During my first job, as a psychologist at a psychiatric hospital, I told my psychoanalyst/supervisor my adolescent patient's statement. "That's psychotic," the doctor replied. Though able to define "psychotic," until that moment I hadn't grasped the power of this condition.
Similarly, when the latest horrors become public, the perpetrators are usually viewed with surprise since they look so normal, lacking the twisted features of horror film characters and speaking coherently though of bogus beliefs. Columnists then ask the usual question of "why," and provide their usual answer that "no one knows" but this is not true. While predicting violence cannot be certain, it correlates highly with several factors: failure in life; substance abuse; the psychological (ego) capacities governing thinking and behavior being inadequately developed; and having a fragmented "sense of self" (sense of who they are).
The killer's frequent decision, to suicide in "glory," is considered preferable to their continued painful existence.Though their act is horrendous, these individuals are not often considered "insane" which is a legal term determined by state statute. Most usually whether a person can distinguish "right" from "wrong" and, contrary to popular belief, rarely succeeds as a defense.
But to describe these individuals as sane does not imply that they possessed normal control over their behavior. Still, except for those possessing extreme psychological limitations, this should not influence their punishment. There is evil in the world and some succumb to its temptation. Yet even for others, the unconscious is very powerful and one must respect its power.