A 16-year-old boy has been found not guilty of the murder of nine-year-old Aria Thorpe, who died after being stabbed with a kitchen knife.

Aria sustained a deep wound to her chest at her home in Weston-super-Mare, North Somerset, on 15 December last year.

The prosecution’s case was that the boy stabbed Aria deliberately, intending to kill or cause her serious harm. Alternatively, the prosecution had argued that his action was one that any reasonable person would realise was bound to subject Aria to the risk of physical harm.

Giving evidence at Bristol crown court, the boy said he had picked up a knife from the kitchen of Aria’s home and went into the lounge where she was sitting on the sofa. “Aria stood up and I was waving around the knife,” he told the jury. “Then at some point I decided that I was going to try to make her flinch and scare her, to get a reaction. I leaned forward, acted like I was fencing.

“The knife went into her. Then I pulled it out. I didn’t know what to do. She put her hand to her chest.”

In her summing up, Mrs Justice O’Farrell described it as a “tragic and shocking case” that gave rise to very strong feelings. She said: “He accepts he stabbed with the kitchen knife but he says it was an accident. His intention was to scare her. He held the knife in his hand and lurched or jabbed towards her. He didn’t intend to kill her and did not intend to cause her really serious injury.”

The boy, who cannot be identified owing to his age, denied murder and manslaughter and was cleared of both. After Aria was injured, the boy walked to a nearby train station and told a group of children he had killed her accidentally, the jury was told. He borrowed one of the children’s phones and searched for “what happens if you kill …”.

Another child rang police on 999 and officers attended the station – arresting the boy shortly after he boarded a train. Earlier, Aria had been collected from an afterschool dance class by her mother, Tori Hull. They went shopping for mini-pizzas before Hull left for an evening work shift to earn extra money before Christmas, leaving Aria watching YouTube videos on the television.

Hull told the court Aria had seemed bubbly and happy because she had had a good dance class. “She asked me if she could have the last Oreo after her food and I said yes. She said something like ‘see you after work mummy’. I replied ‘see you after work, love you’.”

A family friend, Ollie Sheppard, who was staying temporarily at the house, returned there after work at about 6pm. He found Aria on the floor of the living room and rang 999, with police and paramedics arriving a short time later.

Andrew Langdon KC, representing the boy, asked how he was feeling about what had happened. “I felt horrible,” the boy replied.

DI Neil Meade, of Avon and Somerset police, said: “Aria Thorpe was a fun-loving girl, adored by her parents and wider family. She clearly brought a huge amount of joy to many people’s lives.

“Aria’s grieving family have shown exceptional courage over the past six months, particularly during this trial, and our thoughts are with them.

“We’d like to remind people that legal restrictions are in place preventing the boy from being named publicly because he is under 18. Nothing should be published that would allow him to be identified.”

The court heard Aria was 4ft 4in tall. The knife was 22cm long and penetrated up to 8cm into her chest.