A new documentary has drawn a fresh link between notorious serial killer Ivan Milat and the unsolved 1972 murder of Melbourne teenager Robin Hoinville-Bartram and the disappearance of her friend Anita Cunningham.

Hoinville-Bartram and Cunningham, both 18, were hitchhiking from Melbourne to Queensland when they vanished.

In November 1972, railway workers found Hoinville-Bartram's body under a bridge on the Flinders Highway, about 250 kilometres west of Townsville. She had been shot twice in the head at close range and was naked from the waist down. Cunningham has never been found.

Milat, who died in 2019 protesting his innocence, was convicted of murdering seven backpackers in Belangalo State Forest, in the NSW Southern highlands.

But many, including detectives who brought him to justice, believe he could have killed scores more.

NSW Legalise Cannabis MP Jeremy Buckingham, who has been using parliamentary mechanisms to probe the true extent of Milat's crimes, told Outback Murder Highway - a four-part series investigating unsolved murders and disappearances along the Flinders Highway - that he believes Hoinville-Bartram and Cunningham could be among the serial killer's earliest victims.

"What we need to do is look at Ivan Milat's life, look at the opportunity he had to commit a crime," Buckingham said.

"Where was he? What was he doing? Were there crimes in those areas at that time that fit his modus operandi? And the answer is yes."

Taskforce Air was established shortly after the first bodies were discovered in Belangalo Forest in 1993.

With Milat yet to enter the police's sights and with few suspects, the task force examined similar unsolved murders nationwide that could have been committed by the same killer.

The previously unpublished list, obtained in parliament by Buckingham, contained 58 names, including Hoinville-Bartram and Cunningham.

Milat was in his late twenties at the time Hoinville-Bartram and Cunningham disappeared.

Jeremy Buckingham MP said the circumstances of the women's disappearance, including their age, the fact they were hitchhiking when they disappeared, and the sexual assault and execution of Hoinville-Bartram, bore striking similarities to the crimes for which Milat was convicted.

Former Queensland detective Brendan Rook pointed out that among Milat's seven known victims were three couples.

"We see a pattern of behaviour where he abducts more couples than he does individuals," Rook said.

"You don't have too many serial killers abducting couples."

Milat's preference for couples was evident decades before the backpacker murders. In 1971, a year before Hoinville-Bartram and Cunningham disappeared, Milat picked up two 18-year-old hitchhikers, assaulted one at knifepoint and threatened to kill the other.

The pair escaped, and Milat was later charged but acquitted.

Buckingham says very little is known about Milat's whereabouts between 1971 and 1974, but he was aware of evidence Milat fled to Queensland after the failed prosecution.

An eyewitness account aired in the documentary adds to the suspicion.

In 2003, witness Merle Whyte told Crimestoppers she met the two women in July 1972 at the Pentland Hotel, 15 kilometres from where Hoinville-Bartram's body was later found.

Whyte recalled seeing the pair socialising with a man they called "Cowboy", before accepting a lift with the man to Charters Towers.

Decades later, Whyte recognised Milat on television as the same man.

Whyte's family claims police dismissed her account. But Buckingham said Milat had a lifelong strange fascination with cowboy attire.

"Who, as an adult, dresses up as a cowboy? Ivan Milat did. He did it his whole life," he said.

Although Milat lived in NSW and his known victims were murdered in the Belangalo Forest, Buckingham said the killer was highly mobile, working at various times on a road gang and as a truck driver in Queensland, and could therefore be responsible for murders across the country.

If proven, Milat's connection to the Flinders Highway will underscore its deadly reputation.

Since the 1970s, eleven people, including Hoinville-Batram and Cunningham, have been murdered or vanished along the remote 900km stretch of road.

Outback Murder Highway, a four-part documentary series investigating a cluster of unsolved murders and disappearances along the Flinders Highway, airs on Nine, which is also the publisher of this website, tonight.

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