NEW YORK (AP) — The FBI said Tuesday that it found explosive residue in a Pennsylvania storage unit as part of an investigation into two men charged with bringing homemade bombs to a protest outside the home of New York City’s mayor.

Emir Balat, 18, and Ibrahim Kayumi, 19, told police after their arrests that they were inspired by the Islamic State group, according to law enforcement officials and a criminal complaint.

The men live in the Philadelphia suburbs and drove together to New York City on Saturday to carry out the attack near Gracie Mansion in Manhattan, officials said.

In response to police questioning, Balat said he hoped to accomplish something “even bigger” than the Boston Marathon bombing, which killed three people, the complaint said.

Overnight Monday, FBI bomb technicians conducted controlled detonations of the explosive residue found at a public storage facility in Langhorne, Pennsylvania, near where Balat’s family lives, the agency said.

The explosion resulted in “several loud bangs,” the Middletown Township Police Department said Tuesday, adding that there was no threat to residents. The FBI said it has conducted multiple searches in connection with the investigation.

White House press secretary Karoline Leavitt on Tuesday called the attack “absolutely despicable” and said government investigators and prosecutors won’t rest until the perpetrators are brought to justice.

Much remains unknown about the motives, planning and relationship between Balat and Kayumi.

Court documents show Emir Balat’s father, Selahattin Balat, is a native of Turkey who was granted asylum in the United States in 1998 and later became a U.S. citizen. In a 2009 bankruptcy filing, he listed his occupation as painter and said he had three children.

Emir Balat is a senior at Neshaminy High School in Langhorne. A school spokesperson said he enrolled in a virtual program in September and had not attended in-person classes since.

His lawyer, Mehdi Essmidi, said his client had “complicated stuff going on” in his personal life, without elaborating. Essmidi said he did not believe the two young men had known each other for long.

Kayumi is from Newtown, about 4 miles (6.5 kilometers) north of Langhorne. He graduated in 2024 from Council Rock High School North, according to a school spokesperson.

His attorney did not speak to reporters following a court hearing Monday and declined to comment when reached by The Associated Press.

Online records show that Kayumi’s parents have owned and worked at multiple Popeyes fast food locations, including in Philadelphia, Brooklyn and Atlantic City.

His mother filed a missing person report with police Saturday, the day of the protest, saying her son had not been seen since that morning, according to the complaint.

Prosecutors, police and FBI officials say Balat and Kayumi joined a throng of counterprotesters at a small, anti-Muslim rally organized by far-right activist Jake Lang. A Christian nationalist, Lang is a critic of New York Mayor Zohran Mamdani, a Democrat and the first Muslim to hold the office.

Journalists photographed Balat hurling a device, smoking with a lit fuse, that was later found to contain the explosive TATP. The object, which also contained nuts and bolts, extinguished itself without harming anyone.

Balat then dropped a second object near some police officers and tried to run, but was tackled and arrested, according to a court complaint.

Balat and Kayumi were being held without bail after their court appearance on charges that include attempting to provide material support to a foreign terrorist organization and using a weapon of mass destruction. They were not required to enter a plea.

New York Police Commissioner Jessica Tisch said Monday there were no indications that the attack was connected to the ongoing war in Iran, but said the city remained on a heightened state of alert.

On Tuesday afternoon, a park near the mayor’s residence was evacuated and several surrounding streets were closed as police investigated reports of a “suspicious device.”

The object was later determined to be nonthreatening.

Mamdani was not home at the time and Gracie Mansion was not evacuated, a City Hall spokesperson said.

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Associated Press reporter Anthony Izaguirre contributed to this report.