Are the Deadliest Mass Shootings Preventable? An Assessment of Leakage, Information Reported to Law Enforcement, and Firearms Acquisition Prior to Attacks in the United States

Published date01 August 2019
Date01 August 2019
Subject MatterArticles
Journal of Contemporary Criminal Justice
2019, Vol. 35(3) 315 –341
© The Author(s) 2019
Article reuse guidelines:
DOI: 10.1177/1043986219840231
Are the Deadliest Mass
Shootings Preventable?
An Assessment of Leakage,
Information Reported to Law
Enforcement, and Firearms
Acquisition Prior to Attacks in
the United States
Adam Lankford1, Krista Grace Adkins1,
and Eric Madfis2
This study examined the 15 deadliest public mass shootings in the United States
from March 1998 to February 2018 to assess (a) leakage of violent thoughts/intent,
(b) leakage of specific interest in mass killing, (c) concerning behaviors reported to
law enforcement, (d) concerning interest in homicide reported to law enforcement,
and (e) firearms acquisition. We then compared our findings on the deadliest public
mass shooters with the Federal Bureau of Investigation’s (FBI) 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 that 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.
1The University of Alabama, Tuscaloosa, AL, USA
2University of Washington Tacoma, WA, USA
Corresponding Author:
Adam Lankford, Department of Criminology & Criminal Justice, The University of Alabama, P.O. Box
870320, Tuscaloosa, AL 35487-0320, USA.
840231CCJXXX10.1177/1043986219840231Journal of Contemporary Criminal JusticeLankford et al.
316 Journal of Contemporary Criminal Justice 35(3)
public mass shootings, warning signs, prevention, leakage, firearms
Despite decades of research into the psychology, behavior, and life histories of mass
shooters, many people remain skeptical that it will ever be possible to predict or pre-
vent their attacks. For instance, recent media articles have insisted that “We Can’t
Predict Who Will Commit a Mass Shooting” and that “Predicting a Mass Shooting Is
Impossible” (Resnick & Zarracina, 2018; Singal, 2015).
The phrase “mass shooting” is often used to refer to a more specific type of crime
known as a public mass shooting or an active shooting. These are incidents in which
perpetrators open fire in public places with the intent of harming multiple victims, and
do not include gang conflicts, robberies, or other more conventional crimes (Blair &
Schweit, 2014; Lankford, 2016b). The key distinction is that while public mass shoot-
ings are traditionally defined as cases resulting in four or more victims being killed,
active shootings have no minimum threshold (Blair & Schweit, 2014; Fox & Levin,
2015b; Lankford, 2016b). Past attacks have occurred at schools and colleges, work-
places, malls, movie theaters, churches, government buildings, military facilities, and
other public locations (Blair & Schweit, 2014; Kelly, 2012).
Part of the prediction and prevention challenge is that even in the United States—
where these offenders are most common—there are more than 1 million people who
will not commit a public mass shooting for every individual who does (Blair &
Schweit, 2014; Kelly, 2012; Lankford, 2016b). This makes preemptively identifying
possible offenders seem as hopeless as finding the proverbial needle in a haystack.
Even if the search for potential mass shooters is narrowed to subsets of the population
most likely to contain at-risk individuals, this is not nearly precise enough for success-
ful risk assessment. For example, most public mass shooters are male, but the vast
majority of men and boys would never consider committing a mass shooting (Madfis,
2014c). Similarly, most public mass shooters own guns and struggle with mental
health problems, but the vast majority of gun owners and people with mental illness
are also nonviolent (Madfis, 2014b; Schildkraut & Muschert, 2013; Schug & Fradella,
Leakage of Mass Shooters’ Violent Thoughts and Intent
Fortunately, the challenge is not necessarily to identify public mass shooters among
millions of law-abiding citizens, because in many cases they actually identify them-
selves. This is often referred to as “leakage.” As O’Toole (2000) summarized in her
threat assessment of school shooters, “‘Leakage’ occurs when a student intentionally
or unintentionally reveals clues to feelings, thoughts, fantasies, attitudes, or intentions
that may signal an impending violent act. These clues could take the form of subtle
threats, boasts, innuendos, predictions, or ultimatums” (p. 16).

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