What is a Mass Shooting? What can be done?

Richard Berk

On Saturday night, June 4th, 15 people were shot while enjoying a night out on the 200 block of South Street in Philadelphia. Restaurants, bars, and entertainment venues had drawn large crowds when a fight broke out, and shots were fired. Eleven people were wounded. Three were killed. Because of the large number of revelers and an earlier incident, many police officers already had been patrolling near by. As the shooting began, some bystanders drew their handguns. It is not clear whether they fired any shots. No arrests were made at the scene, but within a week, four individuals identified on security cameras were arrested and charged. Was this a mass shooting? How might it have been prevented?
 
In the United States, there are several different, but common, definitions of mass shootings. The Congressional Research Service defines mass shootings, as multiple, firearm, homicide incidents, involving 4 or more victims at one or more locations close to one another. The FBI definition is essentially the same. Often there is a distinction made between private and public mass shootings (e.g., a school, place of worship, or a business establishment). Mass shootings undertaken by foreign terrorists are not included, no matter how many people die or where the shooting occurs.
 
These formulations are certainly workable, but the threshold of 4 or more deaths is arbitrary. There are also important exclusions. For example, if 10 people are shot but only 2 die, the incident is not a mass shooting. Homicides by other means also are not counted. If 5 people are purposely run down and killed by an individual driving motor vehicle, the deaths do not count because a firearm was not involved. There also are inclusions that can seem curious because the motives of perpetrators are not considered when defining a mass shooting.
 
For example, multiple homicides that result from an armed robbery gone bad are included. So are multiple homicides that result from turf wars between rival drug gangs. The heterogeneous nature of more stereotypic mass shootings needs to be unpacked as well. There are important differences between mass shootings in schools, places of worship, business establishments, outdoor rock concerts, private residences, and other settings. At the very least, there is reason to suspect that each is characterized by different kinds of motives.
 
The South Street incident would not be counted as a mass shooting by most official definitions because fewer than four individuals were killed. A shooting incident in a Buffalo supermarket two days earlier, in which 10 people died, counts as a mass shooting. Differences in how mass shootings are defined make it difficult to arrive at agreement about the number of victims each year or which kinds of incidents are more common. A very rough estimate is that over the past decade, there have been about 40 deaths per year. Virtually all perpetrators were male (just as in most violent crime). Mass shootings associated with intimate partner violence apparently were the most common type.  An estranged husband, for instance, kills his wife, their children, and perhaps her parents. There also is some indication that the number of mass shooting deaths has been increasing over time. The increase seems to result from greater lethality per incident, not a greater frequency of mass shootings. The easy availability of semi-automatic firearms may be an explanation. But any such claims depend on how mass shootings are defined, and different claims can result from different mass shooting definitions. Sloppy media coverage adds to the confusion.
 
What might be done about mass shootings? A lot depends on the particular setting and circumstances, as well as the motives and weapons perpetrators bring to the scene. By these criteria, the South Street and Buffalo incidents were very different. In Philadelphia, there were four male shooters, apparently armed with semi-automatic handguns, who drew and fired their weapons largely on impulse. The shooters were Black, but the crowd into which they fired was diverse. Ideology seemed to play no role. There were police officers patrolling close by, and many in the crowed were armed.
 
In Buffalo, there was a White, 18 year old, single shooter dressed in tactical gear, armed with a semi-automatic assault rifle, and carrying a camera to stream the carnage. His attack was premeditated. He was determined to shoot Blacks. An armed, private security guard at the market was killed, but evidently none of the shoppers were seen carrying handguns.
 
Some claim that mass shooting perpetrators suffer from severe forms of mental illness. Perhaps the Philadelphia and Buffalo shooters qualify. Then, better mental health services might have helped. However, many shooters do not survive the shooting incident, and there is often very little earlier information about their mental health. In addition, the vast majority of people who need of mental health services pose no threat of violence, let alone of committing a mass shooting. We have, therefore, no evidence one way or the other that mental illness is at the heart of most mass shootings. But even if mental illness were a key factor, prospective mass shooters would need to already have been receiving mental health services for their hostile intentions to be identified. In the past, at least, most mass shooting perpetrators were not receiving such services. Perhaps the most promising setting for mental health interventions is high schools, where regular contact with counselors could be made universal. However, there are a host of cost and privacy complications, and a very large number of false positives is a likely result.
 
