More than six decades later, the prosecution of Ethel Rosenberg remains one of America’s most controversial criminal cases: Her conviction — and eventual execution — for joining in her husband Julius’s espionage conspiracy rested largely on trial testimony from her younger brother.

But in private testimony to a grand jury seven months before the 1951 trial, Mrs. Rosenberg’s brother, David Greenglass, never mentioned involvement by his sister in Mr. Rosenberg’s delivery of atomic secrets to Soviet operatives, according to a grand jury transcript released Wednesday.

While not definitive proof that he lied at trial, Mr. Greenglass’s omission — and his assertion before the grand jury that he had never even discussed espionage with his sister — provides further evidence to Mrs. Rosenberg’s defenders who believe that she was unfairly convicted, and that her brother, under pressure from prosecutors, had doomed her with concocted testimony to spare his own wife from prosecution.

At the trial, Mr. Greenglass, who had been an Army machinist assigned to Los Alamos, N.M., where the atomic bomb was developed, testified that in September 1945 he had delivered bomb secrets to his brother-in-law in the Rosenbergs’ Lower East Side apartment. There, he said, his sister typed his handwritten notes for delivery to the Russians.