After 24 days of DNA evidence being heard in the Supreme Court triple murder trial, it took the states DNA expert Jonathan Whitaker just two hours to reduce the likelihood of the contamination theory to almost negate and very low with Mr Yovich unable to reference another example of a similar contamination having ever occurred in any DNA lab across the globe.

During his testimony Dr Whitaker considered the defences contamination theory, which related to the source of the contamination being either an intimate swab taken from Mr Edwards rape victim, known as HV1, or a sperm cell extract created from the swab, known as 11J7.

He said based on only two DNA profiles being found under Ms Glennons fingernail sample when it was tested in 2008, he could almost negate the swab contamination theory.

I would think its not the case and the reason I say that is that there's no presence of [the Karrakatta rape victim's] DNA in the ultimate fingernail sample," he said.

"I qualify that by saying I cant appreciate or cant accept that there will be a way for [the victim's] DNA to selectively disappear from that swab and for you only to end up with Mr Edwards' in the final result."

And while Dr Whitaker said the sperm extract would not have had the rape victims DNA in it, he considered it extremely unlikely it could have had an opportunity to be spilled in the lab and then been left undetected for 13 months before finding its way into the AJM42 container.

Another difference that I would be alert to is that the extract is now a liquid which is kept frozen in the laboratory and so that needs to be out. It needs to have thawed, he said.

DNA liquid form ... tends to degrade and dry out, so again it needs to have persisted in the environment. It needs to have evaded all our cleaning regimes and controls, etcetera.

Considering that it dried and now becomes a flaky residue, that itself then has still got to get by some mechanism into these pots.

Dr Whitaker said the source, mechanism and opportunity for the contamination to have occurred was very low.

But I stress, we cant say never which is why I positioned it on my subjective scale right down at the bottom end, he said.

Dr Whitaker said if any escaped DNA was present in the lab for 13 months, it didnt contaminate any other exhibits tested in the lab during that time.

Prosecutor Carmel Barbagallo said it was the states case Mr Edwards DNA was found underneath Ms Glennons fingernails because she had fought him in the moments before her murder.

The accused man's DNA has gotten into the mixed DNA profile ... as a result of Ms Glennon scratching the accused man, or otherwise engaging with him in a violent and physical altercation at the time of, or close to her death, she said.

Ciara Glennon

Dr Whitaker agreed Ms Glennons torn left thumbnail on an otherwise well-manicured hand suggested she had inflicted the scratch on her attacker with significant force.

The considerations under that scenario are that Mr Edwards is present at the scene together with Ms Glennon, scratching occurs and that involves force that will promote the transfer of DNA to the nails, that's a one-step transfer which we call primary transfer," he said.

"So comparing and contrasting the pathways, we've got a one-step pathway under the first proposition, but a multiple step pathway under the alternative [contamination theory].

"On the probability of the evidence, if Ms Glennon had scratched Mr Edwards ... I would couch this on my subjective scale as moderately high to high."

During the trial, 10 recorded instances of contamination within the Pathwest lab have been recorded in relation to the 17,000-odd Macro Taskforce exhibits tested over two decades.

Nine out of the ten contaminations were by Pathwest scientists either involved in, or regularly present in the lab, during examination and testing of the samples.

Of the nine occasions, at least seven of them occurred prior to staff having to wear hair nets during DNA testing, and at least four before staff were required to wear face masks.

The increases to personal protective wear required inside the DNA lab grew as DNA technologies advanced and became more sensitive over time.

The only proven example of an unrelated exhibit contaminating a Macro-related item was in 2002, when a twig from Jane Rimmers crime scene recovered the DNA of the female victim of an unrelated crime whose intimate swabs were tested days earlier in the lab.

An investigation concluded the contamination was likely linked to a tube batch which was used for both extractions.

Mr Yovich also referred to a contamination event that occurred in a UK lab in 2007, when an ex-employees DNA was detected on a DNA test negative control blank 16 months after they had resigned.

Justice Stephen Hall.

An investigation into the event concluded while the staff member didnt have access to the DNA lab, she had had regular access to its freezer, as did scientists.

Mr Yovich, during the two times he brought up the incident, failed to mention that it was not known when the contamination occurred, suggesting it had occurred 16 months after the employee had resigned.

Having read the incident report, Justice Hall clarified with Mr Yovich during his cross-examination of Dr Whitaker that the contamination could have occurred while the employee was still in the lab, but was not detected until later.

Dr Whitaker said he was not aware of any example of DNA lasting longer than a year in the lab environment before contaminating an exhibit.

A situation of a staff member in a cold room whose been in there frequently - so DNA might build up and be detected later - is different to a single forensic item that has very little DNA on it appearing over a period of time, Dr Whitaker said.

"We conceive they could happen, but we try to put it under a level of reasoning and rationalism as to whether or not it's probable."

Following Mr Edwards arrest in 2016, DNA testing carried out on his reference sample when compared to the male DNA profile found underneath Ms Glennons fingernails, matched at every loci.

Institute of Environmental Science and Research forensic scientist Susan Vintiner said her analysis of the samples in 2017 found Mr Edwards was at least 80 million times more likely to be the contributor of the DNA profile compared to any other white Australian male not related to him.

Mr Edwards has admitted the DNA recovered from Ms Glennons fingernails matched his profile, but claimed he did not know how it got there.

Mr Yovich, during his opening statement at trial in November, accepted the chance of contamination was remote, but not impossible.

We accept that a scratching event, a direct scratching event of the sort that the state will rely on in proving a connection between the DNA found on these samples and the death of Ciara Glennon is a more likely circumstance, maybe a much more likely circumstance than a chance social contact, he said.

And again, we do not put forward a specific chance, innocent, social contact to explain the DNA.

We accept as well that the chance of contamination in a lab is usually remote although secondary transfer is known and documented in the literature.

But in circumstances where other incidents of contamination are known to have occurred we say, known to have been undetected for some time, your Honour will have to consider just how remote the chance was here and whether it can be safely ruled out even if it was remote.

On the eve of his triple murder trial, Mr Edwards admitted to the 1995 abduction and rape of a 17-year-old girl from Claremont, and a 1988 Huntingdale sex attack carried out on an 18-year-old woman.

He originally pleaded not guilty to the charges and allegedly repeatedly feigned disbelief at his DNA appearing on items relating to the attacks during his police interview, Ms Barbagallo said.

Evidence since heard in his murder trial has revealed Pathwest testing had concluded it 100 billion times more likely the DNA found on the rape victim's pants, and a semen-stained kimono left at the scene of the sex attack, belonged to Mr Edwards than any other person not related to him.

The mammoth murder trial on Tuesday adjourned until March 23, when the state will begin its fibre evidence, which it alleges links Mr Edwards to the murders of Ms Rimmer and Ms Glennon and his Karrakatta rape victim through common fibres found at the scenes.

The fibres allegedly originate from Mr Edwards' Telstra-issued work pants and the upholstery of his 1996 Holden Commodore VS Series I station wagon.

Mr Edwards has pleaded not guilty to the murders of Sarah Spiers, Jane Rimmer and Ciara Glennon.

The trial continues.

Follow WAtoday's live coverage of the trial, here.

Heather McNeill is the crime and courts editor at WAtoday.

The rest is here:

Accused Claremont killer's contamination theory in tatters as state wraps up its DNA evidence with a bang - Sydney Morning Herald