The FBI’s First Double Agent

William “Sebold, a German native born in 1899, served in his nation’s army during World War I then lived in the United States and South America before becoming a naturalized U.S. citizen in 1936. Three years later, during a visit to his homeland, Sebold was recruited to spy on the United States for Germany. The Nazis, who had learned he once worked briefly at an airplane factory in California, threatened him if he failed to cooperate. Sebold secretly went to the American consulate in Cologne...