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 Ethel Rosenberg's brother, David Greenglass, whose name to many became synonymous with betrayal.

For his role in the conspiracy, Greenglass, an army sergeant who had stolen nuclear intelligence from Los Alamos, New Mexico, went to prison for almost a decade, then changed his name and lived quietly until a journalist tracked him down. He admitted then, nearly half a 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.

Greenglass died on July 1st, according to a family member. He was 92. His family did not announce his death; the New York Times learned of it in a call to the nursing home where he had been living under his assumed name. Greenglass's wife, Ruth, who had played a minor role in the conspiracy and also gave damning testimony against the Rosenbergs, died in 2008.

In today’s world, where spying has more to do with greed than ideology, the story of David Greenglass and the Rosenbergs is an enduring time capsule from an age of uncertainties – of world war against fascism, Cold War with the Soviets, and shifting alliances that led some Americans to embrace utopian communism and others to denounce such ideas, and their exponents, as unAmerican.

Greenglass, who grew up on the lower-east side of Manhattan in a household that believed Marxism would save humanity, was an ardent, preachy communist when drafted by the army in the second World War, but no one in the barracks took him very seriously, much less believed him capable of spying.

Manhattan Project

He was not well-educated, but his skills as a machinist – and pure luck – led to his assignment in 1944 to the Manhattan Project at Los Alamos, where the United States’s first atomic bombs were being developed. After being picked to replace a soldier who had gone awol, he lied on his security clearance report and was assigned to a team making precision moulds for high-explosive lenses used to detonate the nuclear core.

When Julius Rosenberg, already a Soviet spy, learned of his brother-in-law’s work, he recruited him. Security was often lax at Los Alamos, with safes and file cabinets left unlocked and classified documents lying on desks. Greenglass had no need for Hollywood spy tricks. He kept his eyes and ears open and, in mid-1945, sent Julius Rosenberg a crude sketch and 12 pages of technical details on the bomb.

That September, after the Japanese cities Hiroshima and Nagasaki were destroyed with atomic bombs, ending the war, David and Ruth Greenglass visited the Rosenbergs' apartment in New York. What happened there later became a matter of life and death, for as David Greenglass delivered his latest spy notes, a woman – either his wife or his sister – sat at a Remington typewriter and typed them out.

The significance of that act did not become evident for five years. By then the Soviet Union, once a US ally, had become a Cold War foe, witch hunts for suspected communists were under way, and spy networks were being broken up. Klaus Fuchs, a physicist who had worked at Los Alamos, was caught, and named Harry Gold as a courier. Gold then named the Greenglasses and the Rosenbergs, who were arrested in 1950.

David Greenglass admitted passing secrets to Julius Rosenberg, but refused at first to implicate his sister. But just before the Rosenberg trial, Greenglass changed his story. Told that Ruth had informed FBI agents that Ethel had typed his notes, he supported his wife’s account and agreed to testify against his sister and her husband.

Greenglass was under intense pressure. He had not yet been sentenced, and his wife, the mother of his two small children, faced possible prosecution, though her role had been minimal. In federal court in Manhattan in 1951, David Greenglass’s testimony – corroborated by that of his wife – clinched the case against Julius Rosenberg and implicated Ethel Rosenberg.

Referring to Ethel Rosenberg in ringing hyperbolic phrases, the chief prosecutor, Irving H Saypol, declared, "Just so had she, on countless other occasions, sat at that typewriter and struck the keys, blow by blow, against her own country in the interests of the Soviets."

Spy conspiracy

The jury found the Rosenbergs guilty of espionage conspiracy, and the presiding judge,

Irving R Kaufman

, sentenced them to death. Appeals failed, and the Rosenbergs, who rejected all entreaties to name collaborators and insisted they were not guilty, were executed in New York’s Sing Sing prison on June 19th, 1953. A co-defendant,

Morton Sobell

, was also convicted and was imprisoned for 18 years.

Ruth Greenglass was not prosecuted. David Greenglass was sentenced to 15 years, but was released in 1960 after 9½ years. He rejoined his wife and for decades lived quietly in the New York area, working as a machinist and inventor. A 1983 book by Ronald Radosh and Joyce Milton, The Rosenberg File: A Search for the Truth, rekindled interest, concluding that Julius Rosenberg was a dedicated spy but that his wife had played only a minor role, and raising questions about the evidence and the government's tactics in the case. Radosh and Sol Stern also interviewed Greenglass for an article in the New Republic.

Sam Roberts, a New York Times editor and reporter, later found David Greenglass and, after a 13-year effort, obtained 50 hours of interviews that led to a book, The Brother: The Untold Story of the Rosenberg Case. In the book, David Greenglass admitted that, to spare his wife from prosecution, he had testified that his sister typed his notes. In fact, he said, he could not recall who had done it.

“I don’t remember that at all,” David Greenglass said. “I frankly think my wife did the typing, but I don’t remember.” He said he had no regrets. “My wife is more important to me than my sister. Or my mother or my father, OK? And she was the mother of my children.”

In a 2008 interview with Roberts, Sobell admitted that he had given military secrets to the Soviet Union, and concurred in what has become a consensus among historians: that the Greenglass-Rosenberg atomic bomb details were of little value to the Soviets, except to corroborate what they already knew, and that Ethel Rosenberg had played no active role in the conspiracy.

Sister’s suitor

David Greenglass was born on the lower-east side on March 2nd, 1922, to immigrants from

Russia

and Austria. He was 14 when he met Julius Rosenberg, who began courting Ethel, who was seven years older than David, in 1936. The Rosenbergs were married in 1939.

David graduated from Haaren High School in 1940 with only fair grades. He attended Brooklyn Polytechnic Institute, but dropped out. Greenglass and Ruth Printz, who had been neighbours, childhood sweethearts and members of the Young Communist League, were married in 1942. They had a son and a daughter, who survive him. He had several machinist jobs before being drafted in 1943, and the army put his skills to use. He fixed tank motors, inspected equipment and worked on ordnance in California and Mississippi. He was also assigned to classified work at Oak Ridge, Tennessee, where uranium was being enriched for a secret weapon.

Glowing reports

To pass his security clearance for the most sensitive work of the war at Los Alamos, Greenglass disguised or omitted communist associations in his background. For character and work references, he advised the writers – all friends – on how to respond, and only glowing reports came back. “All evidence indicates subject to be loyal, honest and discreet,” army intelligence reported.

Everywhere – even at Los Alamos – he preached communism, trying to persuade fellow GIs and co-workers that they would someday prosper in a utopian society free of squalor and injustice. Letters to his wife, some signed “Your Comrade,” also sprinkled dialectics among the endearments. “We who understand,” he wrote, “can bring understanding to others because we are in love and have our Marxist outlook.”

The deaths of David and Ruth Greenglass, like those of the Rosenbergs more than 60 years ago, are unlikely to end public fascination with the case, whose betrayals have been woven into American culture. In Woody Allen's film Crimes and Misdemeanours, the character played by Allen says dryly that he still has feelings for his vile brother-in-law.

“I love him like a brother,” he says. “David Greenglass.” – (New York Times service)