Nearly 100 tiny threads, blue and grey in colour and so small as to be scarcely visible to the naked eye, have been centre stage at the trial of the alleged Claremont serial killer for several weeks.

Key points: Jane Rimmer and Ciara Glennon were found dead with similar fibres on them

Jane Rimmer and Ciara Glennon were found dead with similar fibres on them Blue fibres were also found on a woman who was raped by the accused

Blue fibres were also found on a woman who was raped by the accused Prosecutors say the fibres came from Bradley Edwards's car and clothing

As state prosecutor Carmel Barbagallo noted in her opening address, "fibre evidence forms a significant part of the case against the accused".

"This evidence comes chiefly from the exacting, meticulous and innovative scientific work undertaken by the expert forensic chemists at ChemCentre."

When the bodies of 23-year-old childcare assistant Jane Rimmer and fledgling lawyer Ciara Glennon, 27, were discovered partially covered by branches in bushland on the fringes of Perth in 1996 and 1997, police finally had a trove of physical evidence they could use to try to solve the Claremont killings.

But there were limitations.

Both bodies had lain out in the open, exposed to the elements for weeks, after the young women went missing — 19 days in the case of Ms Glennon and 55 days in the case of Ms Rimmer.

The young childcare worker's body in particular had suffered from long exposure to rain and wind — typical Perth winter weather — and had also been subject to animal predation.

Ciara Glennon's body was found in Eglinton, north of Perth. ( Supplied: WA Supreme Court )

In both cases, the condition of the bodies made it more difficult for investigators to gather crucial evidence.

But thanks to painstaking work undertaken over two decades by police and scientists at WA's pathology and chemistry labs, significant evidence was recovered.

A cross wrapped in yellow police tape in a bushland setting marking the spot where Jane Rimmer's body was found at Wellard, south of Perth, in 1996. August 1996. ( ABC News )

The evidence included thousands of tiny fibres, many of which were not found until more than 10 years after Ms Rimmer and Ms Glennon were killed.

That work has been laid out in meticulous detail at the trial of Bradley Robert Edwards in the WA Supreme Court in the past few weeks.

Prosecution says fibres link Edwards to victims

Edwards, 51, a former Telstra technician, is charged with the wilful murders of Ms Rimmer and Ms Glennon, as well as a third woman, 18-year-old Sarah Spiers, whose body has never been discovered.

Bradley Robert Edwards has pleaded not guilty to the Claremont serial killings. ( Supplied: WA Supreme Court )

All three women disappeared late at night from the Claremont nightlife precinct in Perth's wealthy western suburbs in 1996 and 1997.

Unlike the DNA evidence, of which there is a single sample apparently connecting Edwards to one of the murders, the fibres evidence is much more plentiful and prosecutors claim it links Edwards to two of the young women's murders.

It also links him to the brutal rape of a teenager at Karrakatta Cemetery in 1995 — a crime which he has already admitted — and potentially links that crime to the murders of both Ms Rimmer and Ms Glennon.

ChemCentre fibre analyst Rees Powell has been on the stand for more than a week in the court, outlining the importance of each of the 98 critical fibres — which had been whittled down from more than 10,000 relating to the case — and how they were examined and compared to the others.

The result was an interconnecting web of matching fibres that the prosecution says puts Edwards squarely in the frame as the killer.

Car, trouser samples are key

The tiny fibres at the heart of the case fall into several broad categories.

Many of them were found in the head hairs of Ms Rimmer and Ms Glennon, both young women with masses of lightly coloured, long, curly hair.

A comparison of blue fibres found on Jane Rimmer's hair and Ciara Glennon's hair. ( Supplied: WA Supreme Court )

Ms Glennon's hair alone contained 50 of these critical fibres and a further 11 were found in the shirt she was wearing.

Most were blue polyester, but there were also blue rayon fibres, grey polyester fibres and both light and dark grey polypropylene fibres.

Ms Rimmer's long blonde locks were also found to contain a host of critical fibres — 22 of them in total, 20 of which were grey polyester, one blue polyester and one blue-grey polypropylene.

The problem was, the source of those fibres was not known at the time.

"And so those fibres were just parked up in the hope that some further evidence would come to light which may give them some significance," Ms Barbagallo said in her opening address.

Fibres connect murders and rape

The first breakthrough came in 2012, when a blue polyester fibre taken from Ms Glennon's shirt was matched to a blue polyester fibre from Ms Rimmer's hair, finally providing an evidentiary link between the murders of the two women.

