Here's a link to info about the show and the scale explained in some detail. I found it really interesting to hear it explained in such detail. He even interviewed Tommy Lynn Sells about his killings. According to Sells, he feels no remorse and said that if he did, he would likely kill himself. If I killed upwards of 70 people, I might want to hang myself too.
The show also talked about how psychopaths differ from most people like how that can't empathize and sympathize and just feel in general. The researchers did some basic tests and found that in circumstances where normal people would feel anxious or tense, psychopaths would read normally. Another example was how a psychopath would describe being in love as being on par with having great sex which most of us know is definitely not the case.
Part of the reason they don't feel or think the way normal people do is that their brains ware wired to work differently than most other people's. The researchers were trying to figure out what and how in the brain is working differently and causing the lack of emotion.
One other thing that the show talked about was that most psychopaths were pushed over the edge in some way. For one killer, it was the combination of a troubled childhood and watching an adult man perform oral sex on a little boy. Another was having an overly sexual mother who dominated the household and having both his wives be unfaithful to him. Many psychopaths seem to be functional and mostly harmless until they hit a breaking point, whatever that may be.
Cross posted at random_things, randomthought & my journal