In the Supreme Court of Western Australia on Thursday, two grieving mothers embraced with tears falling down their cheeks.

Both Carol Spiers and Una Glennon have lost a daughter. Both have watched the hunt for the person responsible ebb in and out of the media. Both have sat in court, metres from the person who was finally accused. And both have spent years waiting to hear a judge say a single word.

"Guilty."

Yet on Thursday, only one of them did.

Supreme Court Justice Stephen Hall found Bradley Robert Edwards guilty of murdering Ciara Glennon, 27, and Jane Rimmer, 23, but acquitted him of killing 18-year-old secretary Sarah Spiers.

All three women vanished while on nights out in the affluent Perth suburb of Claremont between 1996 and 1997. The remains of Ciara and Jane were later recovered in bushland outside the city, but Sarah's have never been found.

The forensic evidence — critically, DNA and fibres — that linked the former Telstra technician to the first two women was lacking in Sarah's case, and Justice Hall said the prosecution had failed to prove guilt beyond reasonable doubt.

Instead, her family must live with a bittersweet concession, a phrase uttered by the judge during his decision: that Bradley Edwards was Sarah Spiers' "probable killer". 

The 51-year-old will face sentencing in December over the two murders, as well as the 1995 rape of another teenager at Karrakatta Cemetery and an earlier assault on a teenager in Huntingdale. 

Meanwhile, Sarah's case remains open.

Jane Rimmer and Ciara Glennon. Images: AAP.

WA Police Commissioner Chris Dawson has vowed to "never give up" the search, and confirmed today that investigators intend to continue questioning Bradley Edwards in prison.

To the murderer, the state's premier Mark McGowan issued a direct appeal from the steps of parliament.

"If you know where Sarah Spiers is, can you please tell us," he told a press conference on Thursday afternoon.

"Can you please provide some closure to the Spiers family to let them know where their daughter is. At times like this, it's the time to do the right thing by the family.

"It's the time to give them some comfort out of all this pain."

The Spiers family has not publicly reacted to the verdict, the promises or the pleas. In fact, those in the room as the decision was handed down on Thursday reported them being stoic as Justice Hall delivered his judgement.

Only once he left the room did they join the families of Ciara Glennon and Jane Rimmer in expressing the emotion of it all. And so, the two mothers embraced, divided by the result but connected in their deep grief.

Ciara Glennon's father also consoled Carol Spiers. According to reporters, he said, simply, "There are no words."

Indeed, the only word Sarah's loved ones need to hear, the only one they deserve, must come from the lips of a judge. 

Feature image: AAP.