Lack of empathy + high agressivity + issues during development (as much as NAMI mommies refuse to admit it, parent has an effect on development of individual).

Again, I don't really think evil has to do with mental illness. I would use it for the extreme cases (Hitler, Milosevic, Pol Pot, that Russian guy that looks like Voldermort...). Or extremelly sadistic or just effed up beings (some try to pull the schizo card on Breivik :/)