Mali Bennett-Smith, 17, fatally stabbed 19-year-old Luka Bennett-Smith after telling her he wanted to practise a headlock on her at the home they shared in Bristol in October.
The pair, who were home by themselves at the property in the St Andrews area at the time, had an agreement that Bennett-Smith could practise the grip on her, provided he stopped when she tapped his arm, a court heard.
But on the day in question, he ignored her signal and instead continued to hold her before stabbing her repeatedly.
In a prepared statement he gave to police later, Bennett-Smith said his sister, who had attention deficit hyperactivity disorder (ADHD), was “annoying” and he felt she bullied him.
He told officers: “After watching a video, I went downstairs to the lounge and I asked Luka if I could practise a headlock on her.
“She agreed, we have done this before, and when she needed me to stop we had an agreement where she would tap me on the arm.
“On this occasion I had decided I was not going to stop, I wanted to kill her, I had enough with regards [to how] she had been treating me over the years and recently.”
