The psychopath is one of the most fascinating and distressing problems of human experience. For the most part, a psychopath never remains attached to anyone or anything. They live a "predatory" lifestyle. They feel little or no regret, and little or no remorse - except when they are caught. They need relationships, but see people as obstacles to overcome and be eliminated. If not, they see people in terms of how they can be used. They use people for stimulation, to build their self-esteem and they invariably value people in terms of their material value (money, property, etc..).
A psychopath can have high verbal intelligence, but they typically lack "emotional intelligence". They can be expert in manipulating others by playing to their emotions. There is a shallow quality to the emotional aspect of their stories (i.e., how they felt, why they felt that way, or how others may have felt and why). The lack of emotional intelligence is the first good sign you may be dealing with a psychopath. A history of criminal behavior in which they do not seem to learn from their experience, but merely think about ways to not get caught is the second best sign.
The following is a list of items based on the research of Robert Hare, Ph.D. which is derived from the "The Hare Psychopathy Checklist-Revised, .1991, Toronto: Multi-Health Systems." These are the most highly researched and recognized characteristics of psychopathic personality and behavior.