It is perhaps Victoria's most baffling murder mystery - six females, aged from 14 to 73, all grabbed seemingly at random in an 18-month period and dumped in scrub. All were on foot when abducted from or near main roads - all but one in broad daylight.

In each case experts could not establish a cause of death and personal items had been removed from the victims, either to conceal identity or to be kept as trophies by the killer.

By the time the first body was found at Tynong North, on December 6, 1980, the killer had struck five times - if, that is, there was only one murderer.

There were several homicide investigations, followed by a taskforce probe, Canadian and US crime profile examinations and two criminal intelligence reviews. More than 2000 people were interviewed, 11,400 pages of notes taken and detailed coronial inquests held.

But no charges were laid. Now police will offer $6 million in rewards, $1 million each, for six unsolved murders in the hope they will uncover information that will lead to the person or persons responsible for the murders of two women whose bodies were found in Frankston and four found in Tynong North.

The head of the Homicide Squad Cold Case Team, Detective Senior Sergeant Peter Trichias, knows that rewards work in seemingly dead-end cases. Just a few weeks ago, the 2008 murder of James Russouw was solved after a reward announcement sparked a call to Crime Stoppers with key evidence: "We hope in this case it will help provide new information."

Trichias says cold cases can be solved when alibi witnesses recant, witnesses decide to come forward or offenders slip up and incriminate themselves. And there is always the chance of an accomplice who may have helped in the cover-up.

But first the facts.

Bertha Miller, 73, the aunt of then chief commissioner Mick Miller, left for church on Sunday, August 10, 1980, intending to take a tram along High Street, Glen Iris. Her body was found off Brew Road, Tynong North, in December 1980.

Eighteen days later Catherine Linda Headland, 14, was heading to catch the bus to the Fountain Gate shopping complex. Her body was found at Tynong North near Miller's.

Ann-Marie Sargent, 18, disappeared after intending to catch a bus to the Dandenong office of the Commonwealth Employment Service and then visit the Clyde post office on October 6, 1980. Her body was found with the remains of Miller and Headland in December 1980.

Police believe the dumping ground was selected by someone who knew the area well.

Narumol Stephenson, 34, disappeared from her car outside a Brunswick flat on November 29, 1980. Her body was found about 100 metres off the Princes Highway, near Brew Road, on February 3, 1983.

Allison Rooke, 59, left her Frankston home to go shopping on May 30, 1980, walking to the nearby Frankston-Dandenong Road to catch a bus. Her body was found on July 5, 1980, hidden in scrub near Skye Road, Frankston.

Joy Carmel Summers, 55, was to have caught a bus on the Frankston-Dandenong Road on October 9, 1981. On November 22, 1981, her body was found in scrub beside Skye Road.

A 1985 review by the Bureau of Criminal Intelligence suggested there were three killers - the sand quarry murderer, the Skye Road offender and another who killed Stephenson.

For this to be correct there had to be two serial killers targeting woman on foot, dumping bodies in scrub who removed personal items and then stopped killing at around the same time. And then just by fluke, seven weeks after the last sand quarry victim was killed, Stephenson was murdered and dumped off Brew Road.

A 1990 re-examination by the same agency rejected the "three killers" theory. "On the balance of probabilities, the same person or persons were responsible for the murders of Allison Rooke, Bertha Miller, Catherine Linda Headland, Ann-Marie Sargent and Joy Carmel Summers." It did not have enough facts to draw conclusions regarding Stephenson's murder.

The review examined several suspects but declared the "best nominated" was Harold John Janman, a former projectionist with a propensity for offering women lifts in his car and with links to both Tynong North and Frankston. But interesting links are not evidence and Janman, now aged 85, has always declared his innocence.

And so what do we know about Janman?

He presents as a deeply religious family man and a prude who would turn "girlie" photos to the wall in the small city projection room where he worked, and yet he had been charged with soliciting for the purposes of prostitution the year before the murders commenced.

It was also around that time, he would later tell police, that "my wife was going to leave me".

He freely admitted that he often offered women lifts on the Frankston-Dandenong Road, where Rooke and Summers disappeared in 1980 and 1981. He agreed to drive with police down the busy road and identify where he invited women into his van. He indicated nine stops, including the two where Rooke and Summers would have been waiting for a bus.

But he was not so forthcoming on every question.

Detective: "Do you know where Skye Road is?"

Janman: "Where sir?"

Detective: "Skye Road."

Janman: "No sir, I have never heard of it."

And yet for years he had worked as a projectionist at the local drive-in just off Skye Road, near where the bodies were found.

Police took him to where the bodies were found. "[He] became nervous and sweated a lot. He walked around the sites as asked, but at no time did he walk in the immediate vicinity of where the bodies had been lying. Extensive areas around the sites had been cleared of bush and scrub by the police crime scene searchers and the investigators stated that without some prior knowledge it would not have been possible to tell exactly where the two bodies had been lying," according to a police analysis.

Three days after the interview and on the anniversary of the discovery of the first body at Tynong, Janman turned up unannounced at the Frankston police station to ask Senior Constable Michael White: "You know I was brought in about two murders in Frankston, well why haven't I been asked about five murders instead of two?"

White: "Which other ones are you talking about?"

Janman: "The ones in Tynong ??? I'm just saying, why haven't they asked about that?"

The trouble was no one, at least publicly, had at that time linked the two murder scenes. No one, that is, except Janman.

According to FBI crime profiler Robert Ressler, serial killers often reach out to investigators: "Some offenders attempt to inject themselves into the investigation of the murder, or otherwise keep in touch with the crime in order to continue the fantasy that started it."

It is a matter of fact that after Janman was interviewed on December 3, 1981, the murders stopped - a fact that may, of course, be entirely coincidental.

Fifteen years after the last body was found, Janman was nabbed in St Kilda when he approached an undercover policewoman and asked for sex. He immediately told police he was "the prime suspect in the Tynong North killings".

Homicide investigators try to find links between where bodies are discovered and the offender, as in most cases killers return to areas they know.

Janman had lived in Garfield, the area adjoining the killer's dumping ground. He had worked at a nearby hotel and was a truck driver whose route took him to the Brew Road sand quarry where three of the victims' bodies were dumped.

In a subsequent taskforce investigation, codenamed Lyndhurst, Janman agreed to two polygraph tests. He failed both.

Janman was not the only suspect in the case. Raymond "Mr Stinky" Edmunds murdered Shepparton teenagers Abina Madill and Garry Heywood in 1966 and is suspected in a series of unsolved rapes and murders, but as he moved to NSW in 1980 has all but been written off in this case.

Distant relatives of Bertha Miller were nominated but investigators from taskforce Lyndhurst discounted them. And there is a new (if unlikely) name. Bandali Debs, who with Jason Roberts was convicted of the 1998 murders of Sergeant Gary Silk and Senior Constable Rod Miller in Moorabbin.

Debs murdered prostitutes Donna Hicks (Sydney) and Kristy Harty (Melbourne), taking both off the street. But he was nominated not by a new witness but by his former crime partner, Roberts, as part of his rejected submission for a retrial.

Police say the abrupt Debs would not have had the cunning to persuade women to voluntarily accept lifts, and other claims made by Roberts against Debs have been proven false.

Trichias says cold case investigators will not just review but reconstruct the investigation. He says his team is keeping an open mind and not concentrating on one suspect: "We hope that someone has information that will help us find the answers."

The six million-dollar question is whether that someone will now make the call.

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