IT'S DEM GAMES I TELL YA, DEM GAMES! Cuz obviously it's not a question of why a kid that age is playing games like that one. And even though I played a GTA when I was 10, and I've yet to kill anyone, the document says "OBSESSED", and obession means pretty much mental disorder.
Also, why was there a gun? Why was he just able to take it from wherever it was? Why does it say "caregiver"? Does that mean there's a background of some sort of why he doesn't live with his parents? May that refer to a worse case of what I previously mentioned? Because while games won't make a person go nuts, easily-impressed people shouldn't be exposed to that, and while I played lots of this games when I was younger, I never presented any case of mental instability, and knew that games are just games a long time before that.
Sometimes, I just fail to see how these people that accuse games right away, seem to lack any kind of critical thinking or common sense, which really does make the latter seem like a super power nowadays.