The judge in the Claremont serial killings trial has agreed to suppress the identity of a man who had an affair with Bradley Edwards's first wife in the 1990s, leading to the birth of a child, months before three women were allegedly murdered.

Key points: The state wants to call evidence from Bradley Edwards's first wife at the trial

The state wants to call evidence from Bradley Edwards's first wife at the trial The court heard her affair began the year before the Claremont murders started

The court heard her affair began the year before the Claremont murders started Jane Rimmer vanished weeks after Mr Edwards allegedly learnt of the pregnancy

The application to suppress the man's identity was made by prosecutors in the Supreme Court after they realised his name had been published last week in a decision by Justice Stephen Hall.

That decision ruled out certain parts of evidence prosecutors had wanted to use at Mr Edwards's nine-month trial, which is due to start in November.

Mr Edwards is accused of murdering Sarah Spiers, Jane Rimmer and Ciara Glennon, who all disappeared from the Claremont entertainment precinct between January 1996 and March 1997.

Sarah Spiers, Ciara Glennon and Jane Rimmer all vanished within a 15-month period. ( Fairfax Media )

He is also alleged to have attacked a woman in her Huntingdale home in 1988 and abducted and sexually assaulted a teenager at Karrakatta cemetery in February 1995.

The identities of Mr Edwards's two former wives had already been suppressed and prosecutor Tara Payne said the state now wanted the identity of the man who conducted the affair suppressed as well.

She said they wanted to "protect the child" who was born out of the affair and was now in their 20s, but who was "an entirely innocent party" in the case.

Pregnancy revealed weeks before Rimmer death

The state wanted to call evidence from the first wife to support an argument that Mr Edwards committed the alleged offences at times of "emotional turmoil and upset" in his life when his "relationships were in decline".

Pre-trial hearings have been told that around mid-1995, Mr Edwards's first wife started a relationship with the man, who had been living with them, and that she then moved out in early 1996.

That timing is crucial because Mr Edwards is accused of abducting and sexually assaulting a teenage girl at Karrakatta cemetery in February 1995, and then abducting and murdering Ms Spiers in January 1996.

Sarah Spiers disappeared on the night of Australia Day and her body has never been found. ( Supplied: Fairfax Media )

The first wife also fell pregnant to the man, and it is claimed she told Mr Edwards in April or May 1996.

Prosecutors say that evidence is relevant because it shows that he was in a state of emotional turmoil around the time Ms Rimmer disappeared a month later in June 1996.

The issue is to be the subject of further legal argument at a two-day hearing in October.

Ms Payne said the proposed evidence of the first wife, including the affair, was likely to be "the subject of much discussion".

Application 'inconvenient', judge says

Justice Hall queried the prosecution about why the application had been made "so late", noting that at an earlier hearing the man's name had been used "at least 35 times" and had been repeated in his judgment last week.

"It is quite frankly annoying and inconvenient to be dealing with it after it has been published," he told them.

Justice Stephen Hall asked prosecutors why the application had been made "so late". ( Supplied )

Justice Hall said he would now amend the judgment to anonymise the man's name.

He urged the prosecutors to give careful consideration to all of the evidence in the case because, "we don't want to be trying to close the door after the horse has bolted".

Justice Hall ruled the man could be referred to as "the former partner of Mr Edwards's first wife", saying that in order to make their reports meaningful, the media needed to be able to refer to the relationship.

Mr Edwards appeared at the hearing via video link from Casuarina Prison.

He was again remanded in custody until the hearing in October.