[SS.I 4.0] This document lists nicknames, usernames, quotations, dates, symbols, and other items that may be used by potential attackers to refer to previous killers or incidents of violence. Knowing these references is important for anyone conducting threat assessments. Version 2.0 greatly expands the list, with a new emphasis on references to ideological hate groups and terror organizations. For examples of cases in which shooters used such insider references prior to their attacks, see the companion document “Reading Between the Lines: Recognizing Insider References to School Shootings.”