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.