Ruth Greenglass, whose damning testimony in the Rosenberg atomic-bomb spy case of the early 1950s helped lead to the execution of her sister-in-law Ethel Rosenberg, died on April 7. She was 83.

Mrs. Greenglass’s testimony was later called into question.

Along with her husband, David Greenglass  Ethel’s brother and a central figure in the case  Mrs. Greenglass had lived in the New York metropolitan area under an assumed name for more than four decades. Her death was revealed in court papers on June 23.

That day, in an unexpected response to a suit by historians, the federal government agreed to release secret grand jury testimony, 57 years after Julius and Ethel Rosenberg were convicted of conspiracy to commit espionage. The government, however, consented to release the testimony of only 35 of the 45 witnesses; those who are dead or have consented to the release. Mrs. Greenglass was listed as one of the deceased; her death was confirmed by the United States Attorney’s Office in Manhattan and through Social Security records. Mr. Greenglass survives her.

The Rosenberg investigation can be traced to 1945, when a Soviet cipher clerk, Igor Gouzenko, defected to the West and stunned intelligence officials by revealing that the Russians were engaged in extensive spying against their wartime allies. At the time, David Greenglass was an Army sergeant assigned as a machinist to the Manhattan Project, the program to develop the atomic bomb, at Los Alamos, N.M.