Many mass killers have engaged in a number of significant preincident actions related to firearms, such as training at a public gun range or a secret location. Some of the killers had years of experience with firearms training, had obtained firearms illegally, or had some military experience with weapons. Research has shown that individuals at risk for overt violent behavior may have an obsessive interest in violent video games. At least 11 mass murderers since 1996 were reported to have had an excessive interest in violent video games. Regarding equipment acquisitions by mass killers prior to their attacks, these have included the stockpiling of ammunition, equipment to secure doors or distract the police, and material that might be used for a distraction, such as an accelerant for a diversionary arson. Mass killings have also been preceded by the killers committing murder of family members in residential settings before moving to a public location for mass murder in public. This fact emphasizes the importance of a rapid deployment when home-based killings are reported, so as to determine whether family members may be prominent suspects, and if so, their current location and/or a relevant vehicle description. Regarding what is missing from the typical mass murderer’s equipment are body armor and materials for barricades that suggest a long-term defense against a police attack. This is because most mass murderers commit rapid-fire killings over a short term followed by a suicide, either at their own hand or by police.