There’s nothing terribly difficult about this. Spree killers are sociopaths or psychopaths, every time. Both are problems with the brain itself on a physical or chemical level. This is all pretty well known stuff. Sorry you didn’t bother to find out what you were talking about first.
But, Dr. Discostu, that's false. Spree killers can include the depressed/angry, not necessarily with psychopathy. You're BSing with someone who knows better, but I'm amused by your presuming to know the breadth of my knowledge as I am your pretending to know the shooter's mental health status without having examined him, or reading a qualified assessment. You apparently have no idea how silly that is.