I just don't think you can put all parents of murdered children into one category. I have seen parents when a child dies. Sometimes they mourn and rage, sometimes they become catatonic and sometimes even though they are sad they turn to faith and seem strong. Some just shut down and start focusing on crazy things not to think about it.
I think that the death of a child is unique no matter how many times it happens across the globe but until it happens to you, You have no possible idea how you would react.
Among the parents of murdered children there is a commonality.
They all carry the horror on their face. There is no other circumstance - natural death or accident - that creates that look.
That's why Susan Smith wasn't convincing when she said anything about her children. Or Darlie Routier, Diane Downs, Robin Rowe, Frances Newton, etc.