David Greenglass, who served 10 years in prison for his role in the most explosive atomic spying case of the Cold War has died aged 92.

He gave testimony that sent his brother-in-law and sister, Julius and Ethel Rosenberg, to the electric chair in 1953.

Greenglass - who admitted decades after the trial that he lied on the stand about his own sister - died in New York City on July 1, according to the Rosenbergs' sons, Michael and Robert Meeropol.

The Rosenbergs were convicted in 1951 of conspiring to steal secrets about the atomic bomb for the Soviet Union and were executed at New York's Sing Sing prison, insisting to the very end they were innocent.

After his release from prison in 1960, Greenglass lived under an assumed name in the New York borough of Queens, hoping to be forgotten for his part in a McCarthy-era controversy that is still furiously debated to this day.

A spokeswoman for the Meeropols, Amber Black, said the brothers were aware of their uncle's death last summer but did not seek media attention and received no inquiries at the time.

Greenglass, charged as a co-conspirator, testified for the government that he had given the Rosenbergs research data obtained through his wartime job as an Army machinist at Los Alamos, New Mexico, the headquarters of the top-secret Manhattan Project to build the atomic bomb.

He told of seeing his older sister transcribing the information on a portable typewriter at the Rosenbergs' New York apartment in 1945.

That testimony proved crucial in convicting Ethel along with her husband.

In 2001, Greenglass was quoted in the book The Brother by Sam Roberts as saying he had not actually seen Ethel typing and knew of it only from his wife, Ruth.

For the prosecution, however, the typewriter "was as good as a smoking gun in Ethel Rosenberg's hands," Roberts wrote.

"Without that testimony, I believe she would not have been convicted, let alone executed," Roberts said yesterday.

In the book and a CBS interview, Greenglass shrugged off any notion of a betrayal. He said he lied to assure leniency for himself and keep his wife out of prison so she could care for their two children.

"As a spy who turned his family in ... I don't care. I sleep well," Greenglass said in the interview, adding that "stupidity" had kept the Rosenbergs from possibly saving themselves by admitting guilt.

Greenglass said while history might blame him for the Rosenbergs' deaths, he had not known that would be their fate - and that in any case, his own family came first.

In a statement yesterday, the Rosenbergs' sons said David and Ruth Greenglass were the ones who passed atomic secrets on to the Soviets.

They then "pinned what they did on our parents - a calculated ploy to save themselves by fingering our parents as the scapegoats the government demanded".

Greenglass was born in New York in 1922. After Army service in the Second World War, including the Los Alamos assignment, he and Julius Rosenberg became partners in a machine shop.

The business failed, and a Rosenberg lawyer later claimed that led Greenglass to seek revenge on his brother-in-law.

In fact, David and Ruth Greenglass, like the Rosenbergs, were active communist sympathisers, having joined the Young Communist League in 1943. Both couples believed that the Soviet Union should have the bomb if the US did.

At trial, the Greenglasses said Julius Rosenberg had recruited David Greenglass as a spy and arranged for him to feed stolen atomic research and a detonator to a go-between, Harry Gold. Gold also was later convicted.

Greenglass served 10 years of a 15-year sentence for espionage. After his release, he lived with his family in anonymity as controversy over the Rosenberg case continued over the decades.

Greenglass remained estranged for the rest of his life from the Rosenbergs' sons, who were six and 10 when their parents were executed. The brother later took their adoptive parents' surname, Meeropol.