Using FBI homicide data for 1976-94, the study assessed patterns in 456 incidents of mass murder in the United States and compared them with cases claiming fewer lives. Overall, the study found that the mass murderer tends to be a white male adult who methodically kills family members or other victims he knows well with a gun or rifle; by contrast, the single-victim murderer tends to be a young black male who is more likely to kill during an argument. A typology is also advanced in which motivations for mass murder are interpreted typically as revenge against particular individuals, against a particular category of individuals, or against society in general. In addition to revenge, other motivations include, love, profit, and terror. The study identified six factors that can be used to explain the often deliberate actions of the mass murderer. These are long-term frustration, externalization of blame, catastrophic loss, external cues, isolation, and access to weapons of mass destruction. The authors advise, however, that none of these factors, either individually or in combination, is sufficient to produce mass homicide. Empirical research is needed to test, refine, or refute components of the model. 7 tables and 20 references