As she wandered between the raised beds last November, police suspect Neill-Fraser spoke to a fellow inmate. The suspected contents of these conversations would, months later, lead to one of the most controversial Tasmanian police investigations in recent history.

Phones were tapped. Prison conversations were bugged. And the woman Neill-Fraser spoke to in the prison garden was charged amid police allegations the inmate had conjured up a plan with an outlaw bikie boss and others to shift blame for a murder from Neill-Fraser to a young, innocent woman.

Neill-Fraser, 62, had been convicted of murdering her partner, Bob Chappell, who disappeared from the couple's yacht when it was moored off the Hobart suburb of Sandy Bay on January 26, 2009.

She is into the seventh year of a minimum 13-year prison term, which could stretch for a decade longer than that if she is denied parole.

It is a matter of great dispute whether Neill-Fraser - a woman convicted despite no body or murder weapon being found - is innocent.

But there is no dispute that as she stood in the Mary Hutchinson Women's Prison gardens, she was desperate.

Either she tended the garden as a cunning murderer, barely halfway through her minimum sentence, who wanted out. Or she did so as a woman wrongly convicted, who had been denied justice by the Court of Appeal and the High Court, and had only one roll of the dice left.

Phones tapped

Tasmania Police were aware that Neill-Fraser's legal team had been busy. But as eminent barrister Robert Richter, QC, and Colin McLaren, a former detective who had investigated the deaths of John F. Kennedy and Princess Diana, set about their task in earnest, detectives in Hobart were far from idle.

The police had received information that the inmate who Neill-Fraser had been speaking to was involved in firearms trafficking.

Since the conversation in the prison garden, this inmate had been released. Police started monitoring her phone conversations.

Before long, they allegedly heard evidence relating to another crime, far more sensational than selling guns to crooks: a conspiracy to pervert the course of justice to free Neill-Fraser.

Police allege that the inmate developed a plan to coerce evidence from the only person who it appeared could set Neill-Fraser free: a troubled young woman named Meaghan Vass.

In the web of circumstantial evidence that had led to Neill-Fraser's conviction for murder - and was, in no small part, woven with lies she had proffered during police interviews - there was one significant hole: why was the DNA of Vass, a homeless 15-year-old at the time of Chappell's disappearance, found on the deck of the couple's yacht, the Four Winds?

Police offered an unlikely and later discredited explanation; someone had stood on Vass's DNA and then stepped onto the yacht's deck. Vass had claimed at trial that she had never set foot on the boat, and did not know how the DNA got there.

But, according to police, the inmate schemed to get Vass to offer a new explanation: she had been on the yacht that night, in the company of known criminals, and had planned to steal from it, before Chappell disturbed them, a fight ensued, and he was killed.

Police could have waited to see if Vass would offer up this testimony to Neill-Fraser's pending court appeal and whether it would be backed up by evidence or demolished via cross-examination. Instead, in a move many lawyers believe was highly controversial, police decided to act immediately.

Detectives applied for warrants to monitor the conversations of Vass and others. Vass, at this stage, was sharing a boyfriend with the inmate, a Devil's Henchman bikie boss called "Sharkie".

As the conversations started to flow, police who listened believed they were recording evidence of a plot to pervert the course of justice and set Neill-Fraser free.

And it got even murkier. Within weeks, allegations emerged that "Sharkie" may be involved in the plan.

Police suspected Vass was under increasing pressure to admit to being on the yacht, clearing Neill-Fraser.

The former inmate was allegedly heard describing Vass to Sharkie as her "little mate". Meanwhile, Vass allegedly confided in her mother that she was under intense pressure to help clear Neill-Fraser. She seemed scared and erratic.

As police built their case, they allege other evidence emerged: the former inmate was allegedly going to be paid $3000 cash, a $40,000 reward and a $50,000 education fund for herself and her children.

It seemed money was being sought to pay a drug debt. It is alleged discussions of cash were intertwined with discussions about making sure it appeared the evidence was legitimate and untainted.

