The following text refers to a prisoner held an old castle at Beira, Mozambique, built about 1510 that was, at the time of the author’s visit in 1914, used as a prison.
EXCERPT: These convicts were of all races but mostly from India. One had been the mayor of some town there. One a white woman who was kept behind bars, of about 50 years of age, had murdered two husbands, in Portugal and on the west coast respectively, the second way too shocking to mention. Yet she seemed to retain some refinement as she had flowers and a canary bird in her window. Mad probably. She most politely asked me to come up to see her but I declined the honour.
(Author), (Editor), Diary of an African Journey: The Return of H.Rider Haggard, 2001, p. 256]
For links to other cases of woman who murdered 2 or more husbands (or paramours), see Black Widow Serial Killers.