Carol Hunt responded to this question as follows: I do not think that you can see who is capable of evil acts from a birthchart. People are not born evil. Charts indicate tendencies, and parents can adapt their behaviors based on the response and need of the child that is indicated in the birthchart. If we can't adapt our behavior to prevent poor responses, astrology is a waste of time.
You can look at the assumed birth chart of Adolf Hitler and there is nothing in the chart that indicates mass murder. All anyone would likely assume among other facts, is that he is an artist, a persuasive public speaker, who has a need for control, and possibly he has very pronounced fears. Another example of this inability to tell would be Timothy McVeigh. His Pisces Moon trine Neptune doesn't really strike the mind as the kind of thing that would make a person blow down a building even though the negative of Pisces is the tendency to be paranoid and often have delusions in regard to the government; the absences of his mother in his teenage years was certain difficult for him. Looking in hindsight one might suspect that his shyness and sensitivity contributed to his inability to socialize-- which developed into a very serious problem for him that he masked behind an intellectual front (Gemini rising). I don't see how you can tell the difference between a Taurus that is going to blow down a building and one that is just irritatingly stubborn from the natal chart without knowing more about the person. Once you know the circumstances, the behaviors are more explainable, but truthfully much of it is hindsight.
The better question might be how are going to define evil. It is more likely that these people actually are not evil, but that negative behavior is the result of people being extremely mistaken and misguided. Hilter thought that he was beautifying the world. Ignorance looks like evil and it doesn't have any limitations. It seems more likely that people are capable of the most destructive acts simply because there is some extreme lack in their education, and it is going to be hard to pinpoint that on a birthchart.