David Greenglass, handcuffed and accompanied by a U.S. marshal, right, arrives at Federal Courthouse in New York City, on July 31, 1950. (AP)

David Greenglass, confessed member of the infamous Rosenberg atomic spy ring, died July 1 at 92, more than a half-century after his better-known sister, Ethel Rosenberg, went to the electric chair in part for what he later claimed was his false testimony against her.

The death was confirmed by Sam Roberts, a New York Times reporter who wrote “The Brother” (2001), which details much of the historic espionage story. The Times first reported the death, citing sources at a nursing home where he long had lived under an assumed name. No other details were provided.

In the epic Cold War espionage case that transfixed America amid frenzied anti-communist fervor, Ethel Rosenberg and her husband, Julius, were executed in 1953 after being convicted of conspiracy to pass atomic bomb secrets to the Soviet Union during and after World War II.

Mr. Greenglass, portrayed by many who knew him as hard-nosed and pragmatic, pleaded guilty in exchange for testifying against the more ideological Rosenbergs. He served 10 years of a 15-year sentence and was released from federal prison in 1960. Another defendant, Morton Sobell, was convicted and served 18 years of a 30-year term.

Mr. Greenglass’s wife, Ruth, also testified against the Rosenbergs and — as an unindicted co-conspirator — avoided prison time.

Ethel and Julius Rosenberg are shown during their trial for espionage in New York City in 1951. They were later executed. (AP)

The executions formed a vivid backdrop for not only the nation’s obsession with domestic communist skulduggery and Russia’s entry into the nuclear club in 1949, but also the bitterly personal split within the Rosenberg-Greenglass families that tested their mutual trust and loyalty.

In addition, because the defendants were Jewish, many Americans feared the case would incite a wave of anti-Semitism — compounded by the irony that both the trial judge and chief prosecutor also were Jewish.

While incarcerated, Mr. Greenglass was shunned by fellow inmates as a traitor and a particularly repugnant kind of stool pigeon — a view shared by many in the wider public.

“Any man who will testify against his own blood and flesh, his own sister, is repulsive, is revolting,” declared Emanuel Bloch, the Rosenbergs’ principal defense attorney, summing up the case to the jury in March of 1951. “He is the lowest of the lowest animals that I have ever seen.”

But chief federal prosecutor Irving Saypol countered that the gravity of stealing vital national secrets “transcends any family consideration” and that David and Ruth Greenglass courageously “tried to make amends for the hurt which has been done to our nation and to the world.”

After prison, Mr. Greenglass lived in almost total anonymity under an assumed name, dodging news reporters and the general public for decades.

In a rare interview published in 2001, he asserted for the first time that he had lied in court by magnifying Ethel Rosenberg’s role in the spy ring, chiefly to protect his wife from prosecution.

His disclosure, obtained by Times reporter Roberts, centered on handwritten notes by Mr. Greenglass containing atomic bomb data from the super-secret Manhattan Project in New Mexico that the spy group wanted typed in more legible form.

Mr. Greenglass and his wife testified that Ethel Rosenberg transcribed the notes on her portable Remington typewriter — a crucial “overt act” in the federal indictment tying Ethel more fully to the conspiracy.

In his interview with Roberts years later, Mr. Greenglass said he had no recollection at the time of Ethel typing the notes. “I don’t remember that at all,” he said. “I frankly think my wife did the typing, but I don’t remember.”

So why did he sacrifice his sister? His explanation: During a pretrial FBI interrogation, his wife had indicated that Ethel did the typing and would testify so at trial.

“So what am I gonna do, call my wife a liar?” he told Roberts. “My wife is my wife. I mean, I don’t sleep with my sister, you know. . . . My wife is more important to me than my sister.”

Mr. Greenglass’s statements, part of more than 50 hours of tape-recorded interviews, were incorporated into “The Brother.” He also recounted his false testimony on television later in 2001, appearing heavily disguised on the CBS News program “60 Minutes II.”

In retrospect, he blamed the Rosenbergs’ deaths in part on their refusal to confess to spying and to name other conspirators. Roberts asked him why they refused.

“One word,” he replied. “Stupidity.”

David Greenglass was born on March 2, 1922, in New York City, son of Russian and Austrian-German immigrants Barnet Greenglass and Theresa “Tessie” Feit. David was the youngest of their three children. Ethel was born in 1915 and Bernard in 1917. An older half-brother, Samuel, was born in 1909 to Barnet Greenglass’s first wife, Beckie, who died in 1911.

He grew up on the Lower East Side of Manhattan, a largely impoverished and densely populated area of immigrants and their children, where left-wing ideas and activities found support among a substantial number of residents. Julius Rosenberg and David’s teenage sweetheart and future wife, Ruth Printz, also grew up in the swirling world of militant unionism and protests .

Baby-faced with black curly hair, Mr. Greenglass joined the Young Communist League in the late 1930s but never moved up to full membership in the American Communist Party, as did his more politically driven brother-in-law.

“To me it was like a peripheral thing,” he told Roberts.

He and Ruth married in November 1942, during World War II, when Ruth was 18. They had two children, Barbara and Steven.

Mr. Greenglass was drafted into the Army in 1943 and, after being lightly vetted by security agents, was assigned as a machinist to the Manhattan Project in Los Alamos, N.M., where scientists were developing the nation’s first atomic bomb.

When Julius Rosenberg learned this, he recruited his brother-in-law to gather information — documents, bomb-part specifications, names of scientists — for Rosenberg to pass on to Soviet agents.

Mr. Greenglass complied, delivering notes from conversations with fellow workers about aspects of atomic research and a sketch of what he said was an implosion-type nuclear device.

Authorities did not close in on Mr. Greenglass until after the war, in 1950. The FBI first caught German-born physicist and spy Klaus Fuchs, who identified American Harry Gold as a courier. Gold, in turn, pinpointed both the Greenglasses and the Rosenbergs.

The notes and sketch turned out to be of little use to the Soviets, according to scientists and administrators who worked at Los Alamos. Mr. Greenglass’s low rank, scant scientific knowledge and lack of technical training limited his usefulness, they said.

His information “was of minor value,” Gen. Leslie R. Groves, the senior military officer in charge at Los Alamos, told the Atomic Energy Commission in 1954.

The implosion bomb sketch was “garbled, ambiguous and highly incomplete,” Manhattan Project scientist Henry Linschitz said.

The Soviets, in fact, received far higher-quality data, and sooner, from other spies in New Mexico, including Fuchs.

Nevertheless, Roberts wrote in his book, Mr. Greenglass clung to the belief that he not only helped the Soviets develop the bomb, but also reduced the chances of another world war by contributing to a balanced nuclear deterrence.

Mr. Greenglass lived out the bulk of his life in the New York metropolitan area in carefully guarded anonymity, earning a modest income as a machinist and inventor of electric gadgets. His wife, who worked as a legal secretary, died in 2008 at 83. No information on survivors was immediately available.

The Rosenbergs were executed at Sing Sing prison in Ossining, N.Y., and left behind two young sons, Robert and Michael, who were adopted by another couple, Abel and Anne Meeropol. The children never again had contact with Mr. Greenglass. He was “a sleazy, despicable person,” Robert Meeropol told Roberts, “and I don’t doubt he is despicable to this day.” (Meeropol went on to wrote his own book, “An Execution in the Family: One Son’s Journey.”)

Roberts once asked Mr. Greenglass what he would want his own obituary to say. He answered: “I was a good father. A good husband. A good son. A good brother. Born in a time which tore people’s souls.”

Paul Valentine is a novelist and former Washington Post reporter.