Known to the system? Criminal history, pre-attack behaviors, and firearms acquisition among mass public shooters with documented warning behaviors

Prior research has documented that many mass public shooters have prior contact with the criminal justice system and exhibit observable pre-attack warning behaviors, but these patterns are typically reported in aggregate. Using a dataset of 171 mass public shooting incidents in the United States (1999–2024) involving 175 perpetrators with documented pre-attack warning behaviors (e.g., leakage of intent), the present study examines whether perpetrators with and without criminal records differ in demographic characteristics, pre-attack behavioral indicators, and firearm acquisition patterns. Among the 100 perpetrators with known criminal history status, those with criminal records were significantly older and exhibited fewer documented concerning behaviors, with a similar pattern for grievances. Perpetrators without criminal records more frequently obtained firearms through federally licensed dealers, though this difference did not reach conventional significance. These findings suggest that variation in criminal justice contact corresponds to differences in how perpetrators are visible prior to their attacks, with implications for prevention and intervention. Background checks may be more applicable to individuals with disqualifying histories, whereas behavioral indicators may be more informative for those without prior system contact, though neither approach alone fully addresses both.