Pickup On South Street

from wikipedia. I won't reveal all of the plot
Pickup on South Street is writer-director Samuel Fuller's 1953 film noir released by the 20th Century Fox studio. The film stars Richard Widmark, Jean Peters and Thelma Ritter. Ritter would go on to receive an Academy Award nomination as Best Supporting Actress and Samuel Fuller was awarded the Bronze Lion at the Venice Film Festival for his direction of the picture. In June of 1954, Ritter co-stared alongside Terry Moore and Stephen McNally in a Lux Radio Theatre presentation of the story.

One afternoon, FBI agents Zara and Enyart are following an attractive woman named Candy as she takes the subway in New York City. Unknown to Candy, her wallet is stolen by a "cannon," a pickpocket who targets women, and when she realizes that her wallet is gone, she calls her former boyfriend, Joey. With Enyart following her, she returns to Joey's apartment, where Joey upbraids her for losing the microfilm that she was supposed to deliver to a mysterious higher-up in Joey's organization. Although Candy believes that Joey is selling chemical formulas to a rival firm, he is actually a Communist who is passing on secret government information to an overseas Communist ring. Candy has made several drops for Joey and does not understand why he is so upset about this one, which he had promised would be her last. Joey insists that Candy, an ex-prostitute, use her street connections to locate the pickpocket who accosted her and retrieve the microfilm. Meanwhile, Zara approaches police captain Dan Tiger and explains that the FBI has been following Candy for six months in order to catch the ringleader of the Communist organization. Tiger then summons Moe, a necktie peddler who often sells him information about the underworld. After grilling Zara about the pickpocket's mannerisms, Moe gives Tiger eight names, and Tiger immediately picks out Skip McCoy, a "three-time loser" who was recently released from prison. Moe then tells Tiger that Skip is living in a rundown shack on the waterfront, and Tiger, who bears a grudge against Skip because of his insolence, sends policemen Winoki and MacGregor to arrest him. Skip, who did steal Candy's wallet and has found the microfilm inside, hides it and taunts Tiger about their rivalry.

Trivia: In the opening scene on the subway, a soldier leaves a subway car wearing the "Big Red One" 1st Infantry Division shoulder patch. Director Fuller fought with the 1st Infantry Division during World War II, and later filmed the story in the movie The Big Red One (1980).