A killer who murdered a woman and then chewed on her face was driven psychotic by drugs, a review has found.
The 34-year-old, who had been serving a jail term for attacking an ex-partner, died after being tasered by police at the scene.
Healthcare Inspectorate Wales has now revealed that Williams had been a drug user since the age of nine, the Mirror reported.
It said Williams was likely to have had a severe reaction to "psychoactive substances" he took, and that he had been offered help to address his addiction but had declined it.
However, the report concluded it was "difficult" to see how the tragedy could have been predicted or prevented by health services.
A post mortem examination on Yemm recorded a provisional cause of death as sharp force trauma to the face and neck.
An inquest into the shop worker's death is expected to take place later this year.