For much of their lives, Michael and Robert Meeropol, the sons of Ethel and Julius Rosenberg, who were sentenced to death in 1953 after being convicted of passing atomic secrets to the Soviet Union, fought to have their parents' innocence recognised.

In particular, they always insisted that their mother was wrongfully convicted.

The release of a testimony by the late David Greenglass - Ethel Rosenberg's brother, who implicated his sister as a spy at her trial - by a federal court in New York City last week gives them new ammunition.

When testifying before a grand jury in 1950 - more than six months before his sister's trial - Greenglass appeared to deny that his sister engaged in any espionage, which he only attributed to Julius Rosenberg and others. Greenglass, who was a spy himself, served nine years in prison for treason.

"I said before, and say it again, honestly, this is a fact: I never spoke to my sister about this at all," Greenglass said.

"I have always thought the Greenglasses were despicable people," said Michael Meeropol. "They didn't just confess and tell the truth - they made stuff up to make our parents look worse."

Greenglass may well have lied when he told the court that Ethel Rosenberg had typed up information that was passed on to the Soviet Union - the piece of information that would send his sister and brother-in-law to the electric chair.

Some might say that Ethel should have testified against her husband given that her first responsibility was towards their children.

But did she really have a choice? No, argued Mr Meeropol.

"What was her alternative? Repudiate her marriage by turning on my father?" he said. "Especially since they knew much of the case against both of them was false. You cannot 'partially confess', which is what they would have had to do.

"History has already decided she was framed and innocent. Some day, maybe, the US government will officially exonerate her," said Mr Meeropol.