My parents always used to say the the best movie about Nazi spies in the US was The House on 92nd Street. But I was never able to watch it until a few weeks ago. It's interesting for a couple of reasons. It was produced by Louis de Rochmont, who produced the March of Time (and it certainly has that feel to it). He utilized incredible access to the FBI in DC and Quantico- there's actual footage of the real places in the movie. The FBI lent the production one of their surveillance trucks, and it makes use of their then new invention, two-way mirrors. To give the film a documentary-like feel, Rochemont uses real surveillance footage of the German Embassy from the late 1930s, and much of it was shot on location in NY (I always wondered what the Grand Central Palace, the predecessor of the Pan Am Building, looked like, and now I know). German American college grad William Dietrich (William Eythe, pinch-hitting for Tyrone Power at 20th Century Fox during World War II) is recruited by German Intelligence as an agent, but goes to the FBI and becomes a double agent. He studies at spy school in Hamburg, and comes to New York as an operative. He works under Elsa Gebhardt (Swedish actress Signe Hasso), who lives in a house on 92nd Street (though the house in the movie was at Madison and 93rd Street- it no longer stands- I went hunting for it myself). Scientist Charles Ogden Roper (Gene Lockhart) is stealing secrets from the A bomb project, which the agents refer to as Process 97. Dietrich brings down the whole house of cards. Lloyd Nolan plays his FBI handler, and an unbelievably young E.G. Marshall plays a morgue attendant. The last shots of the film is real footage of the actual spies walking into the Federal Courthouse in Manhattan. I have cribbed heavily from the movie's commentary by Eddie Miller. Link above is to imdb.