Once a shooting has commenced, the shooter has the upper hand because he has planned the event and knows what he intends to do. Law enforcement, on the other hand, is largely caught off guard and must respond as quickly as possible to prevent further injuries or loss of life. Experts who profile mass murderers, serial killers, and spree murderers note that profiling this type of individual is problematic because of the large variation in personality types that has been observed, particularly among young killers who are still developing emotionally and psychologically. Experts do agree that most mass murderers are White males who tend to have interpersonal relationship problems. These individuals are likely to blame others for their problems and to view others as deserving of punishment. Mass killers may also be acting out in a way that recaptures or ensures their masculinity in the eyes of others. Some killers experience a precipitating event that triggers the mass murder spree. The article also includes a description of a project to create a standardized forensic tool that can identify individuals likely to carry out mass violence. The project, called the Depravity Scale, is in the process of collecting data and could have a hand in changing the way law enforcement officers work and how criminals are sentenced.