Some of the clues that prosecutors say could help solve the Claremont serial killer case are set to be revealed for the first time in court today.

A pre-trial directions hearing, involving lawyers for accused serial killer Bradley Robert Edwards, and the prosecutors who say he murdered Ciara Glennon, Jane Rimmer and Sarah Spiers, will start at 10am in WA’s Supreme Court.

And within it, the first major pointers as to why the State says Mr Edwards is the man WA police have been hunting for more than 20 years are likely to be aired.

It is more than 23 years since Ms Spiers vanished from Claremont on Australia Day 1996 — the beginning of the longest-running and most expensive murder investigation in Australia.

And it has been more than two years since Mr Edwards, a long-time Telstra worker and little athletics volunteer, was arrested and charged with two of the murders that have haunted Perth for decades.

In the string of court dates which have followed, only brief hints of what is contained in the vast bank of evidence compiled by the Macro Taskforce have been revealed by lead prosecutor Carmel Barbagallo.

But the State’s deputy director of prosecutions will today begin arguing before Justice Stephen Hall why she should be able to use so-called “propensity evidence” in the case against Mr Edwards — which will give the clearest picture yet of some of what they have, and how they intend to use it.

The trial is set to be one of the longest, most complex and most watched in WA legal history.

Propensity evidence involves similar facts or acts to those that an accused is on trial for but has not been charged with.

It can go to the accused’s conduct or character.

And under WA law, it is allowed if it is of “significant probative value” to the case.

But first, it has to be agreed to by the judge.

Previous court hearings have been told some of that evidence relates to stories Mr Edwards allegedly wrote or downloaded, which were found on computers at his Kewdale house during a dramatic early-morning raid in December 2016.

But Mr Edwards’ lawyer Paul Yovich has already said he will challenge the use of selective material from the computers, primarily on the basis of relevance.

He also said the date that material was said to have been created, downloaded or accessed would be of “fundamental importance”.

Mr Yovich has also flagged he intends to make a “severance” application, arguing that two of Mr Edwards’ charges be heard separately from the others.

The charges he might apply to have split have not been revealed.

But if and when they are, that is also likely to be an indication of some of Mr Edwards’ defence.

The full trial is scheduled to start in July, and is set to be one of the longest, most complex and most watched in WA legal history.

It is alleged Mr Edwards murdered Ms Spiers, after she had celebrated Australia Day in 1996 at Cottesloe’s Ocean Beach Hotel and then Club Bay View.

Her body has never been found.

He is accused of then killing Ms Rimmer, a 23-year-old childcare worker, who went missing from Claremont in the early hours of June 9, 1996.

Her body was found in bush in Wellard on August 3, 1996.

Camera Icon The Continental Hotel in Claremont. Credit: The West Australian

It is alleged Mr Edwards then abducted Ms Glennon, a 27-year-old lawyer, after she had visited Claremont’s Continental Hotel on March 14, 1997. Her body was found in bush in Eglinton 20 days later. Mr Edwards has denied all three murders.

He has also pleaded not guilty to depriving a woman of her liberty after breaking into her Huntingdale home in 1988 — a charge the court was previously told “encompassed” an alleged indecent assault, and the abduction and rape of a 17-year-old girl in Karrakatta Cemetery in February 1995.

Evidentiary material already includes a trial brief running to tens of thousands of pages, 400 gigabytes of data and about 2500 witness statements.

The trial, which will be conducted without a jury, could run to nine months or longer.

One month of that has been earmarked for examination of what has been described as “the Edwards brief” — including information about where the accused lived, worked and what car he drove.

And DNA evidence is set to play a crucial part in deciding Mr Edwards’ guilt or innocence.

There is a report comprising up to 60,000 pages on DNA material and up to 65,000 pages on hair and fibre evidence, with experts on both sides expected to go head-to-head on what it means.

What today will mean for the families of Ms Glennon, Ms Rimmer and Ms Spiers is another day in court, in the presence of the man police say killed their loved ones.