He was observed walking slowly, reviewing his surroundings and looking into cars and the reflection of store windows. He took circuitous routes to meetings, changing his clothes beforehand, employing an approach that bore hallmarks of “intelligence tradecraft,” an FBI agent wrote in 2018.

On Wednesday, the subject of the FBI’s surveillance, Ahmadreza Doostdar, was sentenced to more than three years in prison for serving as an illegal agent of Iran, concluding a prosecution in Washington that addressed the global tensions between the U.S. and Iran.