Scientists in the Claremont serial killings case initially only identified a victim's DNA on a critical exhibit, WA's so-called trial of the century has heard.
Bradley Robert Edwards, 51, has pleaded guilty to abducting a 17-year-old girl and twice raping her at Karrakatta Cemetery in 1995, as well as another attack on a sleeping 18-year-old woman at her Huntingdale home in 1988.
But he denies murdering secretary Sarah Spiers, 18, childcare worker Jane Rimmer, 23, in 1996, and solicitor Ciara Glennon, 27, in 1997.
Prosectors say there is fibre evidence against Edwards, and his DNA was allegedly found under Ms Glennon's left thumbnail and left middle fingernail, as well as on swabs taken from the rape victim.
But his defence team claims contamination is an issue.
Scientist Anna-Marie Ashley, from forensic laboratory Pathwest, continued her testimony in the WA Supreme Court trial for a second day on Friday, describing in detail how she performed DNA extractions on Ms Glennon's fingernails.
Ms Ashley said the usual practice was to securely store fingernail exhibits at room temperature.
The clippings went to the DNA lab and some were tested, including AJM42, which is Ms Glennon's left middle fingernail.
Only Ms Glennon's DNA was detected on the sample at that time, the court heard.
Ms Glennon's left thumbnail, item AJM40, was not tested at the time.
The two exhibits are central to the case because when they were tested together years later they allegedly showed Edwards' DNA.
Ms Ashley also testified on Thursday about how she tested exhibits in the rape case.
She will resume giving evidence on Monday.
Australian Associated Press