VIENNA — Both suspects in a foiled plot to attack Taylor Swift shows in Vienna appeared to be inspired by the Islamic State group and al-Qaida, Austrian authorities said Thursday, and investigators found bomb-making materials at one of their homes. Officials said one of the two confessed to planning to “kill as many people as possible outside the concert venue.”

Three sold-out concerts were canceled Wednesday because of the plot, devastating Swifties from across the globe. Many of them had dropped thousands of euros (dollars) on travel and lodging in Austria’s expensive capital city to attend the Eras Tour shows at the Ernst Happel Stadium, which sat empty Thursday morning.

Concert organizers said they had expected up to 65,000 fans inside the stadium at each concert and as many as 30,000 onlookers outside, where authorities said the suspects planned to strike. The foiled attack was planned for Thursday or Friday, according to Austria’s interior minister, Gerhard Karner.

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Main Suspect Confessed to Planning Attack Last Month

The main suspect, 19, confessed that he had started planning the attack last month, authorities said, and just a few weeks ago uploaded to the internet an oath of allegiance to the current leader of the Islamic State group.

He was “clearly radicalized in the direction of the Islamic State and thinks it is right to kill infidels,” said Omar Haijawi-Pirchner, head of the Directorate of State Security and Intelligence.

The suspect planned to use knives or homemade explosives in the attack, Haijawi-Pirchner said.

During a raid of the suspect’s home in Ternitz, south of Vienna, investigators found chemical substances and technical devices that indicated “concrete preparatory acts,” said Franz Ruf, director general for public security at the Ministry of the Interior.

Authorities said they also found Islamic State group and al-Qaida material at the home of the second suspect, who is 17. That suspect, who has so far refused to talk, was employed a few days ago by a company providing unspecified services at the venue for the concerts. The 19-year-old is an Austrian with North Macedonian roots. The 17-year-old is an Austrian with Turkish and Croatian roots.

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Suspects Underwent Clear Social Changes Recently

The North Macedonian Interior Ministry released a statement Thursday saying that it had received a request from Austria to look into the 19-year-old.

Both teens were arrested Tuesday. Neither of their names was released in line with Austrian privacy rules.

The suspects had undergone clear social changes recently, authorities said. The 19-year-old had quit his job but said he “still had big plans,” while the other broke up with his girlfriend. Neither suspect appeared to have a ticket to any of the shows, Haijawi-Pirchner said.

Karner said that Austria’s intelligence service had worked closely together with foreign intelligence services to capture the two teens. He did not identify the services, but added that the help was needed because Austrian investigators, unlike some foreign services, can’t legally monitor text messages.

No other suspects are being sought, though a 15-year-old who had been in contact with both suspects was also interrogated by police, Karner said.

“The situation is serious. But we can also say: A tragedy was prevented,” he said.

Fans Devastated as Concerts Canceled for Safety

Concert organizer Barracuda Music said in an Instagram post late Wednesday that it had “no choice but to cancel the three scheduled shows for everyone’s safety.”

Barracuda said all tickets would be refunded. The same message was posted under the Vienna dates on Swift’s official website. Austrian rail operator OeBB in the meantime said that it would reimburse fans for unused train tickets for the concerts.

Swift has not spoken publicly about the plot or canceled shows. “Taylor Nation,” a verified Instagram page widely believed to be run by her team, reposted the announcement from Barracuda Music in a “story,” which is only visible for 24 hours. Her main account has not posted anything.

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Last month, an attacker in England killed three girls and wounded 10 people in a knife attack during a Taylor Swift-themed dance and yoga class. Swift at the time said she was ”completely in shock” over the attack.

Austrian Chancellor Karl Nehammer on Thursday defended organizers’ decision to cancel the concerts, saying it was justified because the arrests of the suspects occurred too close to the shows, scheduled for Thursday, Friday and Saturday.

“I understand very well that those who wanted to experience the concert live are very sad,” Nehammer told a news conference. “Moms and dads are looking after their daughters and sons, who were full of enthusiasm and anticipation for this concert. But it’s also important that in such serious moments as now, it’s inevitable that safety comes first.”

Swift is expected to perform at London’s Wembley stadium in five concerts between Aug. 15 and 20 to close the European leg of her record-setting Eras Tour.

London Mayor Sadiq Khan said that while he understood Vienna’s reasons for canceling, “We’re going to carry on.” Khan said the capital’s authorities were prepared for shows there following lessons learned from a 2017 attack at an Ariana Grande concert in Manchester, England, that killed 22 people.

A suicide bomber had set up a knapsack with explosives in Manchester Arena. The bomb detonated at the end of Grande’s concert as thousands of young fans were leaving.

Swift’s biggest fear has always been that such large-scale violence could take place at her concerts, the superstar told Elle magazine in 2019 ahead of her Lover Tour, which was ultimately canceled because of the coronavirus pandemic. The attack at Grande’s concert, as well as a 2017 mass shooting at an outdoor country music festival on the Las Vegas Strip where 58 people were killed, worried Swift as she prepared to circle the globe.

“I was completely terrified to go on (the Lover Tour) this time because I didn’t know how we were going to keep 3 million fans safe over seven months,” she told the magazine. “There was a tremendous amount of planning, expense, and effort put into keeping my fans safe.”

An official inquiry reported in 2023 that Britain’s domestic intelligence agency, MI5, didn’t act swiftly enough on key information and missed a significant opportunity to prevent the Manchester bombing, the deadliest extremist attack in the United Kingdom in recent years.

Terrorism expert Magnus Ranstorp, based at the Swedish Defense University in Stockholm, told The Associated Press by phone that any mass public event constitutes a potential threat now.

“So we shouldn’t be surprised that these extremely popular iconic popstars that attract a massive audience will also attract terrorists that want to create fear and destruction and mayhem,” he said.