Julius and Ethel RosenbergDuring and after World War II, Julius Rosenberg spied on behalf of the Soviet Union. His brother-in-law was a technician fabricating components for the Manhattan Project. Julius persuaded him to hand over atomic bomb secrets, which he then relayed to the U.S.S.R.
Both Julius and his wife Ethel were arrested in 1950. J. Edgar Hoover called it the "crime of the century." In the end, they were convicted of conspiracy to commit espionage for the Soviets. The married couple was executed in the Electric Chair at Sing-Sing Prison.
The Rosenbergs had been active members of the American Communist Party; Julius was chairman of Branch 16B of the Industrial Division, whose meetings were held in their apartment. They ostensibly quit the party in 1943 after Julius got a civilian job in the U.S. Army Signal Corps inspecting radar equipment.
Then Julius met his KGB spymaster, Aleksandr Feklisov, for the first time. Over the next three years they had at least 50 such meetings, according to Feklisov. Julius handed over the schematic diagram for a lens mold, as well as a working specimen of a proximity fuse. Julius got this stuff from his brother-in-law, David Greenglass.
When he got picked up by the FBI, Greenglass accused his older sister Ethel of typing up an incriminating report for the KGB. In all likelihood, it was probably David's wife Ruth. But why take your wife to prison, when you can send your sister instead? During a 2001 interview, Greenglass was unapologetic:
"I would not sacrifice my wife and my children for my sister. How do you like that? And that's what I told the FBI. I said, 'If you indict my wife, you can forget it. I'll never say a word about anybody.'"