Perhaps behavior which is less than acceptable begins with boredom. Risky ventures such as infidelity, lying, betrayal of trust, and/or abuse, both mental and physical . . . tend to take over the individual who indulges in them. As if the mind no longer directs, but has been infiltrated and overcome.
It seems really strange to observe a person who leads a double life . . . what could such an existence lend to anyone save trouble? Upheaval, chaos. It may be that those who walk that thin line, teetering on the edge of destruction themselves while placing others in a direct line of fire, have been modified beyond redemption by an energy previously unknown, one which is relentless.
Very often, people who have caused immense damage to others, some too vulnerable to resist, will state that they could not stop what they were doing, as if some unseen force, undeniable, made them commit the acts. A strong, sound mind. When is it possible to know when this is altered -- by the perpetrator, or by observers?
Technological advances we have, and they are many. Progress in identifying criminal insanity before it is unleashed on innocent, unsuspecting others has not kept pace.