Almost 24 years since an 18-year-old girl vanished without a trace from a well-heeled suburb of Perth, the trial of the man accused of what became known as the Claremont serial killings has finally begun.

Bradley Robert Edwards is accused of three murders — that of 18-year-old Sarah Spiers in January 1996, 23-year-old Jane Rimmer in June 1996 and 27-year-old Ciara Glennon in March 1997.

He has pleaded not guilty to all three murders.

His trial is expected to take six months and will be one of the lengthiest and most complex in WA history.

Here's what has been revealed so far about the case, including the main prosecution arguments, the key people involved and the likely witnesses.

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

Who is Bradley Edwards?

Until December 2016, Edwards was a Telstra technician living what appeared to be an ordinary, low-key life in suburban Perth.

Married twice, Edwards lived in the working-class south-east suburb of Kewdale and was involved in a variety of local sporting clubs including Kewdale Little Athletics and Central Crocs Football Club.

Bradley Edwards led a quiet life in Kewdale, involved in Little Athletics, before his arrest. ( Facebook: KLAC )

Bradley Edwards receives a 10-year service award for his work at Kewdale Little Athletics Club. ( Facebook: KLAC )

Bradley Edwards with a group of Central Crocs Football Club teammates in 2009. ( Supplied: Central Crocs Football Club )

His anonymous suburban existence came to a sudden end three days before Christmas in 2016, when police raided his house and arrested him.

Initially charged with the murders of Ms Rimmer and Ms Glennon, Edwards was also charged with attacks on two other women, including the violent abduction and rape of a teenager at Karrakatta Cemetery in 1995.

In February 2018, Edwards was additionally charged with the murder of Ms Spiers, whose body — unlike those of Ms Rimmer and Ms Glennon — has never been found.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 4 minutes 48 seconds 4 m 48 s Police commissioner Karl O'Callaghan announces charges over the Claremont serial killings.

He maintained his innocence of all eight charges against him until last month, when he sensationally admitted to five counts relating to the sex attacks on the two women, who have not been named for legal reasons.

Those charges included sexual assault, deprivation of liberty and breaking and entering.

Edwards will be sentenced for those crimes at the end of the murder trial.

What is the case against him?

A series of pre-trial directions hearings and judgments have given an indication of the case against Edwards for the three murders.

DNA and fibre evidence would be crucial to their case.

At a directions hearing in February, the prosecution told the court DNA material found under the fingernails of Ms Glennon allegedly matched Edwards's DNA. It also allegedly matched DNA taken from samples found on the 17-year-old girl who was raped at Karrakatta.

But at later hearings, Edwards's defence lawyers flagged they would argue the material could have been transferred to Ms Glennon through passive social contact, and that they would call their own experts in support of that hypothesis.

Defence counsel Paul Yovich SC said he would also focus on issues of contamination, and would argue that any DNA material obtained was compromised because it had not been treated appropriately by police, technicians and forensic scientists.

The fibre evidence the prosecution said it planned to present concerned common fibres they said were found on the bodies of Ms Glennon and Ms Rimmer, and also on the clothes the 17-year-old was wearing on the night she was kidnapped and raped.

State prosecutor Carmel Barbagallo SC argued during the pre-trial hearings that these fibres came from the work vehicle Edwards was driving at the time, and from his Telstra-issued work uniform.

Carmel Barbagallo will be leading the prosecution case against Bradley Edwards. ( ABC News: Charlotte Hamlyn )

The prosecution also said "emotional upset" would be a key plank of their case — that Edwards committed the rape and the murders at times of significant emotional stress in his life.

Ms Barbagallo stated in previous hearings that she intended to rely on a series of interviews with key people in his life to make her case about the events.

These events included Edwards finding out about his first wife's infidelity, finding out she was pregnant to another man and finalising documents concerning the sale of the marital home.

Mr Yovich has objected to some of this evidence and, in a ruling earlier this month, Justice Stephen Hall said he would provisionally allow the "emotional upset" argument, but would make a final decision during the trial.

What about the defence case?

The pre-trial hearings indicated that identity would go the heart of the defence's case.

The onus would be on the prosecution to prove Edwards committed the murders, while the defence team was expected to concentrate on showing the impossibility of proving beyond reasonable doubt that it was Edwards and no one else who was responsible.

Paul Yovich is defending Bradley Edwards in the Claremont trial. ( ABC News: Charlotte Hamlyn )

Mr Yovich made it plain during pre-trial hearings that he intended to rely heavily on expert testimony casting doubt on the DNA and fibre evidence being connected to Edwards, and on the possibility of samples being contaminated through mishandling.

He also said he would rebut the emotional upset argument by emphasising the lack of evidence proving Edwards's mental state at the time.

What do we know about the evidence?

We already know that some of the evidence will be extremely graphic and likely to shock.

In ruling that the trial should be heard by judge alone and not by a jury, Justice Michael Corboy previously warned that photographs of the deceased women would be "particularly graphic and disturbing".

Graphic evidence of the Claremont victims is expected to be presented to the court. ( Fairfax Media )

This evidence includes videos and photos of their decomposing bodies, as well as material from their post-mortem examinations.

The DNA and fibre evidence is likely to be dense and complicated, involving myriad expert witnesses, and its complexity was another reason it was decided the trial should be judge-alone.

Another piece of evidence is likely to be a knife found on a road not far from where Ms Rimmer's body was discovered in bushland in Wellard, on Perth's southern outskirts.

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

Ms Barbagallo told a pre-trial hearing in February the knife — which carried the logo of Edwards's employer Telecom (now Telstra) — may have been used to kill the 23-year-old.

She said similar knives were found by police at his Kewdale home in a toolbox following his arrest.

Who will be called as witnesses?

The list of witnesses has not been released by the court ahead of the trial.

But thousands of witness statements have already been collected and the number of witnesses giving evidence in court is expected to number in the hundreds.

They are expected to include experts in various scientific fields, some of whom may be flown in from overseas, and possibly other people close to Edwards — family members, friends and workmates.

Police officers who worked on the case during the almost two-decade lifespan of the Macro Task Force — the specialised team set up to solve the Claremont murders — will also likely be called to testify.

David Caporn led the Macro Task Force into the Claremont serial killings. ( ABC )

Most notable among these would be former police Inspector David Caporn, the one-time head of the Macro team who has since retired from the force.

The biggest question will be whether Edwards himself takes the stand in his own defence.

When will the trial be over?

The trial was initially set down to be heard over nine months, but prosecutors have since revised that timeframe down to approximately six months following Edwards's guilty pleas to the rapes, assault and associated charges.

It is possible the case may go on for longer, depending on how long it takes for the witnesses to testify and be cross-examined.

Given the complexity of the case, it could then take months for Justice Hall to arrive at his decision.

Justice Stephen Hall could take some time to hand down his verdict. ( Supplied )

So it could be the latter half of next year before Edwards's fate is known.

After Justice Hall delivers his judgment on the murder charges, Edwards will be sentenced for the five charges to which he has already pleaded guilty.

He will remain in custody for the duration of the trial.