New forensic evidence unearthed during a review of the Clydach murders links the man convicted of the killings with a blood-stained sock found at the crime scene, South Wales Police have said.

David Morris was found guilty of murdering Mandy Power, her two daughters, Katie and Emily, and her mother, Doris Dawson, in 1999. Morris died in prison in August aged 59.

Campaigners had spent years calling for his release from prison, attempting to shed doubt on the integrity of the original investigation.

Following a request in 2020 by Morris’s representatives for the release of certain exhibits, the force agreed to appoint an independent senior investigating officer and forensic laboratory to oversee a forensic review of the case material.

Police now say examination of a sock widely accepted as having been used by the offender during the killings identified the presence of a mixed *Y-STR profile that links Morris, or a male relative of his paternal lineage, to the crime scene.

Scientists have said it cannot be determined how or when the profile was transferred on to the sock, but the DNA is more likely than not to be Morris’s.

Operation Dolomite was led by detectives Steve Carey and Ian Ringrose and police forensic expert David Lloyd from Devon and Cornwall Police. The independent forensic science laboratory Cellmark Forensic Services was commissioned to carry out the forensic work.

Morris’s family gave permission for a blood sample to be taken from him after his death on August 20 2021 in order for the tests to be carried out.

Police say accounts provided by two witnesses who featured in the BBC documentary Beyond Reasonable Doubt were also looked into, but the information gathered did not undermine the case against Morris.

Det Carey said: “The outcome of the forensic assessment and completion of further actions have not established any information that undermines the conviction of Morris.

“In my view, as the independent senior investigating officer, the new findings from the samples taken from the sock support the existing evidence that originally convicted him.”

The tragic events that saw the murder of a family-of-four in Kevin Road prompted the largest and most complex police investigation ever undertaken by a Welsh police force.

A unanimous verdict by a jury at Swansea Crown Court in 2002 convicted Morris, but this ruling was overturned on appeal due to a conflict of interest by a defence solicitor.

He was convicted again at a retrial at Newport Crown Court in 2006, when he was sentenced to life imprisonment.

The Criminal Cases Review Commission had reviewed the case as recently as 2018, but at the time found no new evidence and decided not to refer it to the Court of Appeal.

Assistant Chief Constable David Thorne, of South Wales Police, said the reinvestigation did not “demonstrate any lack of confidence in the conviction of Morris”.

He said: “The advancement of forensic technology has provided the opportunity for evidence-based answers to some of the questions which have been raised about forensic issues in this case, along with other matters raised by the BBC Wales documentary.

“Notwithstanding the fact that Morris has been convicted based on overwhelming evidence against him, South Wales Police has shown a commitment to providing evidence-based answers to the issues which have been raised about this case over many years.

“This commitment has now resulted in a forensic link between the convicted killer David Morris and an item of great significance which was recovered from the murder scene.

“South Wales Police commissioned the review in the hope that we could in some way provide closure for those most affected by the murders. In particular, those who lost three generations of the same family and have had to revisit those painful memories time and time again over the last two decades.”