I thought this article does a nice job summarizing the role of an armed citizen that may find themselves in the midst of an "active killer" situation.
http://concealednation.org/2017/02/armed-citizen-considerations-in-the-time-of-the-active-killer/
http://concealednation.org/2017/02/armed-citizen-considerations-in-the-time-of-the-active-killer/
