The daughter of Harvey and Jeannette Crewe has urged police to re-investigate the murder of her parents at their Pukekawa farmhouse 40 years ago. Andrew Laxon examines the list of suspects

For a generation of New Zealanders it started as the Arthur Allan Thomas story and became the unsolved mystery of the Crewe murders after Thomas' dramatic pardon.

But for Rochelle Crewe the case has always been far more personal. When she asked police this week to re-open their 40-year-old investigation, she was looking for an answer to a lifelong question; who really killed my parents?

Rochelle was only 18 months old at the time of the double murder in rural Pukekawa, south of Auckland.

Her grandfather Len Demler found her alone in her cot in the family's blood-splattered farmhouse on June 22, 1970.

Police found Jeannette's body two months later in the Waikato River and Harvey's body, with an axle underneath it, in September. Both had been shot.

Arthur Thomas was charged and convicted of the murders and spent 10 years in prison. But after mounting public protest and the personal intervention of Prime Minister Robert Muldoon, he was pardoned in 1979.

A royal commission the following year found the head of the inquiry, Detective Inspector Bruce Hutton, and Detective Len Johnston had planted a rifle shellcase in the Crewes' garden to frame Thomas.

The case has languished ever since.

Solicitor-General Paul Neazor, QC, ruled that the evidence against the two officers was too weak to justify a prosecution and police showed little enthusiasm for pursuing alternative suspects.

So will Rochelle Crewe's plea for justice make a difference? Finding the real killer will be difficult after so many years, as key witnesses have died and most of the forensic evidence has been lost or destroyed by police (to the outrage of Thomas campaigners).

But there has never been a shortage of suspects in this case, credible or otherwise. Here are the arguments for and against the four most prominent contenders:

Arthur Allan Thomas
Local farmer
Convicted 1971, pardoned 1979

Police claimed that Thomas, who was infatuated with Jeannette Crewe, drove to the house at night, balanced on a narrow ledge and used his .22 rifle to shoot Harvey Crewe through an open louvre window.

He then went inside, smashed Jeannette in the face with a rifle butt and shot her dead as she lay on the floor.

There were two crucial pieces of evidence - a shellcase from Thomas' rifle found in the garden four months after the murders and a stub axle found on Thomas' farm tip, which apparently matched the axle found with Harvey's body.

The police case prevailed through two High Court trials (Thomas won a retrial in 1973 but was again convicted), an independent inquiry and several Court of Appeal hearings.

But eventually it fell apart under the scrutiny of dogged campaigners such as scientist Dr Jim Sprott, who proved through an exhaustive analysis that the bullets which killed the Crewes could not have been fired from the Thomas rifle cartridge found in the garden. The two were manufactured at different times and did not match.

The royal commission seized on the implications of this and accused Hutton and Johnston of "an unspeakable outrage" in planting the shellcase to frame Thomas.

The commission was also highly sceptical of the way the stub axle conveniently fell into Johnston's hands when he searched the tip.

The collapse of the forensic evidence highlighted the weakness of the police case against Thomas.

He had no plausible motive as his earlier "obsession" with Jeannette was little more than a passing interest, matched by his pursuit of other local girls.

He also had no opportunity as he was at home with his wife Vivien and cousin Peter on the night of the murders - an apparently rock-sold alibi which failed to convince two juries, to the disbelief of his family and defence team.

The case against Thomas also failed the "mystery woman" test.

Two days after the killings farm labourer Bruce Roddick saw a fair-haired woman outside the house.

It has always been assumed that she fed Rochelle during the five days before the murders were discovered and must have been the killer's accomplice.

The Crown tried to suggest it was Vivien but Roddick later firmly ruled her out.

Len Demler
Jeannette Crewe's father
Died 1992

Demler was the police's original prime suspect. He had a potential motive as his wife Maisie had left half the farm to Jeannette and Harvey in her will and Harvey apparently wanted to buy his father-in-law out.

Demler's behaviour in the aftermath of the murder was certainly bizarre and attracted police suspicion.

According to his own account, when he discovered the bloodstained house he left his 18-month-old granddaughter alone in her cot and went home and cancelled a stock truck delivery to the Crewes. It was his neighbour Owen Priest who rang the police.

Demler refused to join the police search for the bodies of his daughter and son-in-law but quietly shadowed them on horseback.

Senior officers, including Hutton and Detective Inspector John Hughes, put huge pressure on Demler to confess but he refused to crack.

