The New York commuters trudged along beneath Times Square: Monday morning, off to work. Walking among them was a man in a hooded sweatshirt.

Then a deafening boom came from him, and then smoke. And then the commuters ran.

The explosion, which the police said was from a pipe bomb strapped to the man, in the long corridor connecting the subway stations at Times Square and the Port Authority Bus Terminal, reverberated through the maze of tunnels and passageways of the city’s busiest transit hub. People scurried like mice, in any direction, unable to figure out where the boom came from. Some stood paralyzed.