David Greenglass, Spy Who Helped Seal the Rosenbergs’ Doom, Dies at 92

It was the most notorious spy case of the Cold War — the conviction and execution of Julius and Ethel Rosenberg for passing atomic secrets to the Soviet Union — and it rested largely on the testimony of Ms. Rosenberg’s brother, David Greenglass, an Army sergeant who had stolen nuclear intelligence from Los Alamos, N.M.

For his role in the conspiracy, Mr. Greenglass went to prison for almost a decade, then changed his name and lived quietly until a journalist tracked him down. He admitted then, nearly a half-century later, that he had lied on the witness stand to save his wife from prosecution, giving testimony that he was never sure about but that nevertheless helped send his sister and her husband to the electric chair in 1953.

Mr. Greenglass, whose name to many became synonymous with betrayal, died on July 1, a family member confirmed. He was 92.