But scientists still didn't know where the fibres had come from.

By this time, police had linked Ms Glennon's murder to the Karrakatta rape, after a tiny fragment of DNA found underneath the lawyer's fingernails was entered into the state's DNA database and found to match sperm samples taken from the 17-year-old victim.

They believed the man who had brutally abducted and raped the girl was the same man who had killed Ms Glennon.

Examination of the shorts the 17-year-old had been wearing on the night she was attacked had already revealed the presence of one blue polyester fibre and fresh tape lifts taken from the garment in early 2014 then revealed another one.

Meanwhile, the shirt Ms Glennon had been wearing had been sent to the FBI in Washington DC for testing and officers there had scraped debris off it, sending the scrapings back to the ChemCentre, where 11 blue polyester fibres were discovered.

These blue polyester fibres were of the same type as the blue polyester fibres found in Ms Glennon's hair, in Ms Rimmer's hair and on the 17-year-old's shorts.

Link to Telstra car and clothing

Scientists continued their work behind the scenes and soon made another breakthrough.

Mr Rees told the court his team at ChemCentre had noticed the 20 grey polyester fibres found in Ms Rimmer's hair looked as though they may have come from the sort of fabric used in the interior of cars.

Accused serial killer Bradley Edwards's Telstra car was recovered by police. ( Supplied: WA Supreme Court )

They then began an exhaustive search through car wrecking yards and compounds where police kept seized vehicles and in 2014 discovered that the grey fibres matched seat inserts from the 1996 VS series of Holden Commodore.

Now they were looking for a perpetrator who likely drove a particular model of car.

In December 2016 Edwards was arrested and on the same day the car he had been issued by his employer in late April 1996 was seized from its new owner in Chidlow, on Perth's outskirts.

That car was a 1996 Holden Commodore VS series 1 station wagon.

The Commodore was seized by police after being sold to a man in Chidlow, on Perth's eastern outskirts. ( Supplied: WA Supreme Court )

Scientists now had the opportunity to compare their fibres with control samples from the very car driven by Edwards at the time Ms Rimmer and Ms Glennon were murdered.

Mr Rees told the court this week two grey polyester fibres found in Ms Glennon's hair corresponded with control fibres taken from the seat insert material in Edwards's old car, as did the 20 grey polyester fibres found in Ms Rimmer's hair.

Other polypropylene fibres found in both women's hair matched the carpet in the Commodore, he said.

In addition, a forensic search of the Telstra-issue station wagon had uncovered 13 blue polyester fibres in the metal bracket or railing underneath the driver's seat.

After Edwards's arrest, police were able to obtain samples of Telstra clothing worn by its technicians in the mid-1990s — specifically, dark blue-coloured trousers and shorts which were manufactured especially for the telco by Yakka, using a bespoke dye called Telstra Navy.

Exhibit 15190 shows the type of trousers worn by Telstra employees at the time of the killings. ( Supplied: Supreme Court of Western Australia )

Mr Rees told the court the 13 fibres found in the car matched the Telstra clothing, the same type of clothing Edwards would have worn in the mid-1990s.

He said the blue polyester fibres were of the same type found in the rape victim's shorts, in Ms Rimmer's hair and in both Ms Glennon's hair and on her shirt — and all corresponded with the Telstra clothing.

Defence to call own expert fibre witness

Mr Rees is continuing to give his evidence and defence counsel Paul Yovich SC is yet to cross-examine him.

The scientist said this week that some of the fibres found in Ms Glennon's hair also matched a 1997 model Toyota Camry, and had similar properties to a 1996 Holden Apollo and three models of Ford Falcon from 1994 and 1995.

This evidence is expected to be seized on by Mr Yovich, who flagged in his opening address to the trial that "the uniqueness or otherwise of these fibres, whether it can safely be said that they can only have come from the sources the state claims" would be of particular focus.

Possible contamination of the fibres was also raised at the outset by the prosecutor, who said the activities of both Ms Rimmer and Ms Glennon in the hours before their murders may explain how particular fibres came to be found in their hair or clothing.

Additionally, the defence has engaged its own expert fibre witness, further suggesting it disputes Mr Powell's interpretation of the evidence.

The marathon trial, which began in November last year and is being heard by Justice Stephen Hall, is now into its final weeks.

After the fibre evidence wraps up, the prosecution plans to show Edwards's police interview, which spanned some six hours after his arrest, and then it will be the defence's turn to make its case.

Whether Edwards will testify in his own defence remains to be seen.