Risk Analysis of Mass Shootings Committed by Immigrants and Natives

Sharks are deadlier than Mexican mass shooters

A total of 298 mass shooters were responsible for 1,733 murders and 2,459 people injured in the United States from 1966 through the end of 2024. Over the 59 years studied here, the chance of being murdered by a mass shooter was about 1 in 9.1 million per year, and the annual chance of being injured was about 1 in 6.4 million. The murder victims of mass shooters account for about 0.15 percent of all homicides from 1966 through the end of 2024, but that percentage has risen in recent years. The deadliest year for mass shootings was 2017, when 14 shooters murdered 130 people and injured 959 others, accounting for 0.7 percent of all homicides in that year.

Of those 298 shooters, 255 were native-born and 43 were foreign-born. The chance of being murdered in a mass shooting committed by a native-born American was about 1 in 10.5 million per year, about 6.5 times higher than the chance of being killed by a foreign-born mass shooter, which was about 1 in 68.4 million per year. The annual chance of being injured by a foreign-born mass shooter was about 1 in 94.7 million, and the chance of being injured by a native-born shooter was about 1 in 6.9 million per year. About 14.4 percent of mass shooters were foreign-born, and they were responsible for 13.3 percent of murders, roughly in line with their share of the population, and 6.8 percent of injuries in mass shootings, roughly half their share of the population.

Mass Shootings

Mass shootings are serious crimes that capture public and media attention because they are brutal, often result in many deaths and injuries, and target random individuals unrelated to any other crime. As a result, the victims of mass shootings are more sympathetic than the victims of most other crimes or victims who are exposed to other risks. Mass shootings are fortunately uncommon and comprise only about 0.15 percent of all homicides in the last 59 years, albeit a higher percentage in recent years, when they’ve accounted for 0.22 percent of all homicides since 2020. The following subsection describes how these numbers are calculated.

Definition of a Mass Shooting

This brief defines a mass shooting as an indiscriminate rampage with a firearm in a public place or place of business that results in at least three victims killed by the attacker. This definition excludes shootings stemming from more conventionally motivated crimes that target specific third-party victims, such as armed robbery, gang violence, shootings resulting from an argument between neighbors or partygoers, and murder-suicides in private, but includes terrorist attacks because these are often indiscriminate killings. Cases in which an indiscriminate rampage occurred that was unrelated to the commission of the shooters’ original planned crime—a robbery, for example—are included. Shootings during a fight that erupted in a public location unconnected to preceding events are excluded, such as Vonzell Roundtree fatally shooting his uncle and three others who were fighting in a Philadelphia bar in 2007. However, shooters who went to a public location to kill a specific person or persons and then intentionally committed an indiscriminate massacre are included.

In cases where the mass shooter killed a person or people in a separate location, public or private, immediately before or immediately after an indiscriminate public shooting, the murders in the separate and public locations are combined into a single mass shooting. That rule is followed even if there were fewer than three total deaths in the indiscriminate public shooting. This is often referred to as a spree killing. For instance, in 2006, Herbert Chalmers Jr. of St. Louis killed two people in private and then took a bus to his job, where he murdered two other people and committed suicide, so his mass shooting resulted in four murders. However, killings committed before mass shootings that are separated over a long period of time are not included. For example, Kori Ali Muhammad murdered three people in Fresno in 2017 in a mass shooting and was also convicted of a murder he committed five days earlier. The three murders he committed in the mass shooting are included here; the murder he committed five days earlier is excluded. Deaths and injuries that occurred due to the police response are counted against the shooter.

Shooters who were convicted and then later acquitted are not included. Also not included are shootouts between a criminal suspect and the police in which the police were not responding to a mass shooting. For a single mass shooting committed by two or more shooters, the murders and injuries are split equally among all shooters. If a shooting victim died years later from medical complications caused by the shooting, that victim is counted as a death from the mass shooting. Any injury incurred during the mass shooting, whether by firearms or other means, is included. In cases of data ambiguity, this method errs on the side of including the shooter and the larger number of fatalities or injuries. Mass shootings are not included if the identity of the shooter is unknown. The definition used in this brief sometimes includes mass shootings that are counted by others as spree murders.

