On 24 July 1915, Heinrich Albert, the commercial attaché of the Imperial German Embassy, was doing what many of us do in New York: taking the subway. Then he did something most of us don’t do on the subway in NYC: he fell asleep. He woke with a start right as his train reached his destination and the moment the doors opened he dashed out of the subway car on his way to an appointment. He left his briefcase filled with secret documents aboard the train car and a Secret Service agent who had been tailing him kindly took the briefcase and delivered it to his superiors in the Secret Service.
(Source: Insidious Foes: The Axis Fifth Column and the American Home Front by Francis MacDonnell.)