Although I have also seen psychopath and sociopath used synonymously, I believe that some differentiate them based on the cause of their state of being. Such a person would say that a psychopath is caused due to neurological properties of the subjects brain, thus they were born the way they are, whereas a sociopath has become the way they are from exposure to their environment. The upper middle class serial killer is likely a psychopath, the poor minority serial killer gang leader is more likely a sociopath, however in practice they share the same characteristics.