I will forgive any parent’s denial, especially when it comes out of left field with little to no warning specifically. It is still stupid, but I forgive him.
As a parent myself, I can't think of a worse phone call to receive, other than "your child has been killed" is "your child murdered his classmates."
Many of these shooters grew up in dysfunctional homes but others didn't. Growing up in the shadows of Columbine, I often thought of the parents of the killers, seemingly well-adjusted, intact middle-class homes, what we call "normal" families. They had children to bury as well, children they loved and thought they raised right.