The sacking of WA's leading DNA scientist for breaching testing protocols is an "unprecedented disaster" in the state's criminal history, Attorney-General John Quigley says.

Key points: Laurence Webb sacked last August after issuing DNA results without peer review

Laurence Webb sacked last August after issuing DNA results without peer review 27 criminals including murderers may be able to challenge convictions: Attorney-General

27 criminals including murderers may be able to challenge convictions: Attorney-General Evidence not compromised, no incorrect results given to police or ODPP: health service

Mr Quigley said Laurence Webb, the senior forensic biologist with the state-run pathology centre Path West, had been dismissed for failing to follow established protocols.

He said Mr Webb's dismissal cast doubt on the convictions of at least 27 people, including those involved in a number of high-profile murder cases.

Mr Quigley said Mr Webb was sacked in August 2016 following an investigations by Path West, but the Office of the Director of Public Prosecutions (ODPP) was not informed of the sacking until two days before Christmas.

Mr Quigley, who became the state's Attorney-General two weeks ago, said he was only told on Monday this week.

He described Mr Webb's sacking as a disaster that would have serious consequences.

"This is as serious as it gets in the administration of criminal justice," he said.

"This is unprecedented ... it is a huge disaster for the administration of criminal justice in Western Australia.

"That this could happen and be kept from the ODPP for so long is of grave concern."

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He said those convicted of murder "may be able to challenge their convictions" and 27 people convicted of a range of offences in a six-year period from 2008 to 2014 — cases that Mr Webb worked on — had been informed of the situation.

"There are many questions to be asked about this and every one of the questions is a serious question with very serious consequences for Path West and some of its officers," Mr Quigley said.

"Perhaps that Path West or somebody else can recover the situation by rerunning all the samples, I don't know.

"But in matters that have already gone before the courts, convicted people may say 'we were denied the opportunity to cross examine the DNA expert who gave evidence at our trial because we did not know of this misconduct'."

System, culture to blame, lawyer says

Lawyers have also expressed their concern.

Former president of the Criminal Lawyers Association Anthony Eyers said he was shocked by the lack of oversight on the laboratory responsible for testing DNA evidence and on Mr Webb.

All cases that rely on DNA evidence should be re-examined, Mr Eyers says. ( ABC TV )

"It's not only a reflection on him, it's a reflection of course on the culture in which he worked and the lack of oversight," he said.

"There really should have been a system is place which would have prevented this happening and someone effectively going rogue without supervision and without others knowing what was happening."

Mr Eyers said Mr Webb's sacking would mean a review of all cases that relied heavily on DNA evidence.

"DNA evidence can be crucial and essential in convincing a jury of the guilt of an accused person, so it needs very urgent examination," he said.

'No incorrect results': health service

A North Metropolitan Health Service (NMHS) spokesperson said Path West had launched a thorough investigation and told the ODPP as soon as it found out about an alleged breach of protocol "in relation to individual results being communicated verbally and by email without peer review".

"Commencing in 2015, the investigation included the review of selected cases over a 15-year period where a court report had been provided by the scientist," the NMHS spokesman said in a statement.

"The review revealed the issuance of non-peer reviewed verbal or emailed individual results did not compromise the validity of the final court report that is used as evidence, thereby no incorrect results were ever communicated to the Police or the ODPP.

"If at any stage of the review and investigation process errors were found, PathWest would have immediately advised the relevant authorities including ODPP etc.

"Any perceived delay in written communication between NMHS and other authorities in relation to the disciplinary matter was due to the requirement to maintain the integrity of a complex investigation."