Lewis Dale guilty of murdering grandmother Irene Dale
A teenager has been found guilty of the murder of his grandmother and the attempted murder of his grandfather in an attack "like the film Psycho".
Irene Dale, 78, and husband Allan, 80, were stabbed in bed at their home in Summergangs Road in Hull last April.
Their grandson Lewis Dale, 17, who lived with them, admitted killing her but denied murder and attempted murder due to diminished responsibility.
He will be sentenced at Hull Crown Court later this month.
Dale had told the court he regularly used the drug mephedrone, also known as M-Cat, and could not remember attacking his grandparents.
The jury was told Mr and Mrs Dale had gone to bed at about 22:30 BST on 26 April.
Later that night Dale entered the couple's bedroom and stabbed his grandfather in the chest.
Mrs Dale woke up during the attack and her grandson stabbed her several times before running from the room.
Mr Dale told the jury his grandson had behaved like the character Norman Bates from the Alfred Hitchcock film Psycho.
He told the jury: "I know it was Lewis but I can't understand it, why it happened."
Speaking outside court after the verdict, Det Ch Insp Alistair McFarlane, who led the investigation, said the case had been "harrowing for the family".
"This has been a horrible crime, it's been terrible to investigate and Lewis Dale is going to go to prison for quite a long time.
"Although Lewis Dale has, ultimately, been brought to justice, it has brought no satisfaction to me.
"I really feel for the family as they continue to come to terms with what has happened."