A 16-year-old Australian boy has pleaded guilty in the New South Wales Supreme Court to planning a terrorist bombing at the Sydney Opera House, with the attack timed to coincide with the Sydney Marathon — a major road race that uses the landmark as its finish line. The teenager told the court he was radicalised through a social media algorithm beginning on TikTok at age 14, which progressively exposed him to Islamic extremist content and eventually led him to communicate with others on the encrypted messaging app Telegram about carrying out an attack inspired by the 2013 Boston Marathon bombing. He has since expressed remorse and disavowed extremist views; his defence has sought a non-custodial sentence to allow his deradicalisation to continue in the community, while prosecutors argued a custodial term is necessary, with sentencing set for 29 October.