Computer games (such as DOOM) allow for the player to create individual scenarios that can reveal the fantasies and cognitive postures of the player. Eric Harris developed computer games that constituted an externalization of his mindset. This article examines six of the "add-on scenarios" developed by Eric Harris for one of his favorite computer games, DOOM, which is a first-person shooter game. This analysis is used to present general principles for conducting an investigation of a suspect who is a computer-games player. These principles can also be used to identify warning signs of suicidal or violent behavior and intervene to prevent it. Initial investigative steps are to determine if the subject is a computer games player, and if so, how much time is spent playing games. The next step is to determine whether the games being played have "add-on scenarios" for the player, since these are devised out of the mindset of the player. The "add-on scenarios," as well as the overall game should then be submitted to a psychologist or other behavioral scientist with specialized skill in analyzing the objective creative expressions of persons to determine the characteristics of their cognitive worlds. 1 table