Unless you mean to say that Ms. Toad's parents taught their son to commit unspeakable acts of violence.
Children are not simply younger versions of their parents. My biological dad was an abusive bastard, which he had learned from his dad. I am not. Because while it would have been easy to treat others like he treated me, I made a choice to not do so. But according to your logic, I must be an abusive bastard because that's how my dad raised me.
It's easy to say that his family failed, because there's no price to do so, you're going along with the mob. You get to look suitably outraged and to show everybody just how serious you are about how bad this shooting was. But you lose the opportunity to learn something from it about the human condition.
You lose sight of the fact that a possibly good family may have lost the son they thought they knew. If they weren't racists, didn't raise their kid to do this, then they have to come to grips with the fact that their kid did turn out like that.
Think about what the family and friends of somebody who commits suicide must feel. Asking themselves what they could have done differently, if they should have picked up the phone, or given that person a hug, or whatever. But life doesn't work that way. You can't always see what's going on in somebody else's head. You can't always discern the path they are going down.
In coming to grips with the fact that my dad was an abusive bastard, my grandmother dying, being kicked out of high school and moving 1000 miles, I went to some crappy places emotionally. If I had crossed the line and either harmed myself or others, my mom would have been beside herself even though only the moving was her fault and that was the least of my emotional problems.