Yes, this (and me too). It is unfathomable until you have experienced it. The bare faced lies that these people are unashamed of. My ex was totally unembarrassed to be caught out in a lie. He literally didn't care and would just try another tactic. Because to people like them, there is no shame in lies, lies are a tool to get what they want. Therefore, lies are not bad/shameful in their mind.
I view people 'like this' as a lesser developed type of human (seriously!), it is like their brain has not fully developed from animal to human. They are merely interested in fulfilling their needs - the same way an animal is driven instinctiviely to fulfill its needs - 'these' people are driven to fulfill their needs at any cost. And needs usually equal satisfaction and satiation. In CW's case I think that his need was to be with NK. And SW wasn't going to go away quietly and make it easy for him. So, he had to take action. Eventually, he'd have tired of NK too and would have had another need. But he might not have killed her, I think this because the killing wasn't the purpose for him, the killing was the means to the end. And the end was getting his needs fulfilled.
This assessment comes from my own unfortunate experience - so I am very biased so could be totally wrong.