Federal investigators set off homemade improvised explosive devices (IEDs) in a "controlled detonation" at a Pennsylvania storage facility overnight Monday (March 9), deepening a terror investigation tied to an alleged ISIS-inspired bomb attack near New York City's mayoral residence over the weekend.

According to Fox News, the FBI executed a search warrant at a Public Storage location on South Flowers Mill Road in Langhorne, Pennsylvania, as part of its investigation into two suburban Pennsylvania teenagers accused of throwing IEDs outside Gracie Mansion, the official residence of New York City Mayor Zohran Mamdani, on Saturday (March 7).

The two suspects, Emir Balat, 18, and Ibrahim Kayumi, 19, face serious federal charges, including attempting to provide material support to a designated foreign terrorist organization and use of a weapon of mass destruction. Both were ordered held without bail following a court appearance Monday (March 9).

The alleged attack unfolded during a far-right, anti-Islam protest organized by activist Jake Lang outside Gracie Mansion. Balat allegedly hurled a jar-sized device packed with the explosive TATP, a chemical commonly used in homemade bombs worldwide, into the crowd. The device extinguished itself just steps from police officers. Balat then retrieved a second device from Kayumi, dropped it near officers, and attempted to flee before police tackled and arrested him. Kayumi was arrested shortly after.

A search of the suspects' vehicle, registered to one of Balat's relatives and found a few blocks from the arrest scene on Sunday, turned up a fuse, a metal can, and a list of chemical ingredients used to build explosives.

New York City Police Commissioner Jessica Tisch made clear the devices were no minor threat. "These were not hoax devices nor smoke bombs," Tisch told reporters. "They were improvised explosive devices that could have caused serious injury or death."

Federal prosecutors say the alleged plot was far more ambitious than what unfolded on the street. According to court documents, when officers asked Balat if he was aiming for something like the 2013 Boston Marathon bombing, which killed three people and wounded hundreds, he replied, "No, even bigger." Balat also allegedly wrote on a piece of paper that he had "pledged allegiance to the Islamic State," while Kayumi told authorities he watched ISIS material on his phone and considered himself "affiliated" with the group.

James Barnacle, who heads the FBI's New York office, said the suspects "sought to incite fear and mass suffering through this alleged attempted terror attack in the backyard of an elected city official."

U.S. Attorney Jay Clayton for the Southern District of New York echoed that message at a Monday press conference. "Violence, particularly violence that has a terrorist bent, violence that is meant to chill free speech, violence that is meant to prevent us from gathering peaceably, will be met with swift justice," Clayton said.

Both suspects attended Pennsylvania high schools. Balat is a senior at Neshaminy High School in Langhorne but has not attended in-person classes since enrolling in the district's virtual program in September 2025. Neshaminy School District Superintendent Jason Bowman confirmed in a statement that there is "no information indicating any security concerns at the high school or at any of our district schools related to this situation." Kayumi is a 2024 graduate of Council Rock North High School in Newtown.

Balat's attorney, Mehdi Essmidi, said outside court that his client has "complicated stuff going on" in his personal life. "I believe he's 18 and he doesn't have any idea what he's doing," Essmidi said. He also said he does not believe the two men knew each other well before the incident.

Mayor Mamdani condemned the violence while defending the right to free speech. "Ours is a free society where the right to peaceful protest is sacred," he said. "New York City will never tolerate violence."

City officials say there is no evidence linking Saturday's attack to the ongoing war in Iran, though Tisch noted the city remains on "a heightened state of alert" in connection with that conflict.

Balat and Kayumi face five federal counts. No trial date has been set.