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New Studies on Mass Shootings Assess Trends, Gauge Effectiveness, and Offer Policy Recommendations

In the last decade, thousands have been killed or injured as a result of mass violence in the United States. Such acts take many forms, including family massacres, terrorist attacks, shootings, and gang violence. Yet it is indiscriminate mass public shootings, often directed at strangers, that has generated the most public alarm.

Now, 41 scholars have contributed 16 articles on the topic to a special issue of Criminology & Public Policy (CPP), the flagship policy journal of the American Society of Criminology. The articles assess trends in mass violence and gauge the effectiveness of measures to prevent instances of mass shootings and reduce their lethality. The issue also includes research-based policy recommendations to limit the harm from such violence.

“There are no easy solutions or quick fixes for these horrific events,” according to Daniel Nagin, who co-organized the special issue with Christopher Koper and Cynthia Lum, Chief Editors of CPP. “However, there are measures we can take to limit the harm and damage caused by these violent incidents, as well as prevent some shootings from ever taking place. Most of these recommendations require legislative action at the federal and state levels.”

New findings from the studies include:

  • Public mass shootings in the U.S. have become more common and deadly in the last decade: More public mass shooters are motivated to kill large numbers for fame or attention, and experts recommend that the media limit their coverage of shooters to discourage copycats.
  • Mental illness plays less of a role in violence than assumed: Policies that assume serious mental illness causes mass shootings do little to prevent them and subject millions of nonviolent people with mental illness to stigma and unwarranted social control.
  • Threat assessments can help prevent violence: Threat assessments using multidisciplinary teams of law enforcement, legal, and mental health experts have been used successfully in schools and recommended for other environments as a feasible prevention strategy. Yet they have not been adopted nationwide, and social awareness campaigns are needed to encourage reluctant bystanders and family members to report suspicious behaviors.
  • Gun laws can reduce mass shootings: Mass shootings committed with high capacity semiautomatic firearms result in substantially more deaths and injuries than do attacks with other firearms. States with restrictions on large capacity ammunition magazines have fewer mass shooting deaths, as do states requiring firearm purchasers to be licensed through a background check process.
  • Gun violence restraining orders, or “red flag” laws, provide a way to temporarily disarm high-risk individuals: Preliminary research in California suggests that other efforts to identify and disarm high-risk and illegal gun owners may also hold promise.
  • Restrictions on gun owners involved in domestic violence may prevent access to firearms for some potential mass shooters: Restrictions can help only if they are obtained through criminal convictions or restraining orders, and only if the firearm restrictions are actually enforced.
  • Situational crime-prevention strategies should be tested to see if they can prevent public mass violence: Settings can be identified that are at risk of being attacked, leading to more interventions to prevent such attacks or mitigate their harm.
  • Enhanced response to mass shootings can reduce death and disability: By taking a series of evidence-based steps, hospitals, emergency medical teams, police, and the public can lessen the chances that individuals who are injured will be disabled or die.
  • More research and effort are needed: The special issue also addresses using machine learning techniques to identify potential mass shooters, using the Internet and social media to study preventing and responding to mass violence, and the need to develop more comprehensive data systems for studying mass violence.

Based on these and other findings in this special issue, Nagin, Koper, and Lum offer the following policy recommendations:

  1. Staunch the growth of high-capacity firearms.
  2. Curtail access to firearms for dangerous individuals by strengthening background checks for gun buyers, and by instituting extreme risk protection orders, stronger restrictions for domestic violence offenders, and other measures.
  3. Improve threat-detection systems through more widespread use of threat-assessment teams, public education campaigns, and social media analysis.
  4. Expand training, education, and awareness for first responders, trauma centers, and the public on tactics and strategies that can reduce fatalities when an event occurs.
  5. Launch a federally supported effort to formally track mass casualty incidents to support in-depth research and evaluation.


Summarized from the February 2020 special issue on mass violence of Criminology & Public Policy, which came from an April 11-12, 2019, workshop organized by the authors and funded by the National Science Foundation’s Law and Social Science Program. Copyright 2020 The American Society of Criminology. All rights reserved.

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