Note, in the documentary "I, Psychopath" http://youtu.be/jKvhKI6Kxew they run tests in the MRI to predict psychopathy as the inability to consider future consequences on present choices. Thus, in view of this, lack of empathy is not the determining factor in psychopathy, it is lack of foresight. (perhaps it was about being oblivious to future pain - can't quite recall)
Interesting, I recently watched a show that showed that psychopaths are just as able to predict consequences, just like everyone else, but they just don't care if it negatively affects other people. Not because they're actively bad but because they have no empathic impulse.
Also it showed that they demonstrate no emotional response to words such as 'rape'. If you could monitor everyone's brain who just read that word in an MRI, you would be able to see mental activity that is associated with negative emotions. Everyone except psychopaths.
