Personally I think it's more complex than that, but it's only my opinion. When a child (in adulthood or not) is enmeshed with a parent one way to describe it is that there is nothing separating them - it feels physical, as if the child is an extension of the parent's body. Inside the same skin. If the parent is hurt the child feels hurt. I speak from my own experience, and it's not something I was even aware of until I had therapy, because it started so young. It just feels like a need to protect the parent from harm, maybe the other parent (B) who harms them, the parent (A) isn't capable, and the consequences of not doing so are going to cause the death of the parent. Very dramatic and irrational but it is viewed from a child's perspective. Strangely and maybe even perversely in this case it is a rescuing dynamic. I do think that CW was enmeshed with his dad and I do think Shanann's fall out with the Watts and RW's reaction by blocking them all had a very big effect on him. I think he may have really hated Shanann for the perceived injury to his father.
This collided with his finding of a new support person in NK. Without the nut incident I think CW would have manipulated Shanann eventually into leaving him, and he would have lied to everyone that he met NK after Shanann left him. So I think it wouldn't necessarily have ended up in murder.
The other dynamic to this is I think he really hated his mother and was able to project that hatred onto Shanann. I think he compartmentalized the children as objects that were part of Shanann. Possibly.
It's still a work in progress for me. I also haven't factored in the making of the sociopath yet because that is the unknown quantity for me. Top of my wishlist for Christmas is a book called Talking with Psychopaths and Savages!