A 16-year-old boy in Sydney has pleaded guilty to planning a terrorist attack after becoming radicalised online, with a court told he intended to bomb the Sydney Opera House during the Sydney Marathon to cause maximum casualties. The teenager, who cannot be named for legal reasons, gave evidence at a sentence hearing describing how he was drawn into extremist content on TikTok from the age of 14, before communicating with others on Telegram about carrying out an attack. The case highlights growing concerns about the role of social media algorithms in radicalising young people, with the boy testifying he initially engaged with historical content before being exposed to increasingly violent Islamic State propaganda.

The court heard the teenager researched targeting the Opera House on marathon day, inspired by the 2013 Boston Marathon bombing, and told an online contact he planned to "test and then do the operation". He said he was only "50:50" on whether he would go through with it, and told the judge he was "deeply sorry" and had since rejected extremist views. His barrister argued for a non-custodial sentence given his deradicalisation while on home detention since November 2024, but the Crown prosecutor said only a custodial sentence was appropriate, citing continued "naivety" in his insight. Justice Stephen Campbell will hand down sentencing on 29 October.