As mentioned above, this brief’s definition of a mass shooting is a combination of several definitions from the government and private researchers. The first such definition was created by the Investigative Assistance for Violent Crimes Act of 2012, which allows for the US Attorney General, at the request of law enforcement at an appropriate state or political subdivision, to assist in the investigation of violent acts and shootings in places of public use, the investigation of mass killings, and the investigation of attempted mass killings. The 2012 act defines mass shootings as three or more killings in a single incident.

The FBI defines mass murder as a “multiple homicide incident in which four or more victims are murdered, within one event, and in one or more locations in close geographical proximity.” In their investigation of mass shootings during the 1999–2013 period, the Congressional Research Service (CRS) used the FBI definition as a baseline to define a mass shooting as “a multiple homicide incident in which four or more victims are murdered with firearms, within one event, and in one or more locations in close proximity.”

The Congressional Research Service similarly defines a mass public shooting as occurring when a shooter commits “a multiple homicide incident in which four or more victims are murdered with firearms, within one event, in at least one or more public locations, such as a workplace, school, restaurant, house of worship, neighborhood, or other public setting.” The Violence Prevention Project Research Center uses the CRS definition for their detailed dataset of mass shootings from 1966 to the present. Mother Jones compiled its dataset from 1982 to the present using a similar definition of four or more victims during the 1982–2012 period, then revising the definition to three or more victims from January 2013 to the present.

In addition to a broad definition of mass shootings that is a combination of many other widely accepted definitions, this brief produces a large and expansive dataset of mass shootings, attackers, victims, and other information. Of course, one could define a mass shooting differently and could include any shooting where a gunman shoots more than one person, but such a definition does not capture the arbitrariness that the public rightly perceives as an essential component of a mass shooting. For instance, a robbery during which gunmen shoot three or more victims is a terrible crime, but it doesn’t produce the same response as a gunman shooting many strangers unconnected to the commission of another crime. This definitional problem has bedeviled government agencies and researchers who have reasonable cause to disagree with each other. The definition of mass shootings in this brief is merely one definition and not the only possible one.

Methodology and Data

This brief focuses on mass shootings in the United States during the 59-year period from January 1, 1966, to December 31, 2024. It attempts to identify all individuals who committed mass shootings, separate them into native-born American shooters and foreign-born shooters, identify their countries of origin, include the number of people they murdered and injured, and note the date of the attack. Due to the large number of potential mass shootings under this brief’s definition, there may be others that are not included. Regardless, this brief includes a substantial majority of the mass shootings over the last 59 years. Counting a murder committed by a mass shooter is straightforward and allows ready comparisons over the years and between attacks and attackers. However, injuries are inherently difficult to compare because there is a broad spectrum of severity, from paralysis and brain damage to minor scratches. As a result, the injury statistic is less meaningful than the murder statistic, and readers should interpret it with caution. When two sources disagree on the number of victims, the larger number is used here.

Information on the identities of the mass shooters, their number of victims, and whether they are foreign-born comes from multiple sources. The first is a massive dataset created by the Violence Prevention Project Research Center that includes detailed information on 200 known and 2 unknown mass shooters since 1966.¹⁸ The center also has data on which mass shooters are foreign-born. The second large dataset is “US Mass Shootings, 1982–2024: Data from Mother Jones’ Investigation,” which includes 151 different shootings since 1982. Prior to January 1, 2013, the Mother Jones dataset includes shootings with four or more victims killed by the shooter but from that date forward lowers the count to three or more victims, to comport with the definition of mass shootings included in the Investigative Assistance for Violent Crimes Act of 2012. The third source is the “Mass Killings in America, 2006–Present” dataset compiled by the Associated Press. The fourth dataset is the “Mass Shooting Tracker,” a crowdsourced listing of shootings in the United States. The fifth source is the FBI, which has numerous reports and bulletins on active shooter incidents in the United States going back to 2000, as well as its supplementary homicide reports. The sixth source is the “Active Attack Data Explorer” compiled by the Advanced Law Enforcement Rapid Response Training (ALERRT) Center at Texas State University. The seventh source is the “Explore the Data: US Mass Killings Since 2006” dashboard created by USA Today.

