David Greenglass (March 2, 1922 – July 1, 2014) was an American machinist who worked on the Manhattan Project and was an atomic spy for the Soviet Union.

In order to pass his security clearance, he disguised or omitted details of his communist associations and had friends write glowing references.

[4][5] Julius Rosenberg, who had married Greenglass' sister, Ethel, in 1939, had become an agent for the Soviet Union (USSR), working under Alexander Feklisov.

[6] On September 21, 1944, Feklisov reported to Moscow: "They are young, intelligent, capable, and politically developed people, strongly believing in the cause of communism and wishing to do their best to help our country as much as possible.

"[7] David wrote to his wife, Ruth: "My darling, I most certainly will be glad to be part of the community project [espionage] that Julius and his friends [the Soviets] have in mind.

[9] Greenglass began to pass nuclear secrets to the USSR via the courier Harry Gold, and more directly with a Soviet official in New York City.

[10] According to the Venona project intercepts decrypted by the National Security Agency between 1944 and some time in the 1970s, Greenglass and his wife Ruth were given code names.

[11] Greenglass turned down requests from the Los Alamos Laboratory (and Rosenberg) to work on the Operation Crossroads nuclear tests at Bikini Atoll because he wanted to be with Ruth.

[12][a] On February 14, 1950, Ruth, who was pregnant with their second child, came too close to the gas heater in their Lower East Side apartment, and her nightgown caught on fire.

He was already aware that the UK and US intelligence agencies had discovered that a Los Alamos theoretical physicist, Klaus Fuchs, had spied for the USSR during the war.

The Rosenbergs' defense attorney, Emanuel H. Bloch, attempted to convince the jury that his clients were concerned about issues of national security, but he failed.

[22] In March 1953, three months before the Rosenbergs' executions, he wrote a letter for his attorney to deliver to US President Eisenhower asking for their sentences to be commuted to prison terms so that they would have an opportunity to confess.

He described his own testimony as "an act of contrition for the wrong I had done my country, my family and myself" and explained how he now viewed its consequences: "Here I had to take the choice of hurting someone dear to me, and I took it deliberately.

In 1996, Greenglass recanted his sworn testimony in an interview with The New York Times reporter Sam Roberts and stated he had lied under oath about the extent of his sister's involvement in the spying plot in order to protect his wife.

U.S. District Judge Alvin Hellerstein declined to order the release of the testimony of Greenglass and other surviving witnesses who withheld their consent or could not be located.

His death was not publicly announced by his family and was only discovered on October 14, 2014, when a New York Times reporter called the nursing home where he had been living under an assumed name.