A DNA sample obtained by undercover detectives from a discarded soft drink bottle definitively linked the accused Claremont serial killer with the alleged murder of Ciara Glennon, the second day of his trial has been told.

Key points: Bradley Edwards was arrested in 2016, 20 years after Sarah Spiers went missing

Bradley Edwards was arrested in 2016, 20 years after Sarah Spiers went missing He is on trial for three murders — of Ms Spiers, Jane Rimmer and Ciara Glennon

He is on trial for three murders — of Ms Spiers, Jane Rimmer and Ciara Glennon The prosecution outlined how police linked Edwards with the cold case crimes

But this DNA link looms as the key argument that may decide the fate of Bradley Robert Edwards, as his defence opened their argument by targeting prosecution claims about the forensic evidence supposedly linking him to the crimes.

Edwards, 50, is accused of abducting and killing three women — 18-year-old Sarah Spiers, 23-year-old Jane Rimmer and 27-year-old Ciara Glennon — in Perth in 1996 and 1997.

State prosecutor Carmel Barbagallo SC on Tuesday detailed the way police homed in on Edwards in the closing days of 2016, after a cold case review of the case yielded new information.

The review was established in 2013 to try to establish whether there were any crimes in the lead up to the killings that could be linked to them.

The Claremont serial killer victims (clockwise from top) Sarah Spiers, Ciara Glennon and Jane Rimmer. ( ABC News )

A kimono taken from a crime scene in the southern Perth suburb of Huntingdale in 1988 was among the items re-tested as part of the review, and this fresh examination, in November 2016, yielded DNA samples from sperm on the garment.

Ms Barbagallo said this DNA was found to be a match from samples taken from underneath the fingernails of Ms Glennon, which were 80–100 million times more likely to have come from Edwards than from any other man.

The DNA also matched intimate swabs taken from the teenage victim of a brutal rape at Karrakatta Cemetery in 1995.

The kimono from the Huntingdale crime scene was re-tested during a cold case review. ( Supplied )

But she said the DNA did not match any profiles on the national police database.

Detectives then turned their attention more closely to the Huntingdale offence, in which a man had broken into the house of an 18-year-old woman and straddled her as she lay asleep in bed while forcing a cloth into her mouth.

The teenager woke up and was able to fend off the intruder, but not before he left behind a silk kimono and a pair of women's stockings.

Detectives seized bottle from bin, court told

Re-examining the case, police found fingerprints taken from the scene matched fingerprints taken from Edwards when he attacked a social worker at Hollywood Hospital in 1990.

He pleaded guilty to that offence at the time and was sentenced to two years' probation.

Ms Barbagallo said detectives then homed in on Edwards, who was at the time living with his stepdaughter in Kewdale, and put him under surveillance.

Edwards has pleaded guilty to the Huntingdale and Karrakatta Cemetery offences. ( Facebook: KLAC )

When the pair went to the movies on December 19, 2016, undercover police retrieved a discarded Sprite soft drink bottle Edwards had tossed into a rubbish bin in order to obtain his DNA.

This sample matched those taken from Ms Glennon's fingernails, from the Karrakatta rape victim and from the kimono, Ms Barbagallo said.

Edwards pleaded guilty to the Huntingdale and Karrakatta Cemetery offences at a pre-trial hearing last month.

But he denies murdering Ms Spiers, Ms Rimmer and Ms Glennon.

Glennon scratched off DNA in 'fight for her life'

Ms Barbagallo said a mixed DNA sample had been extracted from scrapings taken from two of Ms Glennon's fingernails after her body was found in a bush grave in Eglinton, in Perth's north.

Experts had concluded that the DNA was 80 million to 100 million times more likely to have come from Ms Glennon and Edwards than from an unrelated male and Ms Glennon, she said.

Ciara Glennon fought for her life against her attacker, the Supreme Court was told. ( Supplied )

Ms Barbagallo said the DNA samples found on Ms Glennon fingernails showed that "in fighting for her life, Ciara Glennon scratched or clawed at the accused with her left hand".

This had enabled enough DNA to be left behind and obtained three weeks later, when her body was found.

'Blitz-style' attacks on two victims

Ms Barbagallo said Edwards had no alibi to account for his movements on the night Ms Spiers disappeared.

She said the prosecution's case was that he had taken Ms Spiers from the streets of Claremont, driven her to Mosman Park, where he attacked and subdued her before wilfully murdering her and disposing of her body in an unknown location.

Likewise, Edwards had no alibi on the night Ms Rimmer disappeared, which was just days after he learned his estranged wife was pregnant to her boyfriend — Edwards's former housemate.

