That's probably true, but I am willing to bet they have zero evidence of that at this point in the investigation. Sounds to me like buying him the gun was all they needed to charge him with murder.
Also I disagree completely with A) calling it an assault weapon. You don't need to do that, that's what we have liberals for and B) a blanket statement that you shouldn't buy one for a 12 year old. It's just a gun right ? Just a semi automatic rifle like any other. I owned a couple when I was that age.
I want to know how the kid got the gun and took it to school though. I mean I could have probably pretty easily snuck out of the house with one of my guns at that age I guess. You know, if I wanted my dad to kick the ever loving dog **** out of me, but.....