It is the "what-if" moments during the final hours of murder victims Sarah Spiers, Jane Rimmer and Ciara Glennon that must haunt their families, even more than 20 years later.

What if Sarah had stayed with her friend Emma McCormack on the dance floor of Club Bay View in the early hours of January 27, 1996, and caught a taxi home with her, as Ms McCormack urged?

What if Jane had jumped in the taxi that her friends had commandeered when it slowed down as she stood outside the Continental Hotel on June 9 the same year and they implored her to join them?

What if Ciara's hesitation about joining her colleagues for drinks in Claremont following a St Patrick's Day function at her work in March 1997, had meant she instead headed directly home?

The cruel promise of these alternative scenarios became apparent in WA's Supreme Court at the trial of Bradley Edwards for the women's murders — the so-called Claremont serial killings.

Edwards, 51 and a former Telstra technician, is accused of either forcing or enticing the women into his work vehicle after they left popular nightspots in Claremont, then murdering them and dumping their bodies.

Only the bodies of Ms Rimmer and Ms Glennon have ever been found. Ms Spiers is still missing nearly 24 years later.

The absence of Ms Spiers's body means the defence must rely on circumstantial and propensity evidence and plenty of the former was heard in the court over the past week or so.

Witnesses told the court of seeing a woman matching the petite 18-year-old's description leaning against a bollard near a phone box on Stirling Street in Claremont just after 2:00am on January 27, 1996 — the same phone box Ms Spiers used to call a taxi to take her home.

We heard from the taxi driver tasked with collecting her, who gave a cursory look at the area she asked to be picked up from and, failing to see anyone, kept driving to the nearby Club Bay View where fares were always plentiful.

The 'blood-curdling' screams

And crucially, we heard for the first time from four witnesses who reported hearing "blood-curdling" and "horrible, horrible" high-pitched female screams in the Mosman Park area around 2:30 or 3:00am that night.

Sarah Spiers was last seen on Stirling Road in Claremont on January 27, 1996. ( Supplied )

Ms Spiers had called for a taxi to the riverside suburb of Mosman Park, where she was planning to stay at a friend's house.

The four witnesses lived in different parts of Mosman Park and differed in their accounts of where the screams came from.

Three of them — Jesse-Maree Munro and her partner Wayne Stewart, together with Judith Borratt — thought they had come from a phone box outside a shopping centre on Monument Street, but Robyn Peters, who lived on Palmerston Street, thought they sounded more likely to have come from the direction of the river, or the council chambers.

Ms Munro and Mr Stewart reported seeing the tail-lights of a car from the balcony of their St Leonards Street apartment, parked next to the phone box, although they could not be certain of the make or model, with Mr Stewart describing it as a Toyota Corona.

At the time, Edwards drove a Telstra-issued Toyota Camry station wagon.

Edwards was thought to have been driving this Toyota Camry allocated by his employer Telstra between October 1994 and May 1996. ( Supplied: Supreme Court of WA )

But what if any one of those witnesses, who agreed it was normally very quiet in Mosman Park at that time of night, had reported what they had heard to police?

Screams pierce quiet Wellard night

Screams were also heard in the semi-rural locale of Wellard, in Perth's south, on the night Jane Rimmer disappeared, with resident Ian Sturcke telling the court he "had never heard a scream of that magnitude".

Another resident, Kenneth Mitchell, said he heard the "very traumatic" voice of a woman yelling "leave me alone, let me out of here", followed by abrupt silence.

Again, the sparsely-populated area of Welland was usually very quiet of an evening and hearing screams was definitely out of the ordinary — yet nobody rang police.

Ms Rimmer's body was found five weeks after she disappeared, on August 3, but in another "what if" moment, horse rider Paul Lagenbach found her wrist-watch on the isolated stretch of Woolcoot Road just hours after she went missing and was murdered.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 12 seconds 12 s Police at Wellard, where Jane Rimmer's body was found.

The watch was found just metres from where her naked body lay covered in branches and foliage, and Mr Lagenbach said his horse had "suddenly spooked", sending him tumbling off the animal.

Possibly a little dazed after being dragged along the road a little way before he was able to free himself from the reins, Mr Lagenbach found the silver Guess-branded watch in the middle of the road, exactly parallel to the spot where Ms Rimmer's body lay partially hidden just three or four metres away.

What if he'd walked into the bushes and found her?

And what if the woman who lived nearby and regularly drove down the road had investigated the nasty smell coming from that area of bushes, instead of assuming it was a dead kangaroo and advising her daughter to wind up the windows?

Jane Rimmer was the second of the three Claremont victims to go missing. ( ABC News )

The missing DNA evidence

Ms Rimmer's body was found 55 days after she disappeared, some parts of it in a state of advanced decomposition.

It was winter, and June and July of 1996 had been windy and rainy.

Jane Rimmer's body was dumped in bushland off Woolcoot Road in Wellard. ( Supplied: Supreme Court of WA )

By the time a woman out with her family came across Ms Rimmer's body by chance on August 3 while picking lilies, the DNA evidence that might have been expected to have been found on it had been washed away or otherwise destroyed.

Her clothes have never been found.

Fibres were recovered from her hair, however, and the prosecution says these fibres match those from Edwards' Telstra work car and the clothes he would have been wearing as a technician at the time.

Detailed discussion of these fibres, plus the DNA evidence found on Ms Glennon's body which the prosecution says matches Edwards's, is expected to consume weeks if not months of the trial.

But it is hard not to wonder whether more substantive evidence might have been found on Ms Rimmer's body had it been discovered sooner, and if so, whether that could have been enough to quickly apprehend her killer and prevent Ms Glennon's murder.