This should be considered in many mass shooting cases: More than one (hidden) shooter hypothesis. https://www.google.com/search?q=This+should+be+considered+in+many+mass+shooting+cases%3A+More+than+one+%28hidden%29+shooter+hypothesis.&rlz=1C1ONGR_enUS1133US1133&oq=This+should+be+considered+in+many+mass+shooting+cases%3A+More+than+one+%28hidden%29+shooter+hypothesis.&gs_lcrp=EgZjaHJvbWUyBggAEEUYOdIBCDE1NzZqMGo3qAIIsAIB8QU7Yk2kypCJXQ&sourceid=chrome&ie=UTF-8