A probe into Queensland's troubled forensic laboratory has zeroed in on the lab's failure to obtain DNA from the unsolved murder of a young woman in Mackay.
Potential problems with the lab came to light due to The Australian's podcast series Shandee's Story, about the investigation into the slaying of Shandee Blackburn.
The 23-year-old was stabbed more than 20 times on her way home from work in Mackay in February 2013.
Her former boyfriend John Peros, a champion amateur boxer, was charged with murder but was acquitted in the Supreme Court in 2017.
In August 2020, the coroner found Ms Blackburn died from injuries sustained during an incident involving violence with Mr Peros, who used a bladed instrument.
Her killer remains at large.
The review of the lab's failure to obtain useful DNA from Ms Blackburn's murder is under scrutiny at resumed inquiry hearings into the Queensland government-run Forensic and Scientific Services lab on Thursday.
The hearing was told that despite significant amounts of biological material and blood at the scene of Ms Blackburn's murder and in the car Mr Perros' was driving, the lab could not identify usable DNA.
That issue "has caused significant concern given that it was really from what should be a good source of DNA," counsel assisting Laura Reece said.
Commissioner Walter Sofronoff said it appeared impossible to conclude that the offender's DNA was not on Ms Blackburn's body or clothing.
"And it's not possible to conclude that Ms Blackburn's DNA was not present in the car of the person who had been suspected of the killing."
Environmental factors such as heat, humidity and a shower of rain should not have affected the lab's ability to obtain DNA results.
Forensic Scientist Dr Kirsty Wright believes the failure was due to lab processes rather than any degradation of the samples.
"We regularly get samples from mid-Queensland and north Queensland where the weather is very hot and humid ... and we have been able to obtain profiles even from that kind of environment," she said
"So we're simply left with a question mark over the reliability of these results."
Flaws in the extraction methods and the police collection of evidence were also identified as potential factors in the failure to obtain DNA.
"It is clear that the reporting scientists definitely did not take shortcuts. They really went to the nth degree to try to obtain DNA profiles," she said.
Evidence at the inquiry revealed staff were concerned about testing shortfalls when significant changes to DNA threshold limits were introduced.
The unusual threshold adopted by the lab in 2018 was designed to save money and improve efficiency but resulted in thousands of crime-scene evidence samples not being tested.
The probe has also been told of the toxic environment within the lab and identified management failures at its most senior levels.
Two final days of public hearings have been set down, with Mr Sofronoff's report due within weeks.