It was also 18 months after the Karrakatta attack, by which time she said Edwards "had an established propensity for violence towards women".

Ms Rimmer either willingly got into Edwards's vehicle on the night of June 9, 1996, or was abducted as she walked away from the Continental Hotel in what Ms Barbagallo described as a "blitz-style attack consistent with the manner in which he attacked [the Karrakatta rape victim]".

Ms Barbagallo said at some point during the attack on Ms Rimmer or the disposal of her body, Edwards dropped or discarded his Telecom-issued knife on Woolcoot Road in Wellard.

Some of the fibres found in Ms Rimmer's hair matched fibres from the same make and model of car Edwards was driving at the time, while other fibres matched those used in the manufacture of Telecom-issued shorts and trousers that Edwards wore for work at the time.

On the night Ms Glennon disappeared, Edwards had been due to visit friends at their holiday home in Dawesville, but "unexpectedly" failed to show up until the next day.

Ms Barbagallo said he instead drove to Claremont where he saw Ms Glennon alone and in an intoxicated state on Stirling Highway.

Ms Glennon either accepted a lift from Edwards or, like Ms Rimmer and the Karrakatta victim, was "abducted by him in a blitz attack".

She said he drove her to Eglinton and murdered her, and fibres found in Ms Glennon's hair and on her white t-shirt matched the Telecom-issued pants Edwards wore.

Other fibres also found on Ms Glennon's body "entirely corresponded" with the vehicle Edwards was driving at the time — a white Holden Commodore station wagon which was found by police at a property in Chidlow in December 2016.

Edwards's six-hour police interview

The court also heard evidence about Edwards's early life, some of it from a six-hour police interview conducted on the day of his arrest in which he spoke of his family and his previous relationships.

He "wasn't the best looking guy" at Gosnells Senior High School, he told police, and his glasses were "a bit of a drawback", so he began wearing contact lenses.

He had a girlfriend for a six-week period when he was 15, but had no other relationship until he met his first wife when he was about 20.

That was one of only two significant intimate relationships in his life, the second being with the woman who became his second wife.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 3 minutes 59 seconds 3 m 59 s A timeline of the Claremont serial killings

During that initial police interview, Edwards said he did not frequent the Claremont area, although he had done work for Telstra at the Bankwest branch in Claremont in 2009.

He told police he had "no reason whatsoever" to go driving to Claremont at night.

But Ms Barbagallo said his first wife had kept meticulous records of Edwards's banking transactions from the time, which showed he had accessed banks in Claremont during December 1996.

She said his admissions to the Huntingdale offences, the Hollywood Hospital attack and the Karrakatta rape showed an incontrovertible pattern of behaviour.

"[The admissions] demonstrate a propensity to attack vulnerable women who are effectively strangers to him from behind and without warning, using force to physically restrain them, and using some type of fabric or material in or over their mouths to stifle sounds," Ms Barbagallo said.

DNA the key legal battleground

Defence counsel Paul Yovich SC said a fundamental issue at stake would be that of identity.

He questioned whether or not the only conclusion Justice Stephen Hall could draw was that DNA evidence obtained from Ms Glennon was from Edwards, and whether or not it got there during a struggle.

In a relatively brief opening address, Mr Yovich said DNA material obtained from Ms Glennon was not from "scrapings", as the prosecution had claimed, but from fingernail cuttings.

Defence lawyer Paul Yovich arrives for the start of the Claremont serial killings trial. ( ABC News: Hugh Sando )

He said the mortuary assistant who cut the young lawyer's thumbnail had difficulty doing so because the nail had been torn to the quick.

State forensic laboratory PathWest had determined at the time that material from the left thumb was debris only and "not suitable for testing", yet by 2008 that same material had been deemed fit for testing.

Mr Yovich said many of the scientists and technicians involved in the handling of the forensic material would testify that they could not remember the exact details of the testing, but would describe instead what they "would have done".

This raised doubt about the reliability of the testing.

He said protocols for testing material were "much less sophisticated" in the late 1990s than today, and initial testing of DNA samples from both Ms Rimmer and Ms Glennon had matched male PathWest scientists involved in handling the samples.

Nonetheless, he said Edwards had no explanation for how his DNA came to be linked to Ms Glennon.

Mr Yovich also flagged that cross-contamination would be an issue in relation to fibres found on the bodies of Ms Rimmer and Ms Glennon.

For instance, he said that the jacket Ms Glennon was wearing on the night she went missing, which has never been found, had been thrown on the floor of the Continental Hotel and worn around the waist of a male friend, suggesting fibres could have come from a wide variety of sources.

He said the defence would argue that it could not be proved beyond reasonable doubt that Edwards was the killer, based on any of the evidence presented.