Most active shooters do not just snap.

Here are Ten Things We Need to Know about Active Shooters

The 63 active shooters examined in this study did not appear to be uniform in any way based on demographics alone.
Active shooters take time to plan and prepare for the attack, with 77% of the subjects spending a week or longer planning their attack.
Most active shooters obtained their firearms legally.
Only 25% of active shooters in the study had ever been diagnosed with a mental illness.
Active shooters typically experience multiple stressors in the year before they attack.
Each active shooter displayed 4 to 5 concerning behaviors over time that were observable to others around the shooter, such as the active shooter’s mental health, problematic interpersonal interactions, and leakage of violent intent.
Active shooters under age 18, school peers and teachers were more likely to observe concerning behaviors than family members. For active shooters 18 years old and over, spouses/domestic partners were the most likely to observe concerning behaviors.
When concerning behavior was observed by others, the most common response was to communicate directly to the active shooter (83%) or do nothing (54%). In 41% of the cases, the concerning behavior was reported to law enforcement. Therefore, just because concerning behavior was recognized does not necessarily mean it was reported to law enforcement.
In those cases, the shooter’s primary grievance could be identified. The most common grievances were related to an adverse interpersonal or employment action against the shooter (49%)
In most cases (64%), at least one of the victims was explicitly targeted by the active shooter.

Source: FBI

Authors James Silver, Ph.D., J.D., Worcester State University

Andre Simons, Supervisory Special Agent, Behavioral Analysis Unit, FBI

Sarah Craun, Ph.D., Behavioral Analysis Unit, FBI