A Commission of Inquiry into Forensic DNA Testing heard on Thursday that senior officers in charge of the police DNA unit had only a limited understanding of DNA testing.
Superintendent Dale Frieberg, Operations Commander of the Forensic Services Group, told the inquiry she didn't have scientific qualifications and didn't understand the testing changes proposed by the Forensic and Scientific Services lab.
The lab introduced changes to DNA threshold limits to save time and money and improve efficiency, which meant that from early 2018 thousands of crime scene samples weren't tested.
"I wouldn't have understood it the way in hindsight I should have understood it," Supt Frieberg admitted to the inquiry.
Documents tendered to the commission show Supt Frieberg agreed with the changes, which she told the inquiry had been influenced by advice from Queensland Health.
"I guess as part of my role as a superintendent, and you know, in any government department, it's about relationships," she said.
"It's about trust.
"We (the Queensland Police Service) paid $3 million a year to Queensland Health to provide us with expert advice ... the options paper has come from people who are experts, and I trusted that advice."
The $3 million was part of the annual police budget for forensic laboratory services, the inquiry was told.
Supt Frieberg said she wasn't the "ultimate decision maker" and her assumption was that there would be further consultation before the DNA threshold changes were implemented.
However, former Forensic and Scientific Services lab executive director Paul Csoban said staff held a number of meetings with police and he believed they understood the testing changes.
"They seemed to understand the changes, and there was no great pushback on it," Mr Csoban said.
The decision to accept the changes was ultimately a Queensland Police Service decision, he added.
"I believe that this was a matter for a QPS decision, it was not a matter for Queensland Health to make that call and I say this because, very frequently, we were told that the police had the final say on the samples and how they were treated and what was being tested."
The probe into Queensland's DNA scandal was sparked by the release of an interim report identifying serious shortfalls in testing thresholds.
More than 21,000 evidence samples, including almost a third from murder and rape scenes, collected between 2018 and 2021 were ruled "insufficient DNA for testing" and never fully examined, the inquiry was told earlier this week.
Investigators relying on the lab results routinely asked for further testing on major crimes after testing failed to identify any DNA profile.
Senior police were so alarmed by the repeated testing failures a formal request was issued for the threshold limits to be formally reviewed.
Managing scientist Cathie Allen and team leader Justin Howes, who pushed for the changes, were stood down after the interim findings were released.
The hearing continues before Commissioner Walter Sofronoff in Brisbane ahead of the commission's final report due in December.