Two other men vital to Neill-Fraser's bid to clear her name were also soon ensnared: lawyer Jeffrey Thompson had, police alleged, pressured another jail inmate to support her case.

On August 9, the police swooped. The inmate who had met Neill-Fraser in the prison garden months earlier was charged with perverting the course of justice and corrupting a witness, with police alleging she would be paid almost $100,000 "in consideration for an understanding that Meaghan Vass be called as a witness, in a judicial proceeding, to provide false evidence". She was also charged with unlawful trafficking in firearms. A week later, Mr Thompson and the other inmate were also charged; both men were alleged to have perverted justice.

It is unclear whether "Sharkie" or Vass will be next, or whether they have been assisting police, but the investigation is ongoing, and further charges are likely. Clubmates of Sharkie either declined to comment or did not return calls, and Vass could not be contacted.

'We simply want the truth'

The charges were seen as a blow to Neill-Fraser's chances of a successful appeal.

Privately, senior police are smarting that her supporters have used the conspiracy charges to back a conspiracy of their own: that the Tasmania Police were motivated by vindictiveness about the never-ending scrutiny of their investigation, and had vowed to strangle Neill-Fraser's last bid for freedom.

The truth, as the force saw it, was far simpler: they were investigating one crime - gun trafficking - and came across evidence of another.

Police say privately they have no concerns that Neill-Fraser was wrongly convicted.

That the witnesses Neill-Fraser was relying on have been charged before they ever had a chance to front her appeal is merely coincidental, police insist. "We simply want the truth here, because there is a lot at stake for some very vulnerable people," one officer said.

But Neill-Fraser's supporters don't buy this. They say police have effectively scared any future witness from helping Neill-Fraser.

While the evidence of Vass was seen as the strongest element of Neill-Fraser's appeal, it was also considered shaky; she was far from a reliable witness.

Still, there is other information that suggests the police case against Neill-Fraser should not be immune from scrutiny. Some of it has been gleaned from an interview McLaren conducted with another former detective - Detective Inspector Peter Powell, who had led the Neill-Fraser investigation.

During the two-hour interview last October, a transcript of which was leaked to Fairfax Media, Powell makes several seemingly telling remarks, including being shocked at Neill-Fraser's sentence and admitting Vass was probably on the yacht, but that he did not know when.

Powell says he discounted that two violent companions of Vass may be involved in Chappell's death because they were drunks. He said if he was running Neill-Fraser's defence during the trial, he would have raised why she was not cautioned as a suspect during her first police interview.

"I mean, I'm the first to say if I was running that defence, I might have run it differently," Powell says.

He agrees that at the time of her first interview, even though police did not consider Neill-Fraser a suspect, her house had been bugged.

And he agrees it is remarkable there was no body, no eyewitness, no known cause of death, no murder weapon, no confession and yet Neill-Fraser was convicted.

He confirms that a man who had lived on the yacht moored closest to the Four Winds, who had a serious criminal history, was not interviewed until after Neill-Fraser was convicted.

Police did not formally interview for weeks - or in some cases at all - several people who were on the banks near where the Four Winds was found sabotaged. Powell says this was because the investigation did not start as a murder probe, and, by the time it was clear Chappell had been killed, Neill-Fraser was the only suspect.

But he says he remains convinced of her guilt, and that she was sunk by her second interview, when the lies she had told in the first were uncovered, and she could not explain them.

Leaving the garden

A brisk half-hour walk down the hill from the prison garden is the Derwent River, and somewhere within its depths likely lie the remains of Bob Chappell.

It may have been a month of explosive developments in a murder case that has had no shortage of drama in the past eight years, but one thing hasn't changed: Sue Neill-Fraser is still tending the garden.

Police have no evidence she is involved in the alleged conspiracy to pervert the course of justice to clear her.

On October 30, she will leave the garden and her four-day appeal will begin. And a case as deep and murky as the Derwent will be dredged for the final time.