The Duquesne Spy Ring is the largest espionage case in United States history that ended in convictions. A total of thirty-three members of a German espionage network headed by Frederick "Fritz" Joubert Duquesne were convicted after a lengthy espionage investigation by the Federal Bureau of Investigation (FBI). Of those arrested on the charge of espionage, 19 pleaded guilty. The remaining 14 men who entered pleas of not guilty were brought to jury trial in Federal District Court, Brooklyn, New York, on September 3, 1941; and all found guilty on December 13, 1941. On January 2, 1942, the group was sentenced to serve a total of over 300 years in prison.