A 17-year-old boy has been found guilty of plotting an Isis-inspired terror attack in Cardiff, Wales, on the same day as a Justin Bieber concert.

The boy, who cannot be named due to his age, was found guilty of five terror-related charges at Birmingham Crown Court, following his arrest on June 30 — a month after a bombing at Manchester Arena killed 23 people and injured over 500 during an Ariana Grande concert, The Guardian reports. He was arrested after researching security around a Bieber concert at Cardiff’s Principality stadium and wrote a “martyrdom letter,” suggesting he had been inspired by Isis. The boy is of white British heritage.

When police raided the boy’s house, they found a claw hammer and a gutting knife in his school backpack, as well as a suicide note that read, “I am a soldier of the Islamic State. I have attacked Cardiff today because your government keep on bombing targets in Syria and Iraq. There will be more attacks in the future.”

Prosecutors told the jury that the boy had also written a note with bullet points such as “run down the non-believers with a car” and “strike the infidels who oppose Allah in the neck,” The Guardian reports. As well, the boy had set up an Instagram account promoting jihad and supporting al-Qaeda with the password “TruckAttack,” including a post that read, “May Allah bring terrorism to Cardiff on 30th June,” the BBC reports.

According to The Guardian, the boy also had web searches for “17-year-old jihad” and “vehicle mounting pavement – car ploughs through a crowd,” as well as various possible targets in the city. Among those targets may have been the Principality stadium, searching for information about Bieber concert scheduled there for June 30, including the search term “Justin Bieber security.” He also searched for the phrases “how to steal a car” and “how to steal a car from a non-believer” and visited a website detailing how to kill someone with a knife.

The defendant denied plans to carry out a terror attack and, instead, his barrister argued he had a “stupid interest in the gory,” according to the BBC. The boy told the jury he did not own a Qur’an and was merely curious in how easy it was to research terrorist topics online.

“I wanted to see how easy it was for people who had an interest in terrorism to go online and get information because the police and the government are trying to crack down on terrorism and radicalization,” he said from the stand, The Guardian reports. “I wanted to see if it was possible, not for me but from someone else’s point of view.”

The boy was found guilty of one charge of engaging in the preparation of a terrorist act, two charges of encouraging terrorism and two charges of possessing terrorist information. Sentencing will take place Jan. 10.

This article originally appeared on Billboard.