Noah Schachtman passes along a TV news report that was taken down without explanation:
“In the end, it was secret Army intelligence planes that did him in. Armed with his cell phone number, they circled the skies over the New York area, intercepting a call to Emirates Airlines reservations, before scrambling to catch him at John F. Kennedy International Airport.”
He then geeks out over the technology, but I call bullshit on the whole story. If the FBI had Shahzad's cell phone number, all they needed to do to listen to his phone calls was wiretap his line. It would be quick, given the state of the evidence it would be easy to get a warrant, and unlike a spy plane over a particular location, it would catch his conversations no matter where in the world he was.