A man has been charged with the murders of two of the women killed in Western Australia's Claremont serial killings.

A 48-year-old Kewdale man has been charged with the murders of Jane Rimmer and Ciara Glennon, WA police said on Friday.

The investigation into the third Claremont murder, that of Sarah Spiers, is ongoing, WA Police Commissioner Karl O'Callaghan said.

The Kewdale man has also been charged with attacks on two other young women, one an abduction that occurred in Claremont before the killings of 1996 and 1997.

Mr O'Callaghan said it would be alleged the man abducted Ms Rimmer, 23, in the early hours of June 9, 1996, after she had been on a night out with friends in Claremont.

The childcare worker's body was later discovered in Wellard, on August 3, 1996.

Police also allege the man abducted Ms Glennon, 27, on March 14, 1997, after she too had been on a night out in Claremont.

The lawyer's body was discovered in bushland in Eglington on April 3, 1997.

As well as those two murders, the Kewdale man has also been charged over attacks on two other women.

He has been charged with the abduction of a 17-year-old in the early hours of February 12, 1995, as she walked through a Claremont park.

"It will be alleged she was restrained and forced into a vehicle and then driven to a cemetery where she was sexually assaulted," Mr O'Callaghan told reporters in Perth.

The man has also been charged with indecently assaulting an 18-year-old woman during a break-in at a Huntingdale home on February 15, 1988.

Mr O'Callaghan said the man allegedly entered the woman's bedroom and attacked her as she slept.

He fled after she struggled, Mr O'Callaghan said.

Mr O'Callaghan said police will allege the man acted alone.

Ms Spiers, 18, is believed to have been the first victim in the Claremont killings. The secretary's body has not been found.

Mr O'Callaghan said there was still much work to be done.

"This has already been the biggest and most complex police investigation in WA history.

"Hundreds of police officers have worked on this case over 20 years."

Mr O'Callaghan said the crimes shocked the West Australian public.