Kelly: Well, it's something that's on our radar screen. I mean in an extreme situation, you would have some means to take down a plane.
Pelley: Do you mean to say that the NYPD has the means to take down an aircraft?
Kelly: Yes, I prefer not to get into the details but obviously this would be in a very extreme situation.
Pelley: You have the equipment and the training.
Kelly gave us an extraordinary look inside the counter-terrorism bureau, the training - like this assault team practicing for a hostage situation in a subway car - and the astounding technology that has been designed and built specifically for the NYPD.
We started with the threat that no one wants to imagine - a nuclear device smuggled into the city.
Out on the East River, we went along on an NYPD boat that was designed by one of the federal government's nuclear laboratories.
Mike Riggio: Within the boat itself we have permanently mounted and installed radiological and nuclear detectors. And the good news is that the detection equipment is very sophisticated and it is very sensitive.
Beyond the water, Kelly has radiation detectors circling the city in helicopters; in trucks down on the street. And thousands of cops have automatic nuclear detectors on their gun belts. The technology is so sensitive Inspector Mike Riggio told us they often stop pleasure boats - for a reason that we found amazing.
Riggio: We'd pull up along side the boat and we'd interview. And that lets us find out that, hey this person may have just had some type of medical procedure.
People who had medical radiation treatments, trigger the detectors.
Pelley: So you like your chances of detecting a dirty bomb or a nuclear device?
Riggio: We do. We do.
Kelly has built something else that most New Yorkers never see. It is nearly impossible now to walk a block in lower Manhattan without being on television. There are 2,000 cameras, and soon there will be 3,000 - all of which feed into this control center housed in a secret location.
Jessica Tisch: Nobody has a system like this.
Jessica Tisch helps run this $150 million surveillance system that monitors the cameras and all those radiation detectors. A powerful computer, using artificial intelligence actually watches all of the cameras at once and it knows if a package has been left in one place too long.
Tisch: The camera has identified that this is the shape and the size of a potentially suspicious unattended package. It's narrowing in on it.
Pelley: And it counted how long that bag was motionless.
Pelley: And this center will call a patrol officer and say, "Hey go check out that bag."
Look what happened last year when the cameras picked up a bag dropped outside the New York Stock Exchange. Within minutes the bomb squad moved in, they used a portable X-ray to look inside and then the bomb tech crawled up to open it.
Tisch: And thank God, it's someone who dropped their lunch.
Pelley: Somebody's lunch.
It's not just lunch bags and suspicious packages that catch the computer's eyes. Tisch showed us how the system can search for a suspicious person - based on a description. A red shirt for example.