Others claim that the problem is easy access to firearms, especially semi-automatic handguns and assault rifles. The United States, just like all countries, has a large number of individuals who for many reasons are prone to violence. Lethality from semi-automatic firearms can turn a brawl into firearm deaths, much as it did in Philadelphia. The 2nd amendment, coupled with the sheer number of semi-automatic weapons throughout the country, make gun control options very challenging. There are, for example, important design flaws in background checks that fail to cover private transactions or sales at gun shows. But, even well-designed and implemented background checks only can work if prospective mass shooters have disqualifying attributes that are recorded and retrievable. One important instance may be perpetrators of intimate partner violence who are under a court order prohibiting possession of a firearm. Currently, there are proposals to close loopholes for partners who are only dating. Other suggestions more broadly include barring individuals under 21 years of age from purchasing semi-automatic firearms and requiring more extensive background checks on under-age purchasers. There are also proposals to repeal liability protections for firearm dealers and manufacturers covering guns and ammunition.
 
Outright banning of all military style assault weapons has achieved little traction over the past couple of decades. More surgical interventions, such as banning high capacity magazines probably has greater political viability. Gun purchase waiting periods and limiting individuals to no more than one gun purchase a month have been proposed for years. Some people favor a one-size-fits-all intervention; “a good guy with a gun will stop a bad guy with gun.” There is no credible scientific evidence to support this view, as the Philadelphia and Buffalo incidents illustrate.
 
Still others claim that “target hardening” is the answer. For institutions such as high schools, target hardening in principle might help. But that means determining exactly what target hardening entails and what works, both informed by real evidence, not by sales pitches from security firms or fact-free ideological assertions. There are also major challenges in scaling up to the approximately 20,000 high schools in the United States, the vast majority of which will not experience, and are not in danger of ever experiencing, a mass shooting. High school students are far more likely to die in a fatal, automobile accidents than to be killed in a school mass shooting. For other venues, such as business establishments, shopping centers, outdoor concerts and private residences, the challenges are greater.
 
There is yet another possibility. Mass shooters often need to prepare. They may require at least one, and often more than one, semi-automatic firearm and many rounds of ammunition. Some obtain bullet-resistant vests. There also has been a tendency to broadcast motives, intentions, and even exact targets on social media. These indicators often materialize shortly before a mass shooting is undertaken and can, in principle, can be monitored.  “Red Flag’’ laws would then allow authorities to confiscate temporarily all of an individual’s firearms. For example, a victim of intimate partner violence may be able to alert police or providers of domestic violence support services that her husband/boyfriend has credibly threatened fatal violence. Various kinds of surveillance might then be undertaken, assuming that criminal justice agencies (i.e., police, prosecutors, courts) properly follow through, as a precursor to invoking a red flag intervention.
 
The importance of well-executed gun policy cannot be overstated. The will and resources must be there. Too often they are not. Many promising gun policies fail because they are not faithfully implemented. A common example is a failure to confiscate firearms when required. Another common example is a failure to record important information that might anticipate a shooting. 
 
Each homicide is a tragedy, and deaths from mass shootings should be understood within the broader context of gun violence in the United States. According to the local NBC station in Philadelphia (https://www.nbcphiladelphia.com/news/local/a-record-murders-in-philly-in-2021-scrapes-scars-into-the-citys-psyche/3093658/), there were 599 homicides in Philadelphia in 2021, the vast majority of which were deaths from firearms. Also in 2021, over 200 Philadelphia children of school age or younger were shot while not in school. Most survived, but the number of shootings for that year exceeded the number of mass school shooting victims across the entire country, including those who survived their wounds.  Philadelphia is not an outlier.
 
 
 

References

 
William J Krouse and Daniel J. Richardson (2015) Mass Murder with Firearms: Incidents and Victims. 1999—2013. Congressional Research Service (https://fas.org/sgp/crs/misc/R44126.pdf)
Cynthia Lum and Christopher S. Koper (2020), Countering Mass Violence in the United States. Special issue of Criminology and Public Policy,  free access (https://onlinelibrary.wiley.com/toc/17459133/19/1)
Rosanna Smart (2018) Mass Shootings: Definitions and Trends.” In Gun Policy in America, Andrew Morral, Santa Monica, CA Rand Corporation (https://www.rand.org/research/gun- policy.html)
 
 
Appendix: From the National Academy of Medicine
 
 
Evidence on high-capacity magazine bans
1. Study evaluating the effect of large-capacity magazine (LCM) bans on the frequency and lethality of high-fatality mass shootings in the United States from 1990-2017: Klarevas, L., Conner, A., & Hemenway, D. (2019).The effect of large-capacity magazine bans on high-fatality mass shootings, 1990–2017American Journal of Public Health109(12), 1754-1761.
 
