When women kill, which they don't do very often, the motive can be quite different from their male counterparts. Learn what situations make women snap, making murder feel like the only option they have.
Why men commit more murders then women is a loaded question. It probably has something to do with a natural, evolved propensity for violence needed to gain social status, resources and control over a sexual mate. Women, on the other hand, are the natural nurturers and caretakers which could make them less "hard-wired" for violence.