CONVICTIONS in some of WA's highest-profile murder cases may be thrown into doubt following the sacking of one of the State’s leading DNA scientists who was found to have breached testing protocols over six years.

Laurance Webb was a senior forensic biologist with the State-run pathology centre PathWest and worked on dozens of major cases including the unsuccessful prosecution of Lloyd Rayney in 2012.

As well as conducting laboratory tests, he regularly appeared in court as an expert DNA witness for the prosecution in cases that resulted in guilty verdicts.

The conviction of Cameron Mansell in 2011 for the murder of millionaire Perth businessman Craig Puddy is one of 27 cases identified as potentially problematic, as are the convictions of drug dealer Frank La Rosa’s killers that same year.

Play Video Conviction of Cameron Mansell is one of 27 cases identified as problematic Conviction of Cameron Mansell is one of 27 cases identified as problematic

Criminal lawyers said that in light of the revelations regarding Mr Webb’s dismissal, they expected there would be appeals in some cases where DNA evidence had been pivotal in ensuring a conviction.

“The fact that there may be some doubt now about some of the practices that had been employed by PathWest is quite frightening,” Criminal Lawyers Association president Genevieve Cleary said.

“I’m really shocked because DNA is now used in so many prosecutions and sometimes it really is the only evidence.”

Problems with Mr Webb’s work at PathWest were first identified in late 2014 and resulted in him taking extended leave in January 2015 while an investigation was conducted.

That investigation found that allegations of unethical conduct and a failure to follow established protocols were substantiated and led to him being dismissed in August last year.

Despite the inquiry’s implications, PathWest notified the Office of the Director of Public Prosecutions of the outcome only on December 22, four months after Mr Webb was dismissed.

The reason for the delay is not known. But acting DPP Amanda Forrester said an investigation was immediately launched by her office to identify which cases Mr Webb had been involved in.

Letters were sent on Wednesday to criminal lawyers notifying them of the developments.

The letter outlines four breaches of forensic protocols by Mr Webb between 2008 and 2014, including his failure to conduct quality control testing and his recording of quality assurance data when no such testing had taken place.

He had also failed to have his work peer reviewed before providing data to police.

The letter sent to lawyers says a review by PathWest of Mr Webb's work after the breaches were discovered had reportedly not identified any “irregularities” in his tests results.

But lawyers say those claims will need to be independently assessed and, in some cases, evidence would need to be retested to ensure results had not been tainted.

Australian Lawyers Alliance president Tom Percy said the situation was highly unusual, but he did not expect it would result in a “flood” of convictions being overturned.

“While I do not believe there will be an avalanche of cases that will file for reconsideration, there certainly may be some and I would suggest to anyone who was involved in a case that turned on DNA evidence should contact their lawyer to have the matter reviewed,” he said.