Queensland's forensic lab could have tested thousands of crime scene samples more thoroughly, but it decided not to on the back of incorrect advice, an inquiry has heard.
A probe led by Walter Sofronoff QC is examining the lab's 2018 decision to stop testing crime scene samples that contained tiny amounts of DNA.
Queensland Health acting director general Shaun Drummond says he was repeatedly told testing those samples would only result in a DNA profile being matched in about one per cent of cases.
However, that figure was only for cases where samples couldn't be compared with a suspect's DNA, and a later internal review this year found the figure to be closer to five per cent.
"It was never highlighted to myself, or the advice that we gave to the minister, that the one per cent only related to where there was effectively cold-link cases," Mr Drummond told the inquiry on Tuesday.
"That is a fundamentally huge difference in proportionate matters that would have benefited."
A decision to resume processing samples with lower levels of DNA was made in June 2022, three months after Mr Drummond began his current role.
He said even if testing low-level samples had a one per cent strike rate, not testing them wouldn't have sat comfortably.
"The financial impact of resourcing to that level, against the size of our entity, is an insignificant amount of funding," he said.
"It's worked out (that) it's less than a million dollars per annum to be able to carry on the testing at the pre-2018 threshold."
Mr Drummond's evidence follows a decision on Friday to pause tests of some samples over police concerns evidence could be lost.
It relates to the blanket concentrating of DNA, as there could be a risk of exhausting samples on the lower end of the scale, the inquiry was told.
However, the quality manager revealed later on Tuesday she had already changed the lab's testing procedure in August, without being asked.
Helen Gregg, who's overseen quality at the forensic lab since 2006, told staff to seek police approval before exhausting samples taken from crime scenes in August.
She says the QPS made the request, but Commissioner Sofronoff KC rejected that claim.
"That won't do Ms Gregg, because QPS did not ask or did not instruct the lab to seek the approval of QPS, did they? That was your idea," he said.
She admitted the change was her idea, based on her own assumptions after the QPS had asked her boss not to exhaust samples as a standard procedure.
Mr Sofronoff asked Ms Gregg if her decision to give police an effective veto over testing also created a quality issue.
"It could be seen that way I suppose," Ms Gregg replied.
The commissioner said: "But do you see it? I'm asking you."
"I think we're making the best of a difficult situation where we have been asked to not exhaust the sample by the QPS, and we are trying to satisfy that, as well as produce a result for them, and it's not an ideal situation," Ms Gregg said.
The hearing continues with Mr Sofronoff due to hand down his final report in December.
