Detective Chief Inspector John Lehmann from the NSW Unsolved Homicide Squad said a review team was now looking at the files of Milat and other known serial killers Ivan Ashley Coulston, Reginald Arthurell and Bandali Debs.

Other killers known to prey on women will also be looked at as part of the cold case operation, which is believed to be first time police have reviewed known serial killers and all their potential victims at the same time.

“First we gather intelligence on the killers looking for things like where they were at a given time period and if there were any unsolved murders or missing persons around then,’’ Det-Insp Lehmann said.

“Everyone knows about Ivan Milat and his crimes but the other three are equally as evil. They are in that handful of elite psychopaths who seem to have a compulsion to kill.’’

“It's a bit of a departure from the normal way of investigating homicide. Normally you have a victim and then look for a killer.”

The ambitious project is a part of the normal process the squad undertakes regularly.

He cites Bandali Debs, 61, as prime example of a serial killer likely to have murdered more people than the four he has been caught for.

Debs is currently in Goulburn’s Supermax Jail for the murder of Sydney prostitute Donna Hicks in 1995, the murder of Melbourne drifter Kristy Harty in 1997 and killing two Victorian policemen, Rod Miller and Gary Silks in 1998. All of his victims were shot.
“In the ‘60s Debs was living in Sydney when he had a dispute with a man walking his dog. He was only a teenager but armed,” Det-Insp Lehmann said.

“He shot the dog and fired at the owner a number of times as he ran away. If he is capable of that kind of cold-blooded violence as a teenager it's a reasonable assumption someone like him is responsible for more.”

Ivan Milat has long been suspected of killing more than people than the seven backpackers found in the Belanglo State Forest in the early ‘90s.

Coulston has travelled up and down the eastcoast of Australia in the ‘70s and ‘80s before being jailed for the murder of three Melbourne students in 1992.

He was the prime suspect in a number of rapes in Cronulla when he lived there in 1980 and is known to have lived in far-northern NSW’s Tweed area as well.

Arthurell, 69, is currently in Broken Hill jail but is eligible for parole in two months after serving 18 years for the murder of Venet Raylee Mulhall in 1995. He has also been convicted of two other manslaughters.

The Unsolved Homicide Squad has more than 600 cases on its books going back to 1965’s Wanda Beach Murders, of Marianne Schmidt and Christine Sharrock.

Inspector Lehmann stressed the wideranging investigation was at the preliminary stage and was not prepared to link any of the killers to the names of unsolved murders.

“The team will look at what we have in ways of linking these murderers to a victim and then hopefully build up enough evidence to form a strike team and eventually charge them.’’

“Unless we need to get DNA or witnesses statements we avoid telling families of potential victims of the investigation until we believe we have to or are in a position.

“We don’t want to raise their hopes or bring up those emotions unless we have to.’’

All four are currently in jail, and except for Artherall have little chance of ever getting out.

“Even though many of the murders are old, sometimes 30 years ago and the killers are locked away it doesn't mean we should give up,” he said.

The brutal killings of flatmates Kerryn Henstridge, 22, Anne Smerdon, 22, and Peter Dempsey, 27 made Ashley Coulston infamous but, despite violent flare ups throughout his life, he first came to the public attention for more benign reasons.

A keen sailor, in 1988 he designed and built his own craft and tried to sail across the Tasman to New Zealand in Australia’s smallest boat, G’Day 88.

After 46 days at sea in stormy conditions, he set off the emergency beacon and was rescued by a passing tanker.

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Before the voyage, those he knew described him as a quiet loner but he enjoyed the attention his adventure afforded him, according to the Herald Sun.

But there were several red flags in Coulston’s childhood that hinted at the depraved slaying that would follow.

He struggled to read and write at school in the north of Victoria and only found friendship with younger children — but it was his temper that concerned former teacher Tony Shelper.

“He couldn’t cope and out of sheer frustration he would be ready to kill,” Shelper said. “It wasn’t rare for him to rip his shirt off in the classroom and have the buttons fly off. He’d smash rulers and pencils.”