2. Study examining the relationship between bans of LCMs and purchaser licensing laws on incidence of mass shootings from 1984-2017: Webster, D. W., McCourt, A. D., Crifasi, C. K., Booty, M. D., & Stuart, E. A. (2020).Evidence concerning the regulation of firearms design, sale, and carrying on fatal mass shootings in the United StatesCriminology & Public Policy19(1), 171-212.
 
3. Study evaluating changes in mass shooting deaths during the 10-year period when large-capacity magazines and automatic and semiautomatic weapons were illegal: DiMaggio, C., Avraham, J., Berry, C., Bukur, M., Feldman, J., Klein, M., ... & Frangos, S. (2019).Changes in US mass shooting deaths associated with the 1994–2004 federal assault weapons ban: Analysis of open-source dataJournal of Trauma and Acute Care Surgery86(1), 11-19.
 
4. Study on the use, impacts, and regulation of assault weapons and other high-capacity semiautomatic firearms as they pertain to the problem of mass shootings in the United States: Koper, C.S. (2020). Assessing the potential to reduce deaths and injuries from mass shootings through restrictions on assault weapons and other high‐capacity semiautomatic firearmsCriminology & Public Policy, 19(1), pp.147-170. 
 
 
Evidence on domestic violence restraining orders precluding firearm possession
1. Longitudinal study examining the impact of laws that (a) prevent individuals subject to a current restraining order from owning or purchasing a firearm, (b) those that prevent individuals who have been convicted of domestic violence misdemeanors from owning or purchasing a firearm, and (c) those that permit law enforcement officials to seize firearms when at an alleged domestic violence scene on rates of female intimate partner homicide rates: Vigdor, E. R., & Mercy, J. A. (2006).Do laws restricting access to firearms by domestic violence offenders prevent intimate partner homicide?Evaluation Review30(3), 313-346.
 
2. Study on domestic violence restraining orders gun restrictions and violent crimes:  Zeoli AM, McCourt A, Buggs S, Frattaroli S, Lilley D, Webster DW. (2018) Analysis of the Strength of Legal Firearms Restrictions for Perpetrators of Domestic Violence and Their Associations With Intimate Partner Homicide. American Journal Epidemiology. Nov 1;187(11):2365-2371. doi: 10.1093/aje/kwy174. PMID: 30383263.
 
 
Evidence on gun storage and child access laws
1. Study examining the impacts of child access prevention laws on rates of unintentional deaths of children under age 15 across all 50 states and DC from 1979 to 1997: Webster, D. W., & Starnes, M. (2000).Reexamining the association between child access prevention gun laws and unintentional shooting deaths of childrenPediatrics106(6), 1466-1469.
 
2. Study examining the relationship between laws establishing a minimum age for purchasing firearms and child access prevention laws on rates of suicide among youth ages 14-20 between 1976 and 2001  Webster, D. W., Vernick, J. S., Zeoli, A. M., & Manganello, J. A. (2004).Association between youth-focused firearm laws and youth suicides. JAMA292(5), 594-601.
 
3. Study examining the relationship between four different kinds of handgun laws (waiting periods, universal background checks, gun locks, and open carrying regulations) and suicide rates in 2013: Anestis, M. D., & Anestis, J. C. (2015).Suicide rates and state laws regulating access and exposure to handgunsAmerican Journal of Public Health105(10), 2049-2058.
 
 
Evidence on universal background checks
1. Study examining the relationship between four different kinds of handgun laws (waiting periods, universal background checks, gun locks, and open carrying regulations) and suicide rates in 2013: Anestis, M. D., & Anestis, J. C. (2015).Suicide rates and state laws regulating access and exposure to handgunsAmerican Journal of Public Health105(10), 2049-2058.
 
2. Study examining the relationship between purchaser licensing laws and background check requirements on homicide and suicide rates in four states from 1985 to 2017: McCourt, A. D., Crifasi, C. K., Stuart, E. A., Vernick, J. S., Kagawa, R. M., Wintemute, G. J., & Webster, D. W. (2020).Purchaser licensing, point-of-sale background check laws, and firearm homicide and suicide in 4 US states, 1985–2017American Journal of Public Health110(10), 1546-1552.
 
