Okay, i've read a lot of the reviews here, and some seem to be forgetting the fundamental point.
Someone said they saw him in a different light? Like he was a person capable of love?
You saw him in the light HE CONVEYED to others. That was the point. It's teaching you to look out for the little things, because some people are so good at hiding who they truly are. All throughout, there were red flags she ignored.
Someone else made a valid point, that the perspective of law enforcement isn't recognised in the cases of these people. And I agree. No one ever stops to consider how it would impact the lives of the ones forced to deal with them.
The ones who were annoyed that the murders weren't shown? Grow up.
It's a true story. Which means the murders stemmed from his psyche. The more you know about their behaviour, the better chance of recognising it in your own life BEFORE a murder occurs, and thus avoiding a horrible death. Analyse the situation from different perspectives, and you gain a greater understanding in to the way these people operate. To better protect yourselves and the people around you.