For women from working-class families or farms in Germany, the occupied zones offered an attractive opportunity to advance themselves, Ms. Lower said.

Image Wendy Lower, who has studied women’s participation in Nazi killings, at the Yad Vashem Holocaust museum in Jerusalem. Credit... Rina Castelnuovo for The New York Times

There were up to 5,000 female guards in the concentration camps, making up about 10 percent of the personnel. Ms. Grese was hanged at the age of 21 for war crimes committed in Auschwitz and Bergen-Belsen; Ms. Koch was convicted of participating in murders at Buchenwald.

Mr. Browning’s book chronicled the role of the German Reserve Police Battalion 101, which helped provide the manpower for the elimination of most Polish Jewry within a year. The book mentions one woman, the young, pregnant bride of one of the captains of the police battalion. She had gone to Poland for a kind of honeymoon and went along with her husband to observe the clearing of a ghetto.

Only 1 or 2 percent of the perpetrators were women, according to Ms. Lower. But in many cases where genocide was taking place, German women were very close by. Several witnesses have described festive banquets near mass shooting sites in the Ukrainian forests, with German women providing refreshments for the shooting squads whose work often went on for days.

Ms. Petri was married to an SS officer who ran an agricultural estate, complete with a colonial-style manor house and slave laborers, in Galicia, in occupied Poland. She later confessed to having murdered six Jewish children, aged 6 to 12. She came across them while out riding in her carriage. She was the mother of two young children, and was 25 at the time. Near naked, the Jewish children had apparently escaped from a railroad car bound for the Sobibor camp. She took them home, fed them, then led them into the woods and shot them one by one.

She told her interrogators that she had done so, in part, because she wanted to prove herself to the men.

She was tried in East Germany and served a life sentence.

Ms. Altvater Zelle went to Ukraine as a 22-year-old single woman and became the secretary of a district commissar, Wilhelm Westerheide. Survivors remembered her as the notorious Fräulein Hanna, and accused her, among other things, of smashing a toddler’s head against a ghetto wall and of throwing children to their deaths from the window of a makeshift hospital.