The defendant had become “very angry” after learning of allegations against his grandfather of historic sexual abuse of girls, Mr Mably said.
Jurors were told the grandson had autism which, combined with other emotional and mental factors, diminished his responsibility for the killing.
Due to his condition, he “did not think there was an alternative to killing his grandfather”, Judge Munro said.
In 2016, Ben Oliver was convicted of sexual offences against a young girl when he was aged 15, the court was told.
Ms Munro said this was “learned behaviour from your own childhood”.
His step-dad was “extremely cruel” and physically violent towards him, the court heard.
The man, named only as Steve in court, subjected Ben Oliver “to a sexualised environment”, and introduced him to child pornography at the age of five.
Psychologists appointed by the court described Oliver as “a very damaged man who will require psychological work in the longer term”, Judge Munro said.
In the months before the killing, he had become aware of allegations of sexual abuse against his grandfather, who was also said to have mistreated his wife and had affairs, jurors were told.
His grandmother told him she could not have peace until her husband had died.
The defendant was also depressed and had attempted suicide several times, jurors heard.
Mr Mably said: “He was a troubled and angry young man.”
You must be logged in to post a comment.