12 cases in which armed civilians stopped mass shootings (October 2015) This Washington Post article cites 12 cases in which armed civilians (not police officers) either stopped or prevented mass shootings with their own concealed carry firearm. Source: https://www.washingtonpost.com/news/volokh-conspiracy/wp/2015/10/03/do-civilians-with-guns-ever-stop-mass-shootings/