Q, I understand that a widow whose two previous husbands died is called a Katlanis, literally “a killer”, a woman who is dangerous to marry or forbidden to marry (not sure which). I understand that the reason is because it is suspected that her Mazal is that her husbands die.
What if a woman actually murdered her first husband? Then she is for sure a Katlanis. Is it forbidden to marry her?
A. Shulchan Aruch (Even Haezer 9: 1) rules that a woman that was previously married to two men and both died, should not marry again. However, if she did get married she could stay with her husband. Remah (ibid.) adds that the above applies only if they died a natural death, but not if one of them was killed.
Poskim disagree as to the severity of this prohibition. Beis Shlomo (18), Yashresh Yaakov (Yebamos 26a), Ksav Soffer (13) an others (quoting Ritvo), maintain it is due to the danger of life involved and it is a Biblical edict. They add that the story of Yehuda and Tamar, seems to give echo to this prohibition. And they thus explain why even after two cases the proscription applies, when normally a chazaka requires three instances, since Chamiro Sakanto, we address danger of life more severely than a common prohibition.
However, Beis Yitzchok (1: 46), Besomim Rosh (276), Teshubos Harematz and others maintain it is only a Rabbinical prohibition, and thus after the fact she may remain married.
There are two reasons mentioned in the Talmud as to the nature of this decree. It is due to her bad mazal and defective luck that affects her husband too, or to the marital relations involved. The difference may include whether she actually got married or was only engaged, the husband was killed and was his fault, and other cases.
As to the question where the woman murdered her husband, (assuming that it was in self defense and she is set free or it was accidental), it would seem to depend on the above reasons mentioned and you would still need two instances.
Therefore, Horav Shlomo Miller’s Shlit’a opinion is that she is permitted to remarry.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a