At least one arrest was made when law enforcement executed a search warrant at Willow Avenue and Clinton Street.
Authorities arrested Alexander Heifler, 26, Thursday night on charges of unlawfully possessing and unlawfully making firearms and accused him of plotting to "go after" the activist, Nerdeen Kiswani, co-founder of Within Our Lifetime, an organizer of many of the pro-Palestinian protests in New York City.
"Heifler did not apply to, nor receive approval from, the secretary of the treasury to make the firearms," the criminal complaint said.
Kiswani is not identified by name in the criminal complaint but she posted on social media the FBI informed her she was the alleged target.
In the statement she vowed she would not stop speaking up for the people of Palestine.
An NYPD undercover officer broke the case open after the department identified Heifler online, infiltrated a group chat, developed a relationship and thwarted the plot.
On February 10, the complaint says on a video call with undercover NYPD officers, Heifler said he was "looking for space where he could throw Molotovs."
The next day, it says Heifler met with them in person to discuss "vandalizing the home of a certain individual," that individual being Kiswani.
On March 4, prosecutors say Heifler told the undercover officers he had Kiswani's address, and they drove there to conduct surveillance.
On March 23, they say Heifler sent a text message saying "Thursday night would be best to bake."
The next day, the officers agreed to meet at Heifler's residence in Hoboken.
Then on Thursday, the undercover officer personally witnessed Heifler making the eight Molotov cocktails in Hoboken, which led to his arrest, officials say.
An eyewitness described what the saw.
"We looked out the window of the bedroom window right there, and it was a bunch of these FBI guys with FBI, tags on the back, and they were knocking on the door," said witness James McDonald. "Knocking on the door. All of a sudden we see four or five guys come out in handcuffs."
The criminal complaint also revealed information about Heifler's plan once the attack was carried out.
"Heifler also told the (undercover officer) that he had an address where they could hide out after they threw the Molotov cocktails" and discussed a plan to leave the country, the complaint said.
Authorities allege the plan was to throw the Molotov cocktails at Kiswani that night.
New York Police Commissioner Jessica Tisch lauded the undercover officer who discovered and disrupted Alexander Heifler's alleged plan.
"This NYPD investigation uncovered an alleged plot by Alexander Heifler to carry out a violent attack against Nerdeen Kiswani. Our undercover officer identified and tracked the threat - first online and then in person - allowing us to disrupt the planned attack, take Heifler into custody, and ensure that no one was harmed. This is exactly how our intelligence and counterterrorism operation is designed to work - a sophisticated apparatus built to detect danger early and prevent violence before it reaches our streets. Once again, the men and women of the NYPD have done the courageous and dangerous work necessary to keep people safe," Tisch said in a statement.
Law enforcement believes they stopped an imminent threat and the FBI said there is no threat to public safety.
Mayor Zohran Mamdani released a statement calling the alleged assassination attempt "a chilling act of political violence."
"Let me be clear: We will not tolerate violent extremism in our city. No one should face violence for their political beliefs or their advocacy. I am relieved that Nerdeen is safe," Mamdani said.
He later said in a statement that the suspect was "A member of an offshoot of the Jewish Defense League -designatedby the FBI as a 'known violent extremist organization.'"
Kiswani then responded to Mamdani's statement on X, saying "Thank you for this important statement. There has never been an NYC Mayor willing to call out Jewish extremism for what it is. I also appreciate that you clarified the JDL member planned to flee to Israel. This is an important detail that confirms what I have been thinking."
Hoboken Mayor Emily B. Jabbour released a statement Friday and said there was "no danger to residents and no ongoing threat."
Heifler remains in federal custody after appearing before a magistrate judge in Newark on Friday afternoon. He is being held following the brief hearing, where his public defender reserved the right to seek bail at a later date.
(ABC News contributed to this report.)
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