By nine a lot of kids would have experienced a death in the family, or somewhere in their wider social circle. None of the kids I grew up around were as naive and innocent by that age.
We don't have the necessary information to answer that. Like I said if he accidentally shot her your argument would have more merit, although the blame would still fall on the idiot parents.
But it wasn't an accident from what we know, he meant to kill her. If there's no gun maybe he stabs her or bludgeons her to death. A lot of people are acting like there was no way that would have happened, but any way you slice it committing a murder as a nine year old is a sign of severe mental illness.
I think it's odd that you have people shooting each other, bombing each other, running down crowds in vehicles, and in each case people want to focus on the method instead of the motivation. That just doesn't make sense.