 
Evidence on licensing
1. Study examining the relationship between purchaser licensing laws and bans of large-capacity magazines on incidence of mass shootings from 1984-2017: Webster, D. W., McCourt, A. D., Crifasi, C. K., Booty, M. D., & Stuart, E. A. (2020).Evidence concerning the regulation of firearms design, sale, and carrying on fatal mass shootings in the United StatesCriminology & Public Policy19(1), 171-212.
 
2. Study examining the relationship between purchaser licensing laws and background check requirements on homicide and suicide rates in four states from 1985 to 2017: McCourt, A. D., Crifasi, C. K., Stuart, E. A., Vernick, J. S., Kagawa, R. M., Wintemute, G. J., & Webster, D. W. (2020).Purchaser licensing, point-of-sale background check laws, and firearm homicide and suicide in 4 US states, 1985–2017American Journal of Public Health110(10), 1546-1552.
 
3. Study examining the impacts of the enactment of a “permit-to-purchase” (PTP) law in Connecticut and the repeal of a PTP law in Missouri on suicide rates from 1981-2012: Crifasi, C. K., Meyers, J. S., Vernick, J. S., & Webster, D. W. (2015).Effects of changes in permit-to-purchase handgun laws in Connecticut and Missouri on suicide ratesPreventive Medicine79, 43-49.
 
4. Study examining the impact of Missouri's 2007 repeal of its PTP handgun law on states' homicide rates, controlling for changes in poverty, unemployment, crime, incarceration, policing levels, and other policies that could potentially affect homicides: Webster, D., Crifasi, C. K., & Vernick, J. S. (2014).Effects of the repeal of Missouri’s handgun purchaser licensing law on homicidesJournal of Urban Health91(2), 293-302.
 
5. Study evaluating the effect of Connecticut's enactment of a PTP law in October 1995 on subsequent homicides: Rudolph, K. E., Stuart, E. A., Vernick, J. S., & Webster, D. W. (2015).Association between Connecticut’s permit-to-purchase handgun law and homicidesAmerican Journal of Public Health105(8), e49-e54.
 
6. Summary of the evidence on handgun purchaser licensing on gun violence: Crifasi, C.K., McCourt, A. D., Webster, D. W. (2022). Impact of Handgun Purchaser Licensing on Fun ViolenceWhite Paper, Johns Hopkins Bloomberg School of Public Health
 
 
For general scope of gun violence in the US
1. Goldstick, J.E., Cunningham, R.M. and Carter, P.M. (2022). Current causes of death in children and adolescents in the United StatesNew England Journal of Medicine, 386(20), pp.1955-1956.
 
2. Wintemute, G.J. (2015). The epidemiology of firearm violence in the twenty-first century United StatesAnnual Review of Public Health, 36, pp.5-19.
 
3. Naghavi, M., Marczak, L.B., Kutz, M., Shackelford, K.A., Arora, M., Miller-Petrie, M., Aichour, M.T.E., Akseer, N., Al-Raddadi, R.M., Alam, K. and Alghnam, S.A.. (2018). Global mortality from firearms, 1990-2016JAMA, 320(8), pp.792-814.
 
4. Branas, C.C., Nance, M.L., Elliott, M.R., Richmond, T.S. and Schwab, C.W. (2004). Urban–rural shifts in intentional firearm death: different causes, same resultsAmerican Journal of Public Health, 94(10), pp.1750-1755. 
 
5. Rivara, F.P., Studdert, D.M. and Wintemute, G.J. (2018). Firearm-related mortality: a global public health problemJAMA, 320(8), pp.764-765.
 
6. Alcorn, T. (2017). Trends in research publications about gun violence in the United States, 1960 to 2014JAMA Internal Medicine, 177(1), pp.124-126.
 
7. Centers for Disease Control and Prevention. (2022). Firearm Deaths Grow, Disparities Widen. May 2022 Vital Signs. 
 
8. Kegler SR, Simon TR, Zwald ML, et al. (2022). Vital Signs: Changes in Firearm Homicide and Suicide Rates — United States, 2019–2020. MMWR Morb Mortal Wkly Rep 2022;71:656–663.
 
 To access pdf versions of all the articles above, please use this folder: https://drive.google.com/drive/folders/1aiK5Og1v6dmzSl1RLfYqp71iNFMy_uhN?usp=sharing
 
 
(revised and expanded on June 13, 2022)
Richard Berk
Emeritus Professor of Criminology and Statistics
University of Pennsylvania