Hayley Dodd went missing in from the side of a country road in Western Australia in 1999.

Nearly 20 years after Australian teenager Hayley Dodd disappeared while hitchhiking, her killer has been convicted of murder.

As the judgement was read out in the Supreme Court of Western Australia, Hayley's mother Margaret, who was in the public gallery, placed her hands in a praying position over her mouth and bowed her head.

How her 17-year-old daughter vanished from the side of a country road one afternoon in 1999 had puzzled detectives for more than a decade until 2013, when Perth man Francis Wark became a person of interest.

SUPPLIED Francis Wark raped a hitchhiker eight years after Dodd's death.

Wark, 61, on Monday showed no emotion as he was found guilty by a judge-alone trial of murdering Hayley, but not guilty of her wilful murder.

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Hayley's sister Toni outside court pleaded for Wark to tell the family where her body was.

SUPPLIED Hayley Dodd was 17 years old when she was killed.

"There's no body, we need a body for some closure," she said.

"Tell us where Hayley is so we can put her to rest.

"Give our family some peace, we didn't just lose a sister, we lost parents as well."

WA SUPREME COURT Hayley Dodd's earring as sketched by a friend compared to the actual earring found by police in Wark's ute.

Toni said she hoped Wark received a lengthy sentence which might encourage him to reveal the location of Hayley's body in exchange for a plea deal.

"Maybe he'll tell us where she is... we want to know what's happened and try figure out why," she said.

Wark was convicted after forensic investigators in 2013 re-examined the ute Wark was driving the day Hayley disappeared and discovered a single strand of the teenager's hair in the passenger footwell and her distinctive earring inside the passenger seat covering.

Wark, a convicted rapist, was extradited to Western Australia to stand trial in the Supreme Court of Western Australia over Hayley's death.

THE RUSH TO CREATE AN ALIBI

On July 29, 1999, Hayley was hitchhiking from the town of Dongara to a friend's farm near Moora when Wark lured her into his car, murdered her and disposed of her body within a two-hour window.

Her body and belongings have never been found, except for her earring.

She was last dropped at a location on North West Road about 11am by a woman and spotted by several members of the public walking along the road between 11am and 11.40am.

By 12pm, the sightings had stopped.

Between 11.40am, and 1.36pm that day, Wark picked Hayley up in a Holden ute on the way home from his fortnightly shopping trip, murdered her and disposed of her body before setting off to Perth on his motorbike to meet with friends.

Some time after 11.30am, a driver who pulled over on the Brand Highway because his car was overheating, claimed he heard a female scream in the distance.

By 1.36pm, Wark, who lived on North West Road, was at the Badgingarra roadhouse refuelling his motorbike and paying his account - an alibi the state said he rushed to make.

Prosecution lawyer Amanda Burrows during her opening address said Wark's housemate returned to their property later on the day Hayley disappeared to find his Holden ute, which Wark had driven to the shops that day, was "unusually" parked inside the property's shed and had a broken indicator lever.

Wark had also left a note for his housemate asking the man to chop up some meat he had just purchased from the shop.

"The indicator lever had been broken off and was lying on the floor, indicative, the state would say, of a struggle occurring," Burrows said.

"It is the state's case he was anxious to flee to Perth as quickly as he could... and create an alibi by paying an account on the way."

Wark was later that day involved in a minor traffic accident in Perth and hospitalised overnight.

When the search for Hayley began to gain heavy media coverage in the days following her disappearance, he rang police twice to let them know his whereabouts the day she went missing.

He claimed he was at the shops at Moora, about half an hour's drive from where Hayley was last seen, until around 12pm and did not see her that day.

AN EARRING CAUGHT HER KILLER

Two months later Wark began falsely telling people in the small town he had terminal cancer and was moving to Queensland to be with his family to die.

He sold his property and moved east the following year in early 2000.

In 2007, he raped a Queensland woman he picked up while she was hitchhiking.

The woman was sexually assaulted several times inside Wark's house before she escaped the next morning and ran to a neighbour for help.

The state used the rape conviction as propensity evidence Wark was capable of picking up a hitchhiker and sexually assaulting them.

The state also relied on evidence Wark asked the Queensland woman for her earring.

"He had a tendency to keep a trophy, a trophy of his violent conduct towards women," Ms Burrows said.

In 2013, 14 years after Hayley's disappearance, forensic investigators re-examined the ute Wark was driving the day Hayley disappeared.

They found an earring inside a seat covering matching a sketch drawn by Hayley's friend of the earring she was wearing the day she vanished.

The unique earring was cross shaped and had a blue stone in the centre. Its hook had been damaged.

Hayley's friend drew the sketch on August 2, 1999, remembering the detail of the earring well as she had been with Hayley when she bought it days earlier.

A piece of hair the state alleges belonged to Hayley was also found in the ute's passenger footwell.

A DNA sample from Hayley's lipstick, and her mother were used to determine the match.

Judge Lindy Jenkins found there was no reasonable possibility the earring found in the car Wark was driving belonged to anyone other than Hayley.

She also found Wark had a propensity to pick up female hitchhikers and seriously assault them.

Judge Jenkins found Wark not guilty of wilful murder as she could not determine if he intended to only sexually assault her, or also kill her.

"Propensity evidence and the evidence as a whole satisfies me that the accused has a propensity to use considerable violence against a victim in the course of a sexual assault," she said.

"It does not satisfy me that the accused has a propensity to form an intention to kill to kill for no other reason."

Hayley's mother Margaret Dodd and dozens of friends and family were in court on Monday to hear the verdict.

She wiped away tears as Wark was convicted.

He will be sentenced next Tuesday, January 30.