Crucial DNA evidence found underneath the fingernails of murdered lawyer Ciara Glennon may have got there through laboratory contamination or a chance encounter at a pub she was drinking at on the night of her disappearance, the Claremont serial killings trial has head.
The WA Supreme Court trial of Bradley Robert Edwards for the 1996 and 1997 murders of Ms Glennon, Jane Rimmer and Sarah Spiers has been running for seven months and is in its final days.
Today defence lawyer Paul Yovich resumed summing up his case that Edwards should not be found guilty of the three murders, by homing in on the DNA evidence that is at the crux of the prosecution's case.
The DNA was found on a combined sample of two of Ms Glennon's fingernails, one of which had been mostly torn off.
The trial heard evidence that Ms Glennon's nails were all immaculately groomed, except for two of them, which had been badly damaged in what the prosecution says was a fight for her life as Edwards attacked her with a knife.
But Mr Yovich said the nails could have been damaged while Ms Glennon, 27, was at the Continental Hotel in Claremont on the night she disappeared in March 1997 "if she bumped into someone".
It was a "fraction of a nanogram" of DNA that was found on her fingernails, Mr Yovich said, and it was up to the prosecution to show how it got there.
Contamination by pathologists 'significant': defence
The passage of time and "manifestly imperfect" record-keeping in relation to the fingernail samples at a state pathology lab posed difficulties in relation to the DNA found, he said.
He said given the years that had elapsed, Edwards could not be expected to be able to recall any possible methods of secondary transfer of his DNA, whereby he had contact with someone who then had contact with Ms Glennon on the night she went missing, but this was one possible explanation for its discovery on her nails.
Mr Yovich said the number of times samples relating to the case had been contaminated by PathWest scientists was also significant.
He said the DNA of several different scientists had been discovered on samples, mostly many years after the contamination had taken place, and this contamination had not been detected by PathWest itself but by other laboratories conducting further tests on the samples.
In some of the cases, the scientists had not even touched the samples their DNA was found on, and in one case, DNA from a totally different crime scene had been found on a twig that had been removed from Ms Rimmer's body.
When Justice Stephen Hall asked whether some contamination could be expected given the 23-year span of the case and the thousands of exhibits involved, Mr Yovich agreed it could, but said "it only has to happen once" in a case involving a single piece of trace DNA linking the accused to the crime.
"Contamination events in the laboratory are rare, they're even very rare, but they do happen," Mr Yovich said.
Mr Yovich is expected to wrap up the defence's case next week.
It will then be up to Justice Hall to determine whether or not Edwards is guilty on the evidence presented, a process that could take some months.
