Andrew Arrabaca doused a stairwell with gasoline, ignited it with a firework and sent flames and smoke up the facade of the building before he fired five to seven pellets from an airsoft gun, the FBI said.
Arrabaca, 43, is a former U.S. Army soldier from 2001-2005, who worked as a mechanic on Patriot missile systems.
"Mr. Arrabaca came armed, with bad intentions," FBI Assistant Director in Charge James Barnacle said.
The Poughkeepsie resident had two axes, a hammer, a machete, and knives in addition to fireworks and gasoline, officials said.
3 hurt after man sets off device outside NYC federal building
The flames quickly spread but they were put out before they reached the building where immigrants are processed and FBI and ICE officers are located.
The suspect -- described by the Department of Homeland Security as an "anti-ICE rioter" -- was tackled by a Federal Protective Service police officer, DHS said. He was taken into custody.
"26 Federal Plaza has long been a target of extremist acts of terror. Today, the extremist was brought here," Barnacle said.
Several people suffered minor injuries, including one civilian and two government employees.
"He did say he was targeting the building and did say he was OK with" people getting hurt whether they were federal employees or civilians, Barnacle said.
The NYPD said it was "looking at the cart the suspect wheeled with him" which had a sign reading "ICE Off Our Streets."
Officials say that leading up to the incident, Arrabaca took a subway train from Harlem down to the Penn Station area, then walked down and stayed overnight in the vicinity of the Holland Tunnel, on the street. They say he went to the area near 26 Federal Plaza around 5 a.m., then ventured to the spot where he started the fire around 8 a.m.
Official charges in the incident have yet to be filed.
New York City Mayor Zohran Mamdani called the incident "deeply disturbing."
"I'm relieved no one was seriously injured and that a suspect is in custody," Mamdani said. "My team is in touch with the NYPD and we will support the federal investigation. Our administration will continue to ensure that every New Yorker is safe in their city - and hold accountable any who threaten that."
The FBI New York Joint Terrorism Task Force is investigating the incident.
(ABC News contributed to this report.)
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