Much speculation has been made in the media as to the causes of mass murder in the United States, yet little empirical research exists to verify factors leading to violence. Prior research primarily relies on case study methodologies or small data sets, but none have focused on the underlying issues observed in a comprehensive national sample. Data for the current study include 152 mass murders reported through the FBI’s Supplementary Homicide Reports and USA Today from 2007 to 2011, which were then matched with media reports for each event. The current study shows that mass murders typically occur following a triggering event, are committed by non-strangers, and are rarely committed by persons with mental illnesses. A more realistic image of these incidents is critical, as misperceptions of offenders and case characteristics can improperly shape public policies.