Julius and Ethel Rosenberg

The most argued-over case on the list. Julius Rosenberg was spying for the Soviet Union by 1942 and tried to recruit others, including his brother-in-law David Greenglass, who worked at Los Alamos. When the atomic ring unraveled in 1950 with the arrests of Fuchs and Harry Gold, Greenglass implicated Julius, who was arrested on July 17; Ethel followed a month later. Both were convicted of conspiracy to commit espionage on March 29, 1951, and executed at Sing Sing on June 19, 1953. Decrypted Venona cables later confirmed Julius as the agent codenamed LIBERAL. How much Ethel knew or did remains disputed: Greenglass, whose testimony against her was central, later said he testified falsely to protect himself and his wife.