The following suggests that two husbands were murdered, plus two “lovers,” before a fifth victim managed to escape his fate. So far the two articles below are the only reports top be located. More detailed articles are expected to be available eventually. Each article gives a different spelling. It is quite possible that neither is quite accurate (perhaps “Büchmann”).
FULL TEXT (Article 1 of 2): Mme. Backman has been arrested at Zurich for poisoning five husbands. We think she should of told that this sort of thing has got to be stopped.
[Untitled, The Sunday Mirror, Perth, W.A., Australia), Sep. 12, 1920, p. 4]
The question of the mysterious deaths of two lovers of Buchmann, though mentioned at the trial, was not pressed by the Court, which had sufficient evidence on the first two charges. The jury promptly returned a verdict of guilty, the foreman adding that the woman was a Swiss Borgia without scruples of honour. The Cantonment Zurich has abolished capital .punishment by the guillotine, and the murderess left the Court smiling between two gendarmes.
[“Poisoned Two Husbands.” The Auckland Star (New Zealand), Feb, 26, 1921, p. 19]
For links to other cases of woman who murdered 2 or more husbands (or paramours), see Black Widow Serial Killers.