Robert D. Hare — Canadian Psychologist

Robert D. Hare, C.M. is a researcher in the field of criminal psychology. He developed the Hare Psychopathy Checklist, used to assess cases of psychopathy. Hare advises the FBI's Child Abduction and Serial Murder Investigative Resources Center and consults for various British and North American prison services... (wikipedia)

Psychopaths view any social exchange as a 'feeding opportunity,' a contest or a test of wills in which there can be only one winner. Their motives are to manipulate and take, ruthlessly and without remorse.
Measurement and categorization are, of course, fundamental to any scientific endeavor, but the implications of being able to identify psychopaths are as much practical as academic. To put it simply, if we can't spot them, we are doomed to be their victims, both as individuals and as a society.
Not all psychopaths are in prison - some are in the boardroom.
People tend to think of psychopaths as criminals. In fact, the majority of psychopaths aren't criminal.
Science cannot progress without reliable and accurate measurement of what it is you are trying to study. The key is measurement, simple as that.