A double-killer who left a 10-year-old boy an orphan when she murdered his innocent parents has made an extraordinary plea to be freed early so she can return home to New Zealand.

Kim Leanne Snibson was sentenced to 32 years behind bars in 2008 for the 2006 kidnap and murder of Gregory Hosa and Kathryn McKay at her home in the New South Wales town of Nowra.

Snibson is currently not due for parole until 2030, 24 years after she delivered the "slow and painful deaths" of the couple.

Now Snibson, who was dubbed the "face of evil" during trial coverage, has claimed she is "sickened" and "ashamed" for robbing a young boy of his "innocent, good and kind" parents.

Kim Leanne Snibson claims to have found God behind bars.

Daily Mail Australia has published excerpts from Snibson's hand-written plea, part of a legal campaign to reduce her sentence based on current legal principles regarding standard non-parole periods.

According to the NSW Supreme Court judgment at the time, Justice Terrence Buddin found Snibson recruited two accomplices, Stacey Lea-Caton and Andrew Wayne Flentjar, and lured Hosa and McKay to her home, where they were gagged and hogtied before being strangled and suffocated to death.

Their bodies were then bundled into metal 44-gallon drums and driven to Tomerong State Forest, where they were set on fire.

Justice Buddin said he could not determine from the evidence whether it had been Snibson or Lea-Caton who killed the couple (Flentjar was cleared of the murder charges at trial) but found Snibson was the mastermind behind the cruel plan.

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"Each of the victims would inevitably have experienced a slow and painful death," he said.

'We're going to bash them'

Gregory Hosa and Kathryn McKay were pillars of the community, horse breeders who regularly exhibited their shire horses at the Royal Easter Show.

It was through the horses that the pair met Snibson, who looked after horses on their 28ha property.

On January 28, 2006, she lured the couple to her home.

Kathryn McKay, 44, was suffocated with tape. Photo / 7 News

She lay in wait with Lea-Caton and Flentjar, telling the former that their victims were sex criminals who had filmed an assault on her while she was drugged,

"We're going to bash them and tie them up," she told him.

She told Flentjar that they were targeting the couple because of a sexual assault on her daughter.

She provided neither man with proof of the claims and the pair, who had not met before that day, did not have time to compare stories before Hosa arrived at the house after Snibson asked him to come over and discuss the horses.

He was immediately set upon, hogtied and gagged with a sock.

Snibson then called McKay, who was assaulted as she arrived before her mouth was tied with tape.

Flentjar later went home and Snibson and Lea-Caton stayed with their victims.

Lea-Caton would later testify that McKay died first, suffocating after Snibson taped her nose as well as her mouth, leaving her to suffocate.

Snibson then wrapped electrical wire around Hosa's neck, stood on his back, and pulled the wire taut to strangle him to death.

Greg Hosa, 56, was strangled with wire. Photo / 7 News

Their bodies were then loaded into 44-gallon drums that had been stolen from the couple's own property, before they were driven out to the Tomerong State Forest and set ablaze.

Lea-Caton said Snibson returned to the site later that night to add more petrol and ensure that all DNA evidence was destroyed.

But the crime did not go undetected for long, with Lea-Caton going straight to police the following day.

Lea-Caton pleaded guilty to aiding and abetting in the murders and is serving a 22-year sentence.

Flentjar pleaded guilty to kidnapping the couple and has served a 10-year sentence.

'So many beautiful possibilities'

The letter obtained by the Mail reveals a woman leaning on her Catholic faith as Snibson claims to have found God behind bars, while also revealing that she found love with a fellow prisoner.

"I'm in jail for an extremely horrific crime on two innocent, good and kind people who didn't deserve for one second what happened to them," Snibson wrote, saying she has now devoted her life to God.

The scene in Tomerong State Forest. Photo / 7 News

She wrote that she plans to move to New Zealand with her partner, a 42-year-old woman who has served her sentence.

"I think about being home with my family every day, being able to help my mum so her life is a little easier, she's 73 now.

"When we do get to talk , we talk about all the plans I have when come home, back to New Zealand, a new life."

"Over the years in prison, Kim has taken on lots of courses to help sort out her life," her mother wrote in a supporting document.

"Kim was a screwed-up woman at the beginning."

Snibson ended her letter with a promise that the jail term has left that woman in the past.

"Your honour, I'm not the same person that came into jail," she wrote.

"That Kim 17 years ago isn't the Kim I'm going to be when I walk out of jail, she is already gone.

"I have so many beautiful possibilities ahead."

The Crown has opposed any reduction in sentence, submitting that Justice Buddin had been correct in applying the legal principles at the time and the prison term should stand.

Justices Robert Beeches-Jones, David Davies and Peter Hamill will deliver their judgment at a later date.

- Additional reporting, The Daily Telegraph