Terrorists, street gangs, lone sociopaths, sociopaths in groups and pledged to a utopian vision killed people they did not know, against whom they had no realistic complaint, for the purpose of attracting attention, making a statement, intimidation, or even just for the thrill of it.
Criminals, including terrorists, street gangs, and lone psychopaths, targeted unknown individuals without a reason to complain, in order to draw attention, make a point, frighten people, or experience excitement.