WASHINGTON — The brother of Ethel Rosenberg, who was a star trial witness against his sister and brother-in-law in a sensational Cold War atomic spying case, never implicated his sister in an earlier appearance before a grand jury and said that they had never discussed her role “at all,” according to secret court records unsealed Wednesday.

The revelation may heighten public suspicion that Ethel Rosenberg was wrongly convicted and executed in an espionage case that captivated the country at the height of the McCarthy-era frenzy about Communist allegiances.

Rosenberg and her husband, Julius, were put to death in 1953 after being convicted of conspiring to pass secrets about the atomic bomb to the Soviet Union, though they maintained their innocence until the end.

Historians and lawyers who reviewed the transcript said it appears to lend support to both sides of a dueling narrative – that Ethel Rosenberg was framed in an overzealous prosecution even as her husband appears to have played a central role in a sophisticated spy ring.

“You change a black-and-white Cold War narrative – framed or traitors? – into a very nuanced, gray area. Well, both,” said Tom Blanton, director of the National Security Archive at George Washington University, which fought for the records.

The grand jury testimony from David Greenglass, whose damning statements at the 1951 trial helped secure the Rosenbergs’ convictions, had been withheld from public view even as other crucial court records have been unsealed in the last decade. A federal judge in New York ordered the 46-page transcript unsealed following Greenglass’ death last year at age 92.

The transcript presents Julius Rosenberg as a critical figure in an espionage operation that involved shady operatives, code names and a secret signal to help identify couriers for the Russians.

Greenglass told the grand jury how Julius Rosenberg pressed him for secrets and discussed with him the construction and detonation of the atomic bomb. But unlike his trial testimony, Greenglass offered no evidence to the grand jury of Ethel Rosenberg’s direct involvement in the espionage. That suggests Greenglass may later have perjured himself when he said she had an important role, one of her sons said Wednesday.