A genetic cause for violent rampages of the prepare-and-shoot, "I want to be famous" variety? Doesn't exist in nature. If you ARE involved in that kind of bioengineering, can you please let me in on it?
"Was he being bullied at school"? Shit, did he even go to school? They let him out at the age of 18, I don't think anyone would want to go back to high school at that point...
Bottom fucking line: If any of the hellholes in which he spent four fucking years of his life were in any way able to diagnose and treat real mental illness, they would have done so.
There is therapy for this kind of thing, antipsychotics and real cognitive therapy, but apparently they don't bother with things like that at these "private treatment centers". Instead they just hurt him and threw him out the door a timebomb.
Surprise, surprise.