A ST Dogmaels woman has been found guilty of murdering her mother.

Penny John, of Maes Dre, Union Terrace, St Dogmaels, and her son Barry Rogers, of High Street, Fishguard, were convicted on Tuesday afternoon of murdering John’s mother and Rogers’ grandmother, 84-year-old Betty Guy, at her home in Johnston in 2011.

John, 50, and Rogers, 33, were told immediately that at the sentencing hearing on Thursday morning they will receive life sentences.

The only question to be decided, said the judge, was the minimum number of years they must spend in jail before being allowed to apply for parole.

Rogers held his head in his hands and wept after the jury forewoman announced the unanimous verdicts.

John sat stony-faced and showed no emotion.

John was remanded in custody until the sentencing hearing. Rogers has been in custody throughout the trial at Swansea Crown Court.

The judge, Mr Justice Lewis, praised the jury for carrying out their duty “magnificently” and described the case as having been emotional and complex.

He said he would study sentences passed by other judges for mercy killings before deciding on the minimum terms.

He will also listen to pleas of mitigation by the couple’s barristers.

Rogers and John killed Mrs Guy - his grandmother and her mother - because she was too old and suffered from ill health, the court was told.

John mixed sedatives - including her own sleeping tablets - with whiskey and gave the mixture to her mother in the early hours of 7 November 2011.

That failed to kill her and Rogers, a former soldier, “finished her off” by placing a pillow over her face.

At first her death was believed to have been from natural causes and Mrs Guy’s body was cremated at Narberth just four days later.

But Rogers could not keep his mouth shut and over the coming years told various women, including his one-time wife, that he and his mother had killed her.

After they had been arrested detectives devised a clever plan to trap them.

Although they were living at different addresses police agreed to grant them bail as long as they both stayed at John’s home in Maes Dre, Union Terrace, St Dogmaels.

Officers drove them to the address to make sure they abided by the bail conditions.

By then a listening device had been placed in the property and as soon as they walked through the door they began talking about what they had done.

It was five years after they had killed Mrs Guy and neither could remember if they had swapped mobile telephone text messages that the police might be able to retrieve.

Rogers became worried his mother was “starting to crack” and urged her to stick to their story that Mrs Guy had died from old age. But the jury saw through it.