Another page contained a list of six weather station employees. Only one was female, Ranitskaya. (In Russian, a surname often reveals a person’s gender.) Could that be Olga?

Ms. Eroshok wrote to the archives of 15 different secret police agencies, courts and other organizations in Russia, Ukraine and Kazakhstan, requesting information about one Olga Ranitskaya. The central archives wrote back that they had no information. Her quest was a typical example of how difficult it can be to verify information about the victims of Soviet brutality.

Frustrated, she wrote an article in Novaya Gazeta about her hunt, and clues trickled in. She got lucky.

In Israel, Inna A. Nogotovich, a Russian immigrant occasionally nostalgic for home culture, read the article by chance and got in touch with Ms Eroshok. Ms. Nogotovich was Ms. Ranitskaya’s niece, and she filled in many blanks.

Then Ms. Eroshok heard from an even more unexpected quarter. Vasily Khristoforov, then head of the notoriously secretive archives of the F.S.B., or Federal Security Service, the successor agency to the Soviet secret police, offered to help. He contacted several security agency archives, including one in Ukraine, and obtained the records of Ms. Ranitskaya’s interrogation after her arrest.

From this, Ms. Eroshok was able to piece the story together. Ms. Ranitskaya was a Ukrainian Jew born in Kiev in 1905 to two professionals. The family name was Rabinovich, which she eventually changed. Ending her education early, she married a Communist Party official and had a son, Sasha, in 1925. She divorced and married another party official.