British author David Yallop strongly hinted in his 1978 breakthrough book Beyond Reasonable Doubt? that he believed Demler was the killer and in 2001 journalist Chris Birt openly argued for Demler's guilt.

Although Demler apparently did not have a gun which could fire the .22 bullets used in the murder, Birt argued that the gun in question could fire .22 bullets and that Demler had admitted this to Priest.

Journalist Ian Wishart attacks the theory in his new book Arthur Allan Thomas: The Inside Story, arguing that if Demler had concealed this incriminating evidence, he would hardly admit it to a neighbour after so many years.

He also argues that Demler's anti-social, sometimes chaotic behaviour after the killings does not match the personality of a meticulously organised killer, who removed two bodies from the house without leaving a shred of evidence.

Wishart says police hoped the will would provide a motive but quickly realised it did not. Demler kept his share of the farm for the rest of his life and if Jeannette and Harvey had bought him out, he would simply have had cash instead of the land - hardly a reason for murder.

For similar reasons, Wishart rejects Birt's claim that a woman who is still alive today helped Demler clean the house and feed Rochelle.

He says it seems highly unlikely that this woman would have helped Demler get away with murder, Wishart adds that when Roddick was given the opportunity to identify the woman in a photo line-up he ignored her and picked Demler's daughter, Heather Souter. (Yallop also picked Souter as the mystery woman in a private letter to Muldoon but it turned out she was in the US at the time.)

Jeannette Crewe
Jeannette Crewe, with Len Demler

Journalist Pat Booth, who campaigned for Arthur Thomas' freedom, argues that Jeannette shot her husband and killed herself a few days later. Her father got rid of both bodies in the river.

According to Booth, Jeannette and Harvey were arguing on their wedding anniversary about money.

Harvey attacked his wife, breaking her jaw, and she shot him in retaliation, probably with his .22 rifle, which was never found.

At some stage she contacted her father, who helped her dump the body in the river.

Jeannette then shot herself in despair and Demler got rid of her body, before staging his own discovery of the scene.

Police clearly had similar thoughts when they first arrived at the farm. One reportedly told a reporter; "We're looking for two bodies, one up a tree, the other in the river."

Murder-suicide tends to be the first option investigators consider when a husband and wife are killed and the psychological profile of the murders suggest a crime of passion or revenge.

But as several critics have pointed out, the theory makes no practical sense. Jeannette could not have shot herself because the bullet entered her head at a steep downward angle.

Wishart says it defies credibility to think that Demler would compound his daughter's crime by helping in a cover-up or that Jeannette would take her own life, abandoning her young daughter.

Perhaps the biggest problem with the theory is that Jeannette would have to be the blond woman seen by Roddick outside the house two days after the murder.

At the time Jeannette had a severely damaged skull. It is doubtful whether she would have been walking or even standing normally and if she had, Roddick would have noticed her facial injuries.

Detective Len Johnston
Crewe murder investigator
Died 1978

Wishart argues in his book that Johnston may have killed the Crewes, as well as fabricating evidence to frame Thomas for the crime.

He claims that Johnston was nicknamed "The Fitter" and had a reputation for threats and violence.

Wishart - who admits he has no evidence to support his theory - suggests that Johnston, who investigated a reported burglary at the Crewe's house in 1967, may have realised it was an insurance job, instigated by Harvey.

"Perhaps taking a shine to Jeannette, he confides at some point that he knows Harvey did it to claim the insurance, and that if Jeannette doesn't do him some favours or pay him some money he'll arrange for Harvey to be arrested and maybe even her also.

"Jeannette caves in to avoid the scandal, leading to her increasing fear of being in the house alone."

Wishart suggests Johnston was responsible for two arson attacks on the Crewes' property and murdered the couple when they started to resist his intimidation and blackmail.

He adds that Johnston may have raped Jeannette and then burned the mat on the floor to destroy the evidence.

Wishart says Johnston found the trailer axle later used to help convict Arthur Thomas on the side on the road near the Crewe farm, where five men later said they dumped it. This allowed him to dump the axle with Harvey's body in the river and later frame Thomas by planting the stub at his farm tip.

Even Wishart admits that his theory, which has been dismissed by other commentators, is "entirely speculative" and could be wrong.

He cannot account for the mystery woman, except to speculate that a female criminal acquaintance, such as a prostitute, might have helped. He suggests Johnston could have killed her later to ensure her silence.

Wishart's book also confuses the picture by introducing an unnamed source, who accuses Johnston of intimidation but prefers another suspect.

Wishart briefly develops the idea but then accuses Johnston instead.