The trial of a man accused of pledging allegiance to ISIS and plotting to attack one of superstar singer Taylor Swift's concerts in Vienna nearly two years ago has begun in Austria.

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 in her record-setting Eras Tour were devastated, but rallied to turn Vienna into a citywide trading post for friendship bracelets and singalongs.

The defendant, a 21-year-old Austrian citizen known only as Beran A., in line with Austrian privacy rules, faces charges including terrorist offenses and membership in a terrorist organization. He could be sentenced to up to 20 years in prison.

He is being tried 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 ISIS. Beran A. and Arda K. never carried out their attacks.

Beran A.'s defense attorney, Anna Mair, told The Associated Press on Monday that her client plans to plead guilty to most of the charges but did not specify which ones. Only Beran A. is charged in connection with the Taylor Swift plot.

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 U.S. provided intelligence that led to the arrests.

"They were plotting to kill a huge number — tens of thousands of people at this concert, including, I am sure, many Americans — and were quite advanced in this," CIA Deputy Director David Cohen said a few weeks after the arrests. "The Austrians were able to make those arrests because the agency and our partners in the intelligence community provided them (with) information about what this ISIS-connected group was planning to do."

Beran A. also allegedly networked with other ISIS members 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.

Swift learned of the bomb plot while on a plane flying to Austria, according to her Eras Tour documentary.

"Having our Vienna shows cancelled 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 May 12.

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.

Beran A. and Arda K. did not carry out their alleged plans in Turkey and the UAE. Beran A. returned to Vienna and then allegedly began plotting to attack a Swift concert there.

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.

The nearly 150-show Eras Tour, which began in March 2023 and ended in December 2024, covered five continents and sold more than 10 million tickets – making it the first tour in history to surpass $1billion in ticket sales.