The remains of a woman believed to be Chinese were found inside a bag, fished out of the sea in North Auckland's Gulf Harbour on 12 March.

Police ruled out early on that the victim could possibly be Yanfei Bao, who went missing from Christchurch in July and has yet to be found.

To this day, the identity of the woman in the bag remains a mystery.

Here's what we know so far.

Victim is female, middle-aged

Early on, acting Detective Inspector Tim Williams said police had determined the victim was female and middle-aged.

She was wearing blue pyjama bottoms with pink hearts on it, and a light-coloured singlet with an emblem.

The woman's pyjama bottoms. Photo: Supplied / Police

Stuff reported the singlet was branded with a Chinese logo, translating it to read: "Juan Yan Brand, 80cm, Juan Yan Knitting Garment Factory".

According to Chinese netizens, the brand of the pyjamas is thought to be old-fashioned, perhaps something an older woman would wear. Two shops with that name can be found in the Jiangsu province of China, Stuff reported.

Williams said: "She's small in stature. We estimate the height to be around 160cm. We believe she's of Asian descent and our enquiries lead us to believe she's probably Chinese."

Interpol had been contacted in the hope of identifying the woman, Williams said.

The emblem on the woman's top. Photo: Supplied / Police

Arrests made, four months on from discovery

A man and woman have been charged in connection to the homicide investigation.

The pair, both aged 36, made a first appearance at the North Shore District Court on 1 July.

They were arrested on the evening of 30 June after attempts to leave the country.

The two are each facing a charge of offering an indignity to a dead human body.

They were accompanied by a Mandarin interpreter in court.

The defence counsel's application for continued name suppression was declined, however, their names are still suppressed due to a pending appeal from the defence.

Fisherman pulled body out

Paul Middleton was fishing in the Whangaparāoa area when he saw the bag in the water near Laurie Southwick Parade.

He hooked it and pulled it into the shore, saying it was heavy but easy to move, managing to pull it up the rocks a little.

He thought it might have been a bag of rubbish so struggled through "layer and layer" of plastic to open the bag.

There was "a bit of clothing ... and then there was this hand sticking out".

Paul Middleton speaks with police after finding the woman's body. Photo: RNZ / Nick Monro

It was at that point that he called police.

"Two cops turned up and they thought I'd actually said there's just a hand in a bag and then they went down there and went, 'Oh no we've got a body'," Middleton said.

Middleton said he did not try to open the bag further once he discovered the hand.

Black Notice issued through Interpol

A Black Notice was issued through Interpol in April, and police have received information from a number of countries.

A black notice is an international request for information on unidentified bodies.

It allows police in member countries to share critical crime-related information.

Williams said: "While we cannot go into the specifics, Interpol continues to receive information from a myriad of countries, the most recent being from Canada earlier this month (May)."

Police investigating at the scene. Photo: RNZ / Nick Monro

Police receive more than 140 tips

Last month, Stuff reported police had received more than 140 tips about the mystery woman in the bag.

The tips were based about the circumstances surrounding the woman's death.

At the time, Williams said the investigation team was continuing to work with partner agencies overseas, including "working closely" with Interpol.

"We continue to have a committed and dedicated team who are focused on identifying this woman and the circumstances behind her death," he said.

"Our enquiries are still very much active to determine the who, when, and why."

Williams told Stuff he was still "very interested" in hearing from anyone who might have information about the case.

Plastic wrap helped preserve clues

Otago University lecturer Dr Angela Clark - a forensic anthropologist who also works with police - told RNZ's Checkpoint in March the several layers of plastic the woman was wrapped in could help the investigation by preserving the clothes and slowing the decomposition process.

"It will probably preserve the body for a short period of time, it'll protect the body from the effects of water."

She said the plastic, combined with the immersion in water, would affect the decomposition time.

The plastic would also help to preserve any clothing found on the body, allowing more evidence to be collected.

"The decomposition process will be a lot slower than you might expect if the body was on land."

Dr Clark - who specialises in water forensics - said there were many factors to consider when investigating a body found in the ocean, including the warmth of the water, the speed of the current and how salty the water is.

A hearse arrives at the scene. Photo: RNZ / Nick Monro

She said it could be possible to work out where the body entered the water, with similar mappings on other cases where experts on local water flow were called in.

The body was found floating on top of the water and Clark said this could indicate it had not been in the ocean for long.

But she said in most cases the body would initially sink, before floating back to the surface as the body broke down.

"Water is a very variable medium, so it's hard to predict."

Domestic violence possible

Neil Hallett is a director of Helix Private Investigation Services director who spoke to the New Zealand Herald about the case in April.

He spent 35 years in the New Zealand police before he retired at the rank of Detective Inspector.

Hallett told the Herald the fact she was wearing pyjamas suggested her killing could be a domestic violence case.

Once she was identified, he said he would be looking closely at any partner or ex-partner.

Police still want to hear from people

The investigation team can be called directly on 0800 755 021, or information can be provided via police's 105 phone or online service, referencing file number 240312/9837.

Information can also be provided anonymously via Crime Stoppers on 0800 555 111.