This entry carries a warning rather than a biography. The story of Madame Popova appears in English-language true crime encyclopedias in a fixed form: a Russian woman who for thirty years operated a service killing the violent husbands of women who came to her, sometimes with arsenic, sometimes with a hired man, who charged little or nothing, who was denounced by a client stricken with remorse, who confessed to around three hundred killings and was shot by firing squad before a crowd in March 1909.
There is no contemporary Russian source for any of it. No trial record, no arrest record, no name beyond the honorific, no town, no newspaper account in the Russian press of an execution that would have been an enormous story. The account traces back through the same chain of Anglophone compilations that produced the Vera Renczi story, and it has the same shape: an exotic foreign murderess, a very round number, and no documents.
It is possible that something real sits underneath it. Rural Russia at the turn of the century had a genuine and documented phenomenon of women poisoning violent husbands, and there were prosecutions. But the figure of three hundred and the murder-for-hire business are not evidenced.
This archive keeps the entry because the name is asked about, and states plainly that nobody has produced a source. If a Russian archival document turns up, this should be rewritten.