It was Sunday night, a day after a bombing hit Manhattan last year, and investigators did not know who was in the car that had left the suspect’s home in New Jersey and was headed east on the Belt Parkway in Brooklyn. And they did not know where the car was going.

Intercepting it before its destination — perhaps a safe house — risked robbing the F.B.I. of a crucial lead. Hanging back risked letting the car get into the maze of Kennedy Airport and then get away or, far worse, letting the occupants launch an attack.

In a command post not far from the bombing site in Chelsea, with radio traffic crackling and an F.B.I. agent narrating the pursuit, chiefs from an array of law enforcement agencies weighed their options. The final call belonged to an F.B.I. special agent in charge of the counterterrorism division in New York who had forged his career in turf battles overseas and emerged as an ambassador within government for the F.B.I. way.

The agent, Carlos T. Fernandez, ordered the car stopped. Five people, some of them relatives of the bombing suspect, were in the car and were questioned. The suspect was arrested the next day.