was full of love."

She believed Clarke was also a kind person and good to Neve.

On social media, many gave heartwarming tributes to the couple, but most said they would miss Neve's "smiley face", her "gentle soul with endless love for your friends and family", and her ability to "always turn a bad day into a good one".

A 46-year-old man appeared in the Dunedin District Court yesterday, charged with arson.

He was remanded in custody by consent and granted interim name suppression by justice of the peace Russell Atkinson until his next appearance in three weeks.

Southern Police District investigations manager Detective Inspector Steve Wood said no one had been charged in relation to the deaths yet but further charges were likely.

The bodies of Neve and Clarke were found inside 66B Wesley St, South Dunedin, last Monday.

"Police are now treating the deaths as a double homicide and evidence suggests that they died before the fire started," the detective inspector said.

The man charged with arson was known to the victims, Wood said.

A forensic pathologist has done post-mortem examinations and the bodies have been returned to their families. "However, police are not releasing the cause of death at this time as those details are significant to the investigation, and public release could later compromise evidence."

When asked if drug links were part of a motive for the murders, he said that information would form part of the police evidence.

"This is a complex investigation, complicated by the fire damage.

"We're not ruling out anything." Wood confirmed police were aware of the address and the occupants before the fire, but declined to say why they were known to police.

He said there was still a lot of forensic data to analyse and compare which would take several weeks.

Wesley St residents are horrified the incident is now being treated as a homicide.

Neighbour Mel Ryall said she was "pretty shaken up" by the news.

"To find out this morning that it was a double homicide ... It was right outside my door. For it to happen right in my backyard is just horrifying.

"I only knew them as people that lived there. I didn't know them by name. Everyone knew who they were, but nobody knew anything about them," Ryall said.

"They kept to themselves really."

She said she had had her suspicions it was "not just a house fire".

Another resident, who declined to be named, said it was "really scary".

"You don't think this stuff would happen so close to home.

"It's scary and worrying because, with it being such a small neighbourhood, you'd think somebody would know something - that it was getting that serious.

"But people get murdered, and nobody knows anything. That's really scary."

She said she had bumped into the pair several times while walking down the street with her children.

"He was always on the phone - he always seemed to be stressing out. But the lady was always nice. She was always coming and going - quite friendly. I got the impression they liked to keep to themselves."