MATTHEW Williams was being investigated over sending letters that included threats against his former partner and a serving police officer, in the months before he killed Cerys Yemm.

The inquest into Williams’ and Miss Yemm’s deaths was told of seven letters sent to his former partner while he was serving a 27-month sentence at Parc prison, Bridgend.

They contained threats against her and a Gwent Police detective constable and his family, and a suggestion that cars would be damaged.

One described an intention to serve out the sentence, to avoid going on licence when released, thus enabling him to go “under the radar.” A section of the final letter read: “I am going to get away with murder. Trust me. I am too good, too brave, too ruthless.”

The letters were investigated by the Gwent Police Integrate Offender Management Team (IOMT), which monitored prolific offenders.

Team member PC Jake Silver told the inquest the investigation was frustrated as Williams’ former partner refused to get involved in a potential prosecution.

Police had hoped to interview Williams in prison about the letters, but in August 2014 he refused to speak to them.

PC Silver subsequently expressed concerns to the Crown Prosecution Service (CPS) about Williams’ mental health, and formed the opinion that he would be capable of carrying out the threats against his former partner. There was a documented history of incidents “of a domestic nature.”

In late September the CPS concluded that as things stood, there was not enough evidence to charge Williams.

Most of the letters did not contain his signature so more evidence was needed that he sent them, through either handwriting or fingerprint analysis.

The most obvious possible charge would have been over potentially malicious communication, but it was deemed not in the public interest as he was already serving a lengthy prison sentence.

Police began investigating the letters in April 2014.

Lloyd Williams QC, representing the Yemm family, suggested there was a lack of urgency by the police amid an assumption that Williams would remain in prison due to a pending court case, which later collapsed.

PC Silver stated that the CPS had suggested a follow-up discussion on October 21.

But there was no way, he said, that handwriting and fingerprinting analysis could have been carried out between the CPS advice in late September, and Williams being released from prison late in October, a period of around four weeks.

PC Silver said the police were reaching the conclusion subsequently that nothing could be done in terms of recovering other material for handwriting analysis, and they may not be in a position to pursue any analysis.

No further action was taken before Williams’ death on November 6.

In the early hours, barely two weeks after his release, he killed 22-year-old Miss Yemm in his room at the Sirhowy Arms Hotel, Argoed. He later died after being tasered and restrained by police at the scene.

PC Silver maintained that nothing would have gained from arresting Williams over the letters on his release from prison, as he would have been out on bail immediately.

Mr Williams QC said it is “blindingly obvious” from the contents that Williams wrote the letters.

Responding to a question from Mr Williams QC, PC Silver said he did not know if subsequent letters were to be intercepted before sending, or if any were.

He also said he was never told letters were intercepted or that these contained threats - and he would have told the CPS had he known. He added that such evidence might have influenced a future decision to arrest Williams on his release.

Mr Williams suggested the CPS legal advice was wrong.

PC Silver agreed when asked if the police were relying on that advice to proceed.

He disagreed with an assertion made by Nicholas Bowen QC, for the Williams family, that Williams’ former partner was not unwilling to assist.

He also disagreed with Mr Bowen on the question of the speed of the investigation, stating the unit had other offenders to attend to, and that based on the information available at the time, there was no reason to have acted more quickly.

Proceeding.