WIENER NEUSTADT, Austria (AP) — A man accused of pledging allegiance to the Islamic State group and plotting to attack one of superstar singer Taylor Swift’s concerts in Vienna nearly two years ago pleaded guilty as his trial began on Tuesday, his lawyer said.

The plot was thwarted, but Austrian authorities still canceled Swift’s three performances in August 2024.

The singer’s fans, known as Swifties, who had flown to Austria from across the globe to attend a performance of her record-setting Eras Tour were devastated, but rallied to turn Vienna into a citywide trading post for friendship bracelets and sing-alongs.

The defendant, a 21-year-old Austrian citizen known only as Beran A., in line with Austrian privacy rules, faced charges including terrorist offenses and membership in a terrorist organization.

He could be sentenced to up to 20 years in prison, and has been in custody since August 2024.

The Vienna plot drew comparisons to a 2017 attack by a suicide bomber at an Ariana Grande concert in Manchester, England, that killed 22 people.

The bomb detonated at the end of Grande’s concert as thousands of young fans were leaving, becoming the deadliest extremist attack in the United Kingdom in recent years.

Defendant regrets his actions

Anna Mair, his defense attorney, said her client pleaded guilty to the charges related to the concert plot.

“Of course, he deeply regrets it all,” Mair said outside the court, adding that “he says it was the biggest mistake of his life.”

Austrian media reported that he also pleaded guilty to being a member of a terrorist organization.

Beran A. is facing trial alongside Arda K., whose full name also has not been made public.

They, along with a third man, planned to carry out simultaneous attacks in Saudi Arabia, Turkey and the United Arab Emirates during Ramadan in 2024 in the name of the Islamic State group.

Beran A. and Arda K. never carried out their attacks.

Only Beran A. was charged in connection with the concert plot. He pleaded not guilty to the charges related to the plot for simultaneous attacks.

He allegedly planned to target onlookers gathered outside Ernst Happel Stadium — up to 30,000 each night, with another 65,000 inside the venue — with knives or homemade explosives.

The suspect hoped to “kill as many people as possible,” authorities said in 2024. The US provided intelligence that fed into the decision to cancel the concerts.

Beran A. also allegedly networked with other members of the Islamic State group ahead of the planned attack.

Prosecutors say they discussed purchasing weapons and making bombs, and that the defendant also sought to illegally buy weapons in the days ahead of the performance.

In addition, he swore allegiance to the militant group.

Authorities searched his apartment on Aug. 7, 2024, and found bomb-making materials. The concerts were scheduled to begin the next day.

“Having our Vienna shows canceled was devastating,” Swift wrote in a statement posted to Instagram two weeks later.

“The reason for the cancellations filled me with a new sense of fear, and a tremendous amount of guilt because so many people had planned on coming to those shows.”

The trial is being held in Wiener Neustadt, about an hour south of Vienna. The proceedings are set to continue on May 12.

Three attacks planned in Saudi Arabia, Turkey and UAE

Prosecutors have also filed terrorism-related charges against Arda K. in the trial in connection with the plan for simultaneous attacks in Saudi Arabia, Turkey and the United Arab Emirates.

The third man in that plot, Hasan E., allegedly stabbed a security guard with a knife at the Grand Mosque in Mecca, Saudi Arabia, on March 11, 2024.

He was arrested and remains in pretrial detention in Saudi Arabia, Austrian prosecutors said.