Natasha Beth Darcy jailed for perverting the course of justice by writing bribes in letters to get off in her murder trial for killing Mathew Dunbar

Natasha Beth Darcy was sentenced in Dubbo District Court on Wednesday afternoon to an extra six months in custody for writing letters to a school friend to bribe her to get her to lie in her murder trial.

Judge Craig Smith handed down his judgement in Dubbo District Court as Darcy - who is serving out her sentence in Clarence Correctional Centre - watched on on video link.

Darcy was given a 25 per cent discount for her early guilty plea to perverting the course of justice.

The court heard how in January 2020 while in custody she wrote two letters to her friend, and also called her, offering money in an attempt for her to give false information in her murder trial to try and get her acquitted.

She was jailed for murdering her then partner Mathew Dunbar by helium asphyxiation after sedating him with a cocktail of drugs in a bid to stage it as a suicide in August 2017.

The court heard Darcy was sentenced earlier this year to 40 years' imprisonment, and wouldn't be eligible for parole for 30 years.

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The defence offered a specialist psychologist report in her defence. Her barrister Nicholas Broadbent conceded there was planning, and "a financial offer which is made", but said there was no threat of violence.

He said there was "evidence of a complex personality" and "issues of attachment" but there was also "impropriety of the blurring of the boundaries" of the friendship.

Judge Smith said the context of the offending during a murder trial was important.

Solicitor for the DPP Andrew Baker said an aggravating factor was that Darcy wanted to inherit Mr Dunbar's multi-million dollar estate.

"The motivation is primarily to acquit her of the murder charge," he told the court, adding it was committed while she was in custody.

Darcy contacted her childhood friend via Facebook messenger intermittently before Mr Dunbar's death and began regular conversations after.

Judge Smith said the offence was not one-off, the money was significant and was sought to achieve an acquittal in the context of her murder prosecution based on false evidence.

He said it was "not overly sophisticated" but "it involved planning, it was not at all spontaneous".

He sentenced her to three years in jail, but only added an extra six months to her non-parole period in custody.

Darcy will now be eligible for consideration for release in May 2048.

A set of agreed facts tendered to the court on her guilty plea revealed Darcy's last-ditch attempt to get away with murder was to write to a school friend in the months before her trial, offering $20,000 or "as much as you need" for a false statement.

Darcy wrote in the letter that she'd been watching an episode of Frasier where a character asked another to lie in court because the opposition was using dirty tactics, but it raised a moral dilemma.

"It got me thinking that is only I could ask somebody to say that Mathew told them he was planning his suicide, maybe a few or several days before he passed," Darcy wrote.

"I'm going to make you a proposition and see if you can be the one to help me."

Darcy wrote a list of details she thought would be sufficient, asking the woman to tell police she spoke to Mr Dunbar for about 40 minutes and that he had said he was planning suicide and had been researching methods.

Darcy wrote that all detectives had on her were extensive web searches and that once someone confirmed Mr Dunbar had been planning suicide, "they have nothing".

She added that friendship was the most important thing and there was no pressure to agree.

The first letter was written in early January 2020 - just months ahead of Darcy's original trial date before it was delayed due to COVID - and was followed by a second letter later that month.

In that note, Darcy wrote she was reminded of a "funny saying" which she recalled went something like "if you're ever in trouble I won't be there to support you, 'cause I'll be next to you helping you hide the body".

The woman received both letters but never replied or spoke about them with Darcy, the agreed statement shows.

She remained tight-lipped on the letters for more than a year but phoned the state prosecuting authority, the DPP, after she saw in the media that Darcy's murder trial had started.

She ultimately gave evidence for the Crown in the trial, which ran for 10 weeks in the NSW Supreme Court in Sydney in 2021.

Both letters were tendered to the court during the trial and their confronting contents were reported at the time.

Tamworth detectives later charged Darcy with acting with intent to pervert the course of justice.

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