A student has been convicted of murdering his 94-year-old step-grandmother three years after an inquest ruled she was the victim of an accidental house fire. Mary Gregory was discovered under a table in the conservatory of her smoke-filled bungalow in Heysham, Lancashire, in May 2018 and died four days later in hospital. An investigation by Lancashire Fire and Rescue Service concluded the most probable cause was a dropped or carelessly discarded cigarette and ruled out any third-party involvement. This led a coroner to later record a verdict of an accidental death. However, police reopened the case in May 2019 after a confession made by Tiernan Darnton, 21, during a counselling session. He said he had killed Gregory – his stepfather’s mother – by setting fire to a curtain at her home. Darnton had made a similar confession several weeks after Gregory’s death, during a game of truth or dare with two friends, Preston crown court heard. “I have a secret I haven’t told anyone. I may have killed someone,” he told the pair. When pressed, he said he started the fire because he did not want Gregory to suffer any longer from dementia, the court heard. He told a counsellor in May 2019 about a friend “who could send me to prison cos of what he knows”. The female counsellor ended the session by saying to him: “I’m not really clear what you’re saying but I think you’re trying to tell me you’ve killed someone,” to which Darnton mouthed “Yes”. A week later he told the counsellor and his stepfather, Chris Gregory, 66, that he had started the fire, the court was told. The counsellor then informed the police. Darnton closed his eyes briefly after the jury foreman returned a unanimous guilty verdict. The court heard that an examination of his mobile phone and laptop found internet searches made after the fire including “I’m a murderer”, “I’m a monster and I’m going to hell”, “I want to cause evil” and “Urge to kill again”. Giving evidence at his trial, Darnton, a former student at Kendal college and Lancaster & Morecambe college, said the case was “all a big misunderstanding” and his confessions were false. He said he only wanted to impress his “edgy” friends in the truth or dare game and felt he had to say something believable, although he knew it was “messed up”. Darnton said his comments to the counsellor were “attention-seeking” and denied saying he had set his step-grandmother’s house alight. He claimed his Google searches were related to his interest in killers and true crime, and said he did not even understand at the time the true definition in law of murder. A fire examination expert for the prosecution said the chances that the fire was caused by a cigarette were “extremely remote”. He said it was most likely started by naked flame ignition near the front bedroom window of the property. The Crown said attempts were also made to hamper any escape by Gregory, with a table placed in front of the conservatory doors, the unplugging of a phone cable and the dismantling of a smoke alarm. A packet of Tunnock’s teacakes and a can of Coca-Cola, bought by Darnton from a nearby service station less than two hours before the fire, were discovered at the scene. Evidence shown to the jury also included drawings found at Darnton’s home address, outlining the floor plan of Gregory’s bungalow. They contained labels including “good hiding place” and “quick exit”, as well as references to needing a “good alibi”. Sentencing will take place on Friday.