The FBI says a search of a storage unit believed to be tied to the attempted terror attack at Gracie Mansion turned up positive for explosive residue.

Feds searched the public storage unit, near the home of Emir Balat in a Pennsylvania suburb overnight on Monday.

"FBI Special Agent Bomb Technicians and the local bomb squads conducted a controlled detonation to ensure the safety of law enforcement and others in the area," the FBI said in an update.

Local police in the area says loud explosions were heard in the area overnight, but there was no threat to the public.

Balat, 18, and Ibrahim Kayumi, 19, face five federal terrorism charges for allegedly throwing homemade IED-style explosives into a crowd during a counter-protest on Saturday outside Gracie Mansion, the home of Mayor Zohran Mamdani. The attack is being investigated as being inspired by ISIS.

"The bomb squad will respond, they will render them safe, and then they will be studied to see how they were put together, this gives us a handle on where they got the components to make these bombs, and further investigation can be led to perhaps other individuals being involved and the compiling of these components to make these bombs," said Phil Grimaldi, a retired NYPD detective.

Prosecutors allege the two crossed state lines with at least three of these explosives in tow, ready to cause catastrophic destruction and carry out an attack bigger than the Boston Marathon bombing, according to court documents.

"The video shows these terrorists, I am going to call them terrorist because that's what they were, definitely had homicide in their mind," Grimaldi said.

Photos captured Balat and Kayumi passing the makeshift explosive before video shows Balat tossing at least one over the head of a protestor before running off. He was later tackled and arrested.

Mamdani and his wife were at a museum in Brooklyn at the time of the protests and chaos. The mayor condemned the attack, calling it a heinous act of terrorism.

"Often times when we see these kinds of displays, they are not coming from New Yorkers, the protest we are speaking about, we are talking about people who come from out of state with a vision of a city that does not match up to the one that we love and live in," the mayor said on Tuesday at an unrelated press conference.

It's unclear how exactly Balat and Kayumi know each other. Balat's attorney spoke outside of court on Monday, saying his client is a high school student and requested protective custody.

They are being held without bail and are due back in court on April 8.