Seniors, are sociopaths created from their experiences or are they born that way?

I ask in this section because of your life observations. I was watching Dr. Drew talk about the Casey Anthony trial. The psychologist said there is some physiological basis (such as genetics or brain damage) along with childhood trauma in the making of a sociopath. The one marker in all of them is that they have no empathy. How is it that one child of several can end up a sociopath if they have the same genetic makeup, and similar parenting style?