A Welsh teenager has been found guilty of plotting a terror attack on the day of a Justin Bieber concert in Cardiff

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A Welsh teenager has been found guilty of plotting a terror attack on the day of a Justin Bieber concert in Cardiff.

The 17-year-old of British heritage from Rhondda Cynon Taff, who cannot be named due to his age, was detained by police on June 30, the same day as the singer’s gig at the city’s Principality Stadium, formerly known as the Millennium Stadium.

Birmingham crown court heard that the teen searched online for details about the event’s security procedures and had a copy of the concert poster saved to his computer. Police also found a claw hammer, kitchen knife and “martyrdom letter” in the boy’s school rucksack upon searching his home. The note saw the teen declare himself as “a soldier of the Islamic State.”

The teen had denied preparing to commit acts of terrorism and four other terrorism charges, telling the court that he didn’t believe in Islam but instead had a “stupid interest in the gory” and was curious about ISIS. He said that he “never thought about actually” carrying out an attack.

“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. “I wanted to see if it was possible, not for me but from someone else’s point of view.”

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However, Sue Hemming, from the Crown Prosecution Service, said: “This teenager’s behavior over many months leaves no doubt that he intended to kill and maim as many people as possible in an attack reminiscent of the incident on Westminster Bridge. The CPS presented overwhelming evidence that he was prepared to die for [an] extremist worldview and he will now rightly face the prospect of a substantial prison sentence.”

Judge Mark Wall QC said: “The offenses for which he has been convicted obviously merit a significant custodial sentence. One of the things I will have to consider is whether there ought to be an indefinite sentence. I need as much information on him as you wish to place before me.”

Since being charged, the boy had been diagnosed with autistic spectrum disorder, although the court heard that this wouldn’t have affected his ability to make decisions.

The teen will remain in custody until a sentencing hearing on Jan. 10, 2018.

This article originally appeared on Nme.com