More worryingly, at the age of 14 he broke in to the home of two female schoolteachers and forced them to drive across the border to NSW at gunpoint before a truckie came to the women’s rescue.

Coulston lived in Sydney for most of the 80s before moving back to Melbourne in 1989.

Three years later the three flatmates advertised for a fourth flatmate. Coulson answered the ad and bound the three with cable ties before executing each of them with a single shot to the back of the head.

He has been jailed for life with no hope of release.

To the outside world, he seemed a pillar of the community, a helpful handyman living in suburban Melbourne.

But behind the facade, Bandali Michael Debs — known to everyone as Ben but born Edmund Plancis — was a sociopath with a long criminal history.

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As well as a series of violent infringements in the mid-90s, police believe Debs committed a series of armed robberies with his nephew between 1991 and 1994.

During these robberies, most of which occurred in restaurant, police believe he pistol-whipped a woman, shot a man and fired at two officers but missed, in a grim warning of what was to follow.

In 2003, he was convicted of the cold-blooded murder of Sgt Gary Silk and Sen-Constable Rod Miller at Moorabbin, Victoria in 1998. Police then matched a DNA sample from the unsolved murder of drifter Kristy Hardy, with Debs convicted of her murder.

The officers were attempting to intercept Debs and criminal partner Jason Roberts in a Chinese restaurant when Debs gunned them both down.

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He was later convicted of killing prostitute Donna Hicks in the NSW Supreme Court in 2011 when Police Association secretary Greg Davies described Deb as the “personification of evil.”

A newspaper report in 2003 saw Debs’ brother claim the pair were tortured as children including being whipped with copper wire.

The story of his slaying of the officers formed the basis for Underbelly Files: Tell Them Lucifer Was Here, broadcast on Channel 9 in 2011.

The bodies were found over the course of a year in various state of decay in the Belanglo State Forest.

Key to the conviction was British backpacker Paul Onions who Milat threatened with a revolver in 1990. Onions managed to escape, returning to Australia to help with the investigation years later.

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Many of the facts around Milat’s early family life are unclear but relatives have played a big part in his story.

Firstly, during his trial, Milat’s defence team tried to pin the blame on other family members, particularly his brother, Richard.

Then, in 2010, his great-nephew Matthew Milat and his friend Cohen Klein brutally murdered David Auchterlonie on his 17th birthday with an axe in the same forest, with Klein filming the horrifying attack. They were sentenced to 43 and 32 years in prison respectively in 2012.

A man of many identities Reginald Kenneth Arthurell was a drifter with the ability to adjust to a variety of situations without standing out — despite his 2m frame.

He was known as Robert when working as a hotel chef and called himself Tex at outback rodeos, wearing a cowboy hat despite never having ridden a horse.

Arthurell drifted from town to town before becoming the prime suspect in the murder of 82-year-old Catherine Page in her hometown of Coonamble in central west NSW in 1971.

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The town was devastated by floods and Arthurell, then 25, was stranded there.

He already had a number convictions, including one for possessing an unlicensed pistol. He also once tricked police by dressing as a woman to evade capture. The case is unsolved.

Three years later, while visiting his mother in Sydney, he met his ex-step-father Thomas Thornton. The pair ended up back at Thornton’s Guildford home where the older man was found stabbed to death.

In 1981 he was charged with the murder of sailor Ross Browning, 19, in the Northern Territory in a town called Three Ways near the junction of the Barkly and Stuart Highways.

The sailor had given him and another man a lift in his brown Holden station wagon with a green box trailer on the back.

They threw various items of property out of the vehicle as they left the territory and drove into Queensland.

Arthurel pleaded guilty to manslaughter, meaning the murder charge was dropped.

He served six years of a 12 year sentence in Darwin before being released. NSW detectives extradited him to Sydney where he pleaded guilty to the manslaughter of his stepfather, arguing that he was provoked.

He was then released again, this time on parole, but was ordered to live with Christian prison visitor, Venet Raylee Mulhall, 54, who had started writing to him while he was in jail in Darwin.