A UK teenager pleaded guilty to planning an Isis-inspired terrorist terrorist attack in Cardiff, Wales on the same day as a Justin Bieber concert. The 17-year-old, whose identity cannot be revealed because he is a minor, wrote a “letter of martyrdom,” as well as a cartoon note such as “to run over unbelievers with a car” and “to attack the infidels who oppose Allah in the neck.

He was indicted on five counts of terrorism-related charges at Birmingham Crown Court after his arrest on June 30, a month after an attack in Manchester Arena killed 23 people and injured more than 500 during a concert by Ariana Grande, according to The Guardian. He was arrested after investigating security at a Bieber concert at the Principality of Cardiff stadium.

The defendant is white and British

When the police raided the boy’s house, they found a hammer and knife to gut in his school bag, as well as a suicide note that read: “I am a soldier of the Islamic State. Today I attacked Cardiff because his government continues to bomb targets in Syria and Iraq. There will be more attacks in the future.”

According to The Guardian, he also had searches on the 17-year-old jihad website and “vehicle mounting pavement – car ploughs through a crowd,” as well as several possible targets in the city. Among those objectives could have been the Principality Stadium, as he also sought information on the Bieber concert scheduled for 30 June, including the term “Justin Bieber security”. He also looked up the phrases “how to steal a car” and “how to steal a car from an unbeliever” and visited a website that details how to kill someone with a knife.

The defendant denied plans to carry out a terrorist attack and instead, his lawyer argued that he had a “stupid interest in the bloody one,”according to the BBC. The boy told the jury that he did not own a Koran and was only curious about how easy it was to investigate terrorist issues online. His sentence will be handed down on January 10.