The Duquesne Spy Ring is the largest espionage case in United States history that ended in convictions. A total of 33 members of a German espionage network headed by Frederick "Fritz" Joubert Duquesne were convicted after a lengthy investigation by the Federal Bureau of Investigation (FBI). Of those indicted, 19 pleaded guilty. The remaining 14 were brought to jury trial in Federal District Court, Brooklyn, New York, on September 3, 1941; all were found guilty on December 13, 1941. On January 2, 1942, the group was sentenced to serve a total of over 300 years in prison.