Classic story and hat tip to WoTR. It is within a wider article on immigrants and national security.

The FBI, too, has benefitted from the service of immigrants. A particularly striking example in the national security realm is that of Dimitry Droujinsky, the son of Russian immigrants to Palestine who later came to the United States. Droujinsky had a multi-decade career in the FBI; his specialty was impersonating KGB officers to ensnare Americans who had spied for Moscow. His career reached all the way into the late 1990s when he came back from retirement to help bring to justice David Sheldon Boone, a former National Security Agency official who had sold sensitive documents to Moscow in the last days of the Cold War. Boone had Russian-language training and might not have been fooled by an FBI agent who had learned his Russian in a classroom.
Link:https://warontherocks.com/2018/02/th...us-hard-power/