AN 18-year-old who was stabbed and then shot, execution style, and his body covered with branches in the Jenolan State Forest forest west of Sydney is serial killer Ivan Milat's eighth victim, says the former task force commander who led the backpacker murder investigation.

Following Milat's conviction in 1996 for the murder of seven backpackers, police reconsidered dozens of unsolved murder cases to see whether the victims could have been slain by Milat.

But former NSW Police assistant commissioner Clive Small has revised down the potential cases to just one, whose style of killing, burial - and the date of his death - make him a certain victim of Milat's killing spree.

"There was a pattern to the Ivan's killing that had to do with his personal circumstances," Mr Small told news.com.au.

"When he killed he was by himself, or he wasn't in full control of his relationship, or it was falling apart or it had ended.

"With Ivan it was all about control and when Peter Letcher was murdered Ivan had broken up with his partner.

"The other murders [that have been attributed to Ivan] don't fit the pattern."

It was on a Friday in November 1987 that Mr Letcher found himself flat broke and in need of a lift to Bathurst from Sydney.

An unemployed sawmiller, he had travelled to Sydney to propose to his 15-year-old girlfriend, who told him she was too young to get married.

Mr Letcher, one of four children, had lost touch with his family and had not lived at home for the two years before his murder, after losing his job at a timber mill.

"He was as good as gold before he lost his job but he had been a bit of a wayward person after that," his mother, Ann Letcher later said.

He was last seen alive on November 13, when he left Busby in south-western Sydney, saying he intended hitchhiking back home.

Mr Letcher never made it home.

Around the same time, Milat was working for the Department of Main Roads (DMR) as a surface sprayer.

Milat had been charged, but acquitted, of the rape of two young female hitchhikers he picked up near Liverpool railway station in south-western Sydney in 1971.

When that occurred, Mr Small said, Milat was not in a relationship.

He subsequently married a young woman, Karen Duck, but in 1987 the relationship was falling apart.

He had a growing obsession with guns which frightened Ms Duck, and an armoury which included large knives, a pistol, a revolver and a Ruger 10/22 rifle.

He took her on four tours of the remote Belnaglo Forest and once to the Jenolan State Forest, to see a dirt track and a pine plantation.

Ms Duck decided to leave her marriage with Milat, setting off, Mr Small says, the same emotional circumstances which triggered all his killings.

In the days before Mr Letcher disappeared, Milat was working for the DMR in the Jenolan State Forest area, 160kms west of Sydney, and living in south-western Sydney.

On January 21, 1988, two bushwalkers came across Mr Letcher's remains, 15m off a forest trail in a clear-felled section of forest about 20km from the tourist attraction, the Jenolan Caves.

His body was lying face down in a shallow ditch, covered in branches and leaf litter.

He was clad only in jeans, football socks and running shoes.

Nearby lay his shirt and jumper, which were riddled with bullet holes.

The body was badly decomposed and it was only after forensic tests that police discovered the bullet wounds to his head.

Investigating detectives concluded Mr Letcher had been bound and blindfolded, stabbed multiple times in the back and shot five times in the head with a .22 calibre weapon.

A whisky bottle was found at the scene.

Mr Letcher's murder happened two years before the first known backpacker murders were to occur, of Melbourne teenagers, Deborah Everist and James Gibson, who died from multiple stab wounds in December, 1989.

Twenty-six days after their disappearance, British hitchhiker, Paul Onions, escaped from the vehicle of a gun-wielding man on the Hume Highway, 800m north of the Belanglo Forest turn-off.

Milat's other victims were:

• German Simone Schmidl, 20, who disappeared in January 1991, who died from multiple stab wounds, including a knife through her spinal cord.

• Britons Caroline Clarke, 21, who was shot 10 times as if she was target practice and Joanne Walters, who was stabbed.

• German former soldier, Gabor Neugebauer, 21, who was gagged and shot six times and his 20-year-old girlfriend, Anja Habschied, who was decapitated and her spinal cord severed.

Forensic psychiatrist Dr Rod Milton concluded the backpacker killer took great enjoyment out of the killing scene and arranged his victims' bodies like "babes in the wood".

Beer bottles and cigarette butts were found near some of the burial sites and the bodies were placed in shallow graves and covered with branches and leaves.

"After his wife left him, Ivan went off the rails," Mr Small said.

Milat has been named as a suspect in the murders of Sydney nurses Gillian Jamieson and Deborah Balkan, both 20, who disappeared from a Parramatta Hotel in 1980, and many other cases.

"But it's the Peter Letcher case that fits Ivan," Mr Small said.

Police made a search of the area where Mr Letcher's remains were found following Milat's conviction on the backpacker murders, but at the time could find no evidence of any further killings.

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