NYPD officials say the detectives will help deal with the dozens of reports that are pouring in, which are currently 200% the volume of a normal week. Some are called into the toll-free number 888-NYC-SAFE, some come in to 911, and others are flagged by keyword searches on social media and Internet forums. Just this week, the New York State Police launched a new smartphone app called "See Something, Send Something" that allows people to send in photos of suspicious activity that will be investigated by the appropriate authority, including the NYPD.
The NYPD unit tracks each and every one, 24 hours a day, seven days a week.
The tips "could be or could not be crimes," Thomas Galati, NYPD assistant chief for counterterrorism and intelligence, told CNN. He adds that they range widely, from men seen abandoning a car on the Brooklyn Bridge to someone posting a video showing guns with the hashtag for September's papal visit.
"To some extent, a lot of the investigations end up without arrests because it doesn't turn out to be criminality," he said.
Police around the country spend a lot of resources chasing threat reports, discarding many not viewed as worth the time. But because of New York's status as a top terror target, the NYPD believes it can't let even the smallest tips go unfollowed.
"It's important to New York City that we have this" capability, Galati said. "The level of threat we have is different."
The FBI says it works with the NYPD to evaluate all threat reports as part of the Joint Terrorism Task Force.
"All leads are addressed until threats are properly mitigated," said Carlos Fernandez, the FBI's special agent in charge of counterterrorism division in New York. "There is oversight from FBI Headquarters and we work collaboratively with all our partners to ensure transparency and inclusiveness. We recognize that success is a team effort, and are enormously grateful for the joint commitment by all agencies on the JTTF to keep us safe from harm."
Massive security effort for Francis visit
To illustrate how the Leads unit does its work, Galati and top officials overseeing the unit described another recent similar period of intense security during which the NYPD and the FBI were overwhelmed with threat reports.
The visit of Pope Francis in September, which coincided with the United Nations General Assembly, prompted the biggest security operation in the city's history, NYPD officials said.
The throngs of religious pilgrims who turned out for the visit faced possible threats from ISIS, al Qaeda and even domestic terrorists, all monitored by the U.S. Secret Service, FBI and the NYPD.
The Leads unit has investigated more than 500 cases since the start of 2015.
One such threat report occurred in the week before the Pope was due to arrive in New York, illustrating the type of concern that keeps dozens of NYPD investigators busy.
It began with an unexpected package that provoked immediate alarm when it was opened: $1,200 worth of equipment to make bullets and multiple high-capacity magazines for various caliber guns.
The homeowners who received the package were set to rent their eighth-floor apartment via Airbnb to a visitor from Argentina. The apartment's location, in the bustling Herald Square neighborhood, is a prime location for a family planning to arrive in the coming days to spend a week's holiday in New York.
But the location also was along a route the Pope, a native of Argentina, could take on his way to saying mass at Madison Square Garden, a block away.
The NYPD Leads unit jumped into action, coordinating with more than a dozen agents and officers from the FBI, Secret Service, Port Authority Police, Customs and Border Protection and the State Department.
The package was sent from a manufacturer in Scottsdale, Arizona. It was ordered by the renter of the Airbnb apartment in Herald Square, Diego Florio, who was planning to arrive from Buenos Aires days before Pope Francis. He had asked the Airbnb host to allow a package to be delivered and held for him until his arrival. The apartment owner had mistakenly opened the package.
Investigators compiled a dossier on Florio and his wife and daughter, including visa and travel records, social media history and arrest records provided by Argentine police.
By the time of Florio's flight to New York, two days before Pope Francis was due to arrive, investigators were beginning to feel that Florio was simply at the center of an unhappy series of coincidences.
The high-capacity magazines are illegal in New York City, and he could be arrested if he possessed them, investigators determined. And what if Florio has other accomplices the investigators haven't found out about, and that he's part of a broader plot?
"It all appears to be innocent in nature, but nobody knows this at the time," says William Viscardi, deputy inspector for the criminal intelligence section.
Officials decided to let Florio fly into the country so they could interview him.
As many as 18 investigators, from a dozen agencies, met Florio's flight at John F. Kennedy International Airport. The NYPD, FBI and Secret Service interviewed him.
Florio was licensed in Argentina to have guns, and it appeared likely that his purchases were simply a way to buy items cheaper in the U.S. than they would be in his home country.
Investigators believed Florio's story. But, with the Pope due in New York City in a few hours they decided they couldn't allow him into the country.
"They were put on the next flight home," said NYPD Lt. Marc Moreno. "They were just coming here as tourists. His timing -- of everything he was doing -- was his biggest enemy. You can't too many chances with these things."
Reached on the phone in Argentina, weeks later Florio expressed exasperation at the events.
"It was a disaster, " he said before deciding he didn't want to answer any more questions about his ill-fated trip to New York.
The Pope visited New York without incident. The Leads unit chased multiple other reports, including a group of men who tried to prank an Uber driver into thinking their cargo of duffel bags carried explosives. After hours of investigating, including a bomb squad search of a storage facility where the duffel bags were stored, NYPD determined the men were using the bags to store personal belongings while moving apartments.
And then there was the man in Yonkers, 15 miles north of New York City, who posted a video on Snapchat showing him loading a rifle and putting it into a bag. He appended one of the popular social-media hashtags used for the Pope Francis visit. He told NYPD detectives he used the hashtag as a way to get more people to see his video. The gun was seized because he had altered it, making it illegal.