What is a ‘mass shooting’ and how do we talk about gun violence?

In a Q&A, criminologist Richard Berk discusses why definitions matter and what role social media and mental illness play in this context.

A person standing at the foot of a set of outdoor stairs, with a brick wall behind and fencing atop the stairs.
Richard Berk, professor of criminology and statistics. (Image: Eric Sucar)

This past weekend, in Dayton, Ohio, and El Paso, Texas, more than 30 people died, and another 50-plus were wounded in two mass shootings that took place less than 24 hours apart. Though some would argue that the frequency of such incidents has increased, it’s hard to say by exactly how much because different law enforcement agencies and the media often define “mass shooting” differently. In a Q&A, Penn criminologist Richard Berk discusses why this matters, what needs to change, and how the most recent tragedies reflect the current conversation about gun violence.

Let’s start with the most basic question: What is a mass shooting? 

In the United States, there are several different, but common, definitions of mass shootings. The Congressional Research Service, for example, defines mass shootings as ‘multiple firearm homicide incidents involving four or more victims at one or more locations close to one another.’ The FBI definition is essentially the same. Often there’s a distinction made between private and public mass shootings, and mass shootings by foreign terrorists are not included, no matter how many people die or where the shooting occurs.

Do you think these definitions make sense?

These formulations are certainly workable, but the threshold of four or more deaths is arbitrary, and some inclusions can seem curious because perpetrator motive often isn’t considered, regardless of whether the incident takes place at a school, house of worship, business, outdoor concert, shopping mall, or private residence. At the very least, there is reason to suspect that each is characterized by different kinds of motives.

There are also important exclusions to ‘mass shooting’ definitions. For example, if 10 people are shot but only two die, the incident is not a mass shooting. Homicides by other means also are not counted, like in a case where an individual purposely runs down and kills five people using his car. The deaths don’t become part of mass shooting totals because a firearm wasn’t involved.

Given the inconsistent definitions, is it possible to calculate how many people die in mass shootings each year? 

It’s difficult to arrive at a consensus, but a very rough estimate is that during the past decade, there have been about 40 deaths per year attributed to mass shootings. Virtually all perpetrators were male—just as in most violent crime—and mass shootings associated with intimate partner violence were the most common type. There also is some indication that the number of mass shooting deaths has been increasing over time, which seems to result from greater lethality per incident, not a greater frequency of mass shootings. Greater use of assault weapons and high-capacity magazines probably figure significantly in the explanation.

Can we talk for a minute about the recent shootings in El Paso and Dayton? 

El Paso was apparently politically motivated by what is loosely called white supremacist ideology. I don’t know the very latest on Dayton, but the fact that the shooter used an assault weapon with high-capacity magazines and wore body armor is suggestive to some analysts.

Some have made the point that these kinds of mass shooting are not ‘lone wolf’ crimes, that there is, at least, a supportive social media network. Think of it this way: It’s as if the perpetrator routinely attended KKK meetings and then, with no direct guidance from the KKK, blew up an African American church. But now the meetings are virtual.

A lot of attention has been quite properly focused on the lethality of assault weapons in these circumstances. These ‘weapons of war’ are now common on the streets of America. They are engineered to kill many people in a hurry; lethality from semi-automatic firearms can turn a brawl into a mass shooting. Once a prospective mass shooter with an assault rifle arrives at the scene, often little can be done to prevent deaths and injuries. In Dayton, we were remarkably fortunate that the police arrived and neutralized the shooter very quickly, apparently in less than a minute. Had it been even two minutes, many more people would likely have been shot.

Do you think that broader gun control legislation is the answer?

The 2nd Amendment, coupled with the sheer number of semi-automatic weapons in the United States, make gun control options very challenging. Even well-designed and implemented background checks only can work if prospective mass shooters have disqualifying attributes. For instance, it’s not clear to me what type of background check screening would flag something like white supremacy. One important instance may be perpetrators convicted of intimate partner violence or those who are under a court order prohibiting possession of a firearm. More surgical interventions such as banning high-capacity magazines may be a better approach in general. In particular, a ban on assault weapons needs serious consideration. However, there is no quick fix. This may need to become America’s new moonshot. 

What do you make of the link often made between mass shooting and mental illness?

Many shooters don’t survive the shooting incident, and there is often little earlier information about their mental health. In addition, the vast majority of people in need of mental health services pose no threat of violence. So, we have 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. Perhaps the most promising venue for mental health interventions is high schools, where regular contact with counselors could be universal.

And where does social media fit in all of this? 

There has been a tendency for mass shooters to broadcast motives, intentions, and even exact targets on social media. These indicators often materialize shortly before a mass shooting and could, in principle, be monitored. But in reality, there are too many posts to monitor them all. There may be technical solutions, but there would likely be legal pushback. Equally important, mass shooters need to prepare. They require at least one, and often more than one, semi-automatic firearm and many rounds of ammunition. Some acquire bullet-resistant vests and even silencers. The transactions that make this possible might be usefully screened. And in the end, it may come back to, ‘If you see something, say something.’

This was adapted and condensed from a piece originally published on the website of the Department of Criminology in the School of Arts and Sciences at the University of Pennsylvania, with additional reporting included. 

Richard Berk is professor of criminology and statistics at the University of Pennsylvania.