Abstract:
This study examined the 15 deadliest public mass shootings in the United States from
March 1998 to February 2018 to assess (1) leakage of violent thoughts/intent, (2) leakage of
specific interest in mass killing, (3) concerning behaviors reported to law enforcement, (4)
concerning interest in homicide reported to law enforcement, and (5) firearms acquisition. We
then compared our findings on the deadliest public mass shooters to the FBI’s findings on active
shooters in general. Overall, the results suggest that most incidents were indeed preventable
based on information known about offenders in advance, and that the deadliest mass shooters
exhibited more warning signs and were more often reported to law enforcement than other
active shooters. Future prevention efforts should aim to educate, encourage, and pressure the
public to report warning signs to law enforcement; educate and train law enforcement so they
can more effectively investigate potential threats; and limit firearms access for people who
have admitted having homicidal or suicidal thoughts or being interested in committing a mass
shooting. These relatively straightforward steps could significantly reduce the prevalence of
future attacks.
