Anybody looked into the mental condition called "OCD"? That's Obsessive Compulsion Disorder, where the sufferer is under a compulsion to perform senseless acts. We all have it to a certain extent, like having an impulse to shout out something obscene at a church service.
A planeful of pax should never be allowed to be under the complete control of one person. "They're all mine" would occur to the helpless victim of this condition, and there's no way of identifying him or her in the training.
It is a given that there should always be more than one person in the cockpit at all times, otherwise more such events will be inevitable.