The "particularly graphic and disturbing" evidence to be presented in the Claremont serial killings trial is one of the reasons why it will be heard by a judge alone, rather than a jury, a Supreme Court judge has ruled.

Key points: The Claremont serial killer trial will be heard before a judge, not a jury

The Claremont serial killer trial will be heard before a judge, not a jury Evidence against Bradley Edwards will include videos of two decomposed bodies

Evidence against Bradley Edwards will include videos of two decomposed bodies "Unprecedented" pre-trial publicity also makes a jury trial unsuitable, the judge said

Bradley Edwards, 50, is accused of abducting and murdering 18-year-old Sarah Spiers in January 1996, 23-year-old Jane Rimmer five months later and 27-year-old Ciara Glennon in March 1997.

All three women disappeared from the popular Claremont entertainment strip in Perth's western suburbs.

Mr Edwards is also accused of sexually motivated attacks on two other women in 1988 and 1995.

He denies all the charges against him and is due to stand trial in the Supreme Court in July.

Justice Michael Corboy last year ruled that it was "in the interests of justice" for the nine-month trial to be heard by a judge alone, saying he would deliver more detailed reasons at a later date.

WA Supreme Court Justice Michael Corboy ruled the Claremont serial killer trial should be heard by a judge alone. ( ABC News )

Those reasons have now been published and include the length of the trial and the "extensive and pervasive" amount of pre-trial publicity.

"The events forming the Claremont series did not fade from public memory with the passage of time and they remained the subject of ongoing media and public attention and concern," Justice Corboy said in his reasons, adding that the publicity was "often speculative".

"Some preconceptions and speculations have been so widely and repeatedly disseminated through all the media forums over the many years since the Claremont series that there is a real risk that they have permeated the public consciousness in a way that cannot be adequately addressed by directions to a jury."

Graphic evidence could be 'upsetting to some jurors'

Justice Corboy also listed the nature of the evidence to be presented at the trial as one of the reasons why it was not suitable to be heard by a jury.

In particular, he referenced images of the bodies of the deceased women.

Bradley Edwards is accused of killing (from top) Sarah Spiers, Ciara Glennon and Jane Rimmer. ( ABC News )

"The state foreshadowed that it will seek to produce video and photographic evidence of the decomposed bodies of Ms Rimmer and Ms Glennon in situ, as well as visual material from their post mortem examinations," Justice Corboy said.

"I accept that the characterisation of the material as 'particularly graphic and disturbing' and 'so upsetting to some jurors that they may be unable to objectively consider the relevance and significance of [what] these exhibits depict' is accurate, having regard to the obligations owed by the prosecutor to the court in making this application."

Complexity of evidence cited

Justice Corboy's final reason was the technical or complex nature of expert evidence expected to be presented to the court.

"The likely complexity of expert and forensic evidence to be presented in the trial reinforces the conclusion that the trial of charges alleged against the respondent should be by judge alone," Justice Corboy said.

At a hearing last week, the Judge presiding over the trial, Justice Stephen Hall, indicated that new evidence obtained by the prosecution in the Claremont case threatened to further delay the trial, which is scheduled to begin on July 22.