Frieda combines the biographies of several women. Two were case studies in Swiss psychologist August Forel's book Sexual Questions (1908). Bulgakov's notes have an excerpt from this book: "Frieda Keller--killed her boy. Koniecko--suffocated her baby with a handkerchief" (ORGBL, f. 562, k. 8, ed. khr. 1 in S 540). Frieda Keller (b. 1879) worked as a seamstress and waitress in St. Gallen. She was raped by the owner of the cafe and gave her baby up to an orphanage. But when the boy was returned to her at age 5 she strangled him with a string and buried him in a shallow grave. She was sentenced to life in prison. Because of her modesty and good behavior, public opinion in Switzerland turned in her favor, and Forel himself wrote that he hoped "poor Frieda Keller" would soon be released. He also wrote of the 19 year old Silesian worker Koniecko, who gave birth to a child and suffocated it by stuffing a handkerchief in its mouth in 1908. Like Margarita, Forel suggests that the real murderer is not the mother, but the father who abandoned the pregnant woman. But the date and the name suggest Keller as the prime prototype (she gave birth in 1899, 30 years before the time of the novel). Frieda's story also has some features in common with Goethe's Gretchen in Faust, since she too kills her child and is sentenced for the murder.