Police have been accused of pressuring the daughter of slain New Zealand woman Karen Ristevski into turning against her father, according to a family insider.

Sarah Ristevski, 22, raised eyebrows last year when she stopped co-operating with detectives trying to solve her mother's murder, apparently in solidarity with her dad Borce, who has been named a suspect in his wife's death.

Mr Ristevski has maintained his innocence throughout the investigation.

Now news.com.au can reveal Ms Ristevski turned her back on detectives because she feared they wanted her to betray her father.

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A family friend who has been in daily contact with the Ristevski family for years and provided key support to Sarah and Borce in the wake of the murder described how police interviewing tactics led to a total breakdown in relations between the two camps.

"They were all co-operative at the start, (and) let the police interview them," the friend said in a series of messages to news.com.au.

"Their houses, cars and phones were and maybe still are bugged, I'm sure. I think they just got sick of it because what first was questioning turned into abuse."

It was the friend's understanding that detectives pushed Ms Ristevski to "turn on her dad because (police believe) he's guilty".

An excerpt of one of the messages sent to news.com.au about police interviewing techniques.
An excerpt of one of the messages sent to news.com.au about police interviewing techniques.
The family friend has denied Borce and Karen Ristevski's marriage was in trouble in the lead-up to her disappearance.
The family friend has denied Borce and Karen Ristevski's marriage was in trouble in the lead-up to her disappearance.

Victoria Police refused to comment when the allegations were put to them by news.com.au.

Karen Ristevski, 47, was last seen at her A$1 million Avondale Heights mansion on the morning of June 29, 2016.

Borce Ristevski told police his wife went for a walk to "clear her head" following a minor argument about money.

Her body was found wedged between two logs in bushland at Mount Macedon Regional Park on February 20 after months of searching.

Police also searched properties at Toolern Vale and Gisborne, about 30km from the Macedon site, in December.

The friend said speculation the Ristevskis' marriage had been in trouble was not true and described them as "obviously in love".

The couple enjoyed a romantic holiday together just one month before she vanished, with an upbeat Karen messaging the friend a photograph of Borce with a sunburnt nose.

News.com.au obtained screenshots of that final correspondence between the friend and Karen, who affectionately refers to her husband as "Bozza".

Some of Karen Ristevski's final WhatsApp messages before she vanished show she was in an upbeat mood about her husband. The final message on the bottom right is an appeal to Karen sent the day after she vanished.
Some of Karen Ristevski's final WhatsApp messages before she vanished show she was in an upbeat mood about her husband. The final message on the bottom right is an appeal to Karen sent the day after she vanished.
Some of Karen Ristevski's final messages before she vanished, only to be found in a shallow grave almost nine months later.
Some of Karen Ristevski's final messages before she vanished, only to be found in a shallow grave almost nine months later.

According to the source, the blank white square in the first picture, sent via WhatsApp on May 2, 2016, was originally a photo of Borce Ristevski on holiday, his nose red from the sun.

"I'm arriving around 8.30am. Bozza is picking me up xx," Karen messaged the friend on WhatsApp.

The friend replied: "No way! My parents fly out (at) 10 haha so I can pick you up if you want" followed with "I'll be there anyway I think :) gunna drop them off around 8 I think!" and then "Haha no worries ****!"

Karen replied: "To cute **** (sic). Wish mum and dad a safe flight xx".

The insider rubbished claims by Karen's estranged stepson Anthony Rickard that she was having an affair and had planned to leave her husband.

"A week before she disappeared, they nicknamed each other (and) went to dress up parties in matching costumes," the friend said in a message to news.com.au.

Borce and Karen Ristevski. Photo / Facebook
Borce and Karen Ristevski. Photo / Facebook

"The media doesn't show this! I guess the family feels no need to show it, but that's what bugs me, that everyone's making presumptions from (the stepson) and detectives who don't know their family well.

"I'm honest when I say that I'd hang out with (Karen and Borce) and we'd just talk sh*t and have laughs, their marriage was great.

"They were obviously in love! It was the picture perfect family even my own parents admired their family."

The WhatsApp exchange also shows an encrypted message on June 30, 2016, one day after Karen's disappearance, followed by an emotional plea by the friend for her return on July 1, last year.

"Karen if you get this please come back everyone's worried about you!" it says.

When asked if he believed Borce Ristevski was responsible for his wife's death, the family friend said: "I'll honestly say that I believe he's innocent 95 per cent and 5 per cent otherwise, just because I barely know myself and what I'm capable of, not to mention someone else!"

Police have yet to lay any charges over Karen Ristevski's murder but have said they are confident of solving the case, which appears to have stalled in recent days.

On February 22, detectives seized a shovel from the Ristevski family home on which they reportedly found soil traces that matched samples taken from the Gisborne-Macedon area where her remains were found.

Four months later, on June 15, police released CCTV which shows a black Mercedes SLK Coupe believed to belong to Karen Ristevski, travelling along the Old Calder Highway and through Diggers Rest on the day she disappeared.