Here's what we know: Julius and Ethel Rosenberg were executed in 1953 for selling U.S. nuclear secrets to the Soviet Union after one of the most sensational Cold War-era espionage trials. They were convicted in 1951 owing, largely, to the testimony of David Greenglass, Ethel Rosenberg's brother.

Here's what we don't know: How credible Greenglass' testimony was in court.

Greenglass himself spent nearly a decade in prison for his role in the conspiracy. The Army sergeant stole nuclear intelligence from Los Alamos, N.M., and said he passed it on to the Rosenbergs. At the trial, he said Ethel Rosenberg typed his notes that were then given to the Russians.

But decades later, Greenglass, who died in 2014, told New York Times reporter Sam Roberts he had lied to protect his wife, Ruth Greenglass, and suggested it was she who had typed up the notes. Ruth Greenglass died in 2008.

Today the National Security Archives released Greenglass' grand jury testimony, lending weight to his account to Roberts.

In the testimony from Aug. 7, 1950, Greenglass is asked whether Ethel Rosenberg asked him to stay in the Army so he could continue providing information from Los Alamos. His reply: "I said before, and say it again, honestly, this is a fact: I never spoke to my sister about this at all."

But at trial, a year later, he put Ethel at the center of the conspiracy. The documents released today show it was Ruth who played a far more pivotal role.

The testimony, which was sealed for more than six decades, was released upon the order of Judge Alvin Hellerstein, who cited its historical significance.

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