While the nation spent Thursday wondering if the Parkland, Fla. school district might have missed signs that Nikolas Cruz was destined to kill 17 people at Marjory Stoneman Douglas High School on Valentine’s Day, another school district over 1,ooo miles north became heroes when students at a school in Harlem set off a chain reaction that would ultimately foil what is being described as a possible terror attack targeting New York City.

Mayor Bill de Blasio, who joined the Police Commissioner of the City of New York and members of both the FBI and the U.S. Attorney’s Office Thursday night at a press conference, said a bomb threat made against the school by a student and subsequent tips from staffers led to the arrest of 28-year-old twin brothers Christian and Tyler Toro.

“This is a moment to remind all New Yorkers, to remind everyone, that the idea that if you see something, you say something is more pertinent than ever,” de Blasio said. “We get daily reminders of the threats arrayed against us.”

De Blasio also called the arrests “another example of the very close working relationship between the NYPD and the FBI; the City of New York and our federal partners.”

Christian, who had been a teacher at the school, resigned from his position about a month after a student called in a bomb threat in early December and an investigation began. The Toros had apparently been paying two students from the school to help them dismantle fireworks, the contents of which were collected and stored by the brothers. That started in October 2016; by December, the bomb threat was called in; in January, Christian Toro resigned.

Following his resignation, his brother Tyler was asked by the school to return a laptop they had issued his brother. When he did and it was examined, bomb making instructions were found to have been downloaded, leading authorities to conduct a search of the brothers’ apartment.

What they found was enough for the FBI to swear out a complaint and charge the brothers each with one count of unlawfully manufacturing a destructive device, which carries a maximum of 10 years in prison. The brothers also had a diary and disturbing phrases jotted on index cards, leading de Blasio to declare that “many, many lives” were likely saved.

Law enforcement obtained a search warrant and raided the Toros’ Bronx apartment on Thursday and found “over 30 pounds of chemicals, which taken together in certain combinations, constituted explosive precursor materials,” officials said.

A handwritten diary with Tyler Toro’s name on it was recovered. Officials said it included notations about an operation “flash.”

The diary, according to the complaint, stated, among other things: “Christian arrested” and “If you’re registered as a sex offender, things will be difficult.” [Christian Toro was reportedly arrested in late January for raping a minor.]

“We are twin Toros strike us now, we will return with nano thermite” and “I am here 100 percent, living, buy weapons. Whatever we need,” the diary read, according to the complaint.

The diary added, “I hope this doesn’t turn into a scene from Goodfellas,” after threatening retribution if anyone were to “strike us now.”

A backpack belonging to Christian Toro was also allegedly recovered, containing a purple index card with a handwritten note, which read: “Under the full moon the small ones will know terror.”

Let that be a reminder to all New Yorkers: if you have information you find unsettling, come forward to law enforcement. You'll never know when that might be the moment you save a life.

— Mayor Bill de Blasio (@NYCMayor) February 16, 2018

Mayor de Blasio and police detectives credited the school and the community for coming forward with what they knew to stop what could have been a tragedy.

“We get daily reminders of the threats arrayed against us, but what we’re seeing here in this case already is, some good people stepped forward with information,” de Blasio said.

The full press conference can be found below.