Trey was drifting around the campus, dressed like a student, lugging his backpack, scoping out places for his bombs.

The library closed at midnight. The four team members, as well as Ahmed in his basement in Buffalo, were in radio contact. Denny, the leader, announced at 12:15 that all was proceeding as planned. At 12:20, Trey, dressed like a student and hauling a bulky backpack, entered the McCarren Residential College in the heart of the campus. He saw the same surveillance cameras he had seen the previous week. He took the unwatched stairs to the second floor, ducked into a coed restroom, and locked himself in a stall. At 12:40, he reached into his backpack and removed a tin can about the size of a twenty-ounce bottle of soda. He set a delayed starter and hid it behind the toilet. He left the restroom, went to the third floor, and set another bomb in an empty shower stall. At 12:45, he found a semi-dark hallway on the second floor of a dormitory and nonchalantly tossed a string of ten jumbo Black Cat firecrackers down the hall. As he scrambled down the stairwell, the explosions boomed through the air. Seconds later, both smoke bombs erupted, sending thick clouds of rancid fog into the hallways. As Trey left the building he heard the first wave of panicked voices. He stepped behind some shrubs near the dorm, pulled a disposable phone out of his pocket, called Princeton’s 911 service, and delivered the horrifying news: “There’s a guy with a gun on the second floor of McCarren. He’s firing shots.”

Smoke was drifting from a second-floor window. Jerry, sitting in the dark study carrel in the library, made a similar call from his prepaid cell phone. Soon, calls were pouring in as panic gripped the campus.

Every American college has elaborate plans to handle a situation involving an “active gunman,” but no one wants to implement them. It took a few dumbstruck seconds for the officer in charge to push the right buttons, but when she did, sirens began wailing. Every Princeton student, professor, administrator, and employee received a text and e-mail alert. All doors were to be closed and locked. All buildings were to be secured.

Jerry made another call to 911 and reported that two students had been shot. Smoke boiled out of McCarren Hall. Trey dropped three more smoke bombs into trash cans. A few students ran through the smoke as they went from building to building, not sure where exactly the safe places were. Campus security and the City of Princeton police raced onto the scene, followed closely by half a dozen fire trucks. Then ambulances. The first of many patrol cars from the New Jersey State Police arrived.

Trey left his backpack at the door of an office building, then called 911 to report how suspicious it looked. The timer on the last smoke bomb inside the backpack was set to go off in ten minutes, just as the demolition experts would be staring at it from a distance.