That's the first I've heard that his parents warned police to "check him out." This dude was nothing more than a ticking time bomb that finally went off.
Therapy since 8 is what led to this behavior. You can’t possibly have a kid grow up healthy when the therapy culture is all about self esteem and learning victimhood. The kid should have been in church groups, boy scouts, and playing sports. The things boys are suppose to do. Nope, the kid lived a sheltered life in an office where he learned how the world revolves around himself and pumped full of drugs. Ultimately he is responsible for pulling the trigger and stabbing his victims. But since the people always want to blame something for these catastrophes I lay the blame on his parents and the lifestyle they lived.