This is a great article written back in 1994, even though it is over 20 years old, it is spot on and gives some great info on key symptoms of psychopathy along with how to protect ourselves and others.  The truth is these type of people are all around us, we may work with one or have one in our social group.  Please read the article it is long but well worth the study.  I also highly recommend books by Gavin DeBecker in order to help you detect and protect against this type of behavior and the dangers it presents in our lives.