Pretty ugly are the numbers regarding relatives, ugh:
28.3% of females kill their spouses, only 6.8% of males do.
10.4% of females kill their stepchildren or children, only 2.2% of males do that.
I saw a bizarre and disturbing statistic that was uncovered from medieval German death records. Researchers were sifting through the old data looking for child mortality predictors, and the leading indicator that popped out was whether the baby's paternal grandmother lived in the home. After much head scratching, they realized that the father's live-in mothers must've been killing the babies, probably if they suspected that their son wasn't the real father. Grimm's Fairytales had old German ladies pegged.
One, the study set the authors derived wasn't from "medieval Germany", it was from 17-18th century Germany and what was then the Kingdom of Hanover. Two, if you actually read the paper, you'd know that mass infanticide was never a conclusion made by the author. Their suggestion was rather that it was due to pressure, stress and conflict between the in-law and the mother, the same effect which latter papers has also observed in several countries including Japan and Canada