Data on the US population come from the Census Bureau and the American Community Survey. Data on the number of total homicides come from the Centers for Disease Control and Prevention’s WONDER database.

Mass Shooters and Their Victims

The definition of mass shooting used in this paper and applied to existing datasets and other sources has led to the identification of 298 individual mass shooters in the United States from 1966 to the end of 2024 (Table 1). Those 298 shooters murdered 1,733 people and injured 2,459 people over that time. About 86.7 percent of the victims were murdered by native-born mass shooters, and 13.3 percent were murdered by foreign-born mass shooters. Two hundred fifty-five mass shooters were native-born Americans; 43 mass shooters were foreign-born. Approximately 85.6 percent of mass shooters were native-born Americans, and 14.4 percent were foreign-born.

The chance of being murdered in a mass shooting was approximately 1 in 9.1 million per year (Table 2). The chance of being murdered in a mass shooting carried out by a native-born American shooter was about 1 in 10.5 million per year, and the chance of being murdered by a foreign-born mass shooter was about 1 in 68.4 million per year. In other words, the annual chance of being murdered by a native-born mass shooter was about 6.5 times higher than the annual chance of being murdered by a foreign-born mass shooter.

The annual chance of being injured by a mass shooter was about 1 in 6.4 million, while the chance of being injured by a native-born mass shooter was about 1 in 6.9 million per year, and the chance of being injured by a foreign-born mass shooter was about 1 in 94.7 million per year (Table 2). The chance of being murdered or injured in a mass shooting was higher, at 1 in 3.8 million per year overall, 1 in 4.2 million per year from native-born shooters, and 1 in 39.7 million per year from foreign-born shooters.

The deadliest year for mass shootings was 2017, during which 14 shooters murdered 130 people and injured 959 people (Figures 1–2). Two extraordinarily deadly mass shootings that year account for the high number of victims. The first was committed by Stephen Craig Paddock on October 1, 2017, in Las Vegas, where he murdered 60 people and injured 867 in the deadliest mass shooting in this database. The murder victims in Paddock’s case account for 3.5 percent of all people murdered in a mass shooting since 1966 and 35 percent of all injuries. The other was committed by Devin Patrick Kelley, who murdered 26 people and injured 22 in Sutherland Springs, Texas, on November 5, 2017. Kelley’s mass shooting was the fifth-deadliest since 1966.

The 1,733 murders in mass shootings from 1966 through the end of 2024 account for 0.151 percent of the approximately 1,155,683 million homicides during that time period, with 2024’s homicide data estimated as identical to 2023’s (Figure 3). The annual chance of being murdered in the United States during that time was about 1 in 13,602. In other words, there were about 667 people murdered for every single person murdered in a mass shooting in the United States during that period. Native-born mass shooters were responsible for about 0.13 percent of all murders, and foreign-born mass shooters were responsible for about 0.02 percent of all murders.

Table 3 shows the number of mass shooters and victims by the shooter’s country of origin. The United States dominates with 85.6 percent of mass shooters, 86.7 percent of all murder victims, and 93.3 percent of all injuries in mass shootings. Foreign-born mass shooters account for 14.3 percent of mass shooters, 13.3 percent of murder victims, and 6.8 percent of all injuries in mass shootings. Other than the United States, the country of origin for the greatest number of mass shooters was Mexico (9), followed by Hong Kong (5), China (4), and Cuba (3). Mass shooters from the United States had the greatest number (1,503) of murder victims, followed by South Korea (39), Mexico (34), China (20), and Cuba (15). The South Korean number of murder victims is so high because of the April 16, 2017, mass shooting at Virginia Tech committed by Seung-Hui Cho.

As mentioned above, the annual chance of being murdered by a foreign-born mass shooter was about 1 in 68.4 million a year. However, there is substantial variation in deadliness among foreign-born shooters’ countries of origin (Table 4). Excluding the United States, the largest number of foreign-born shooters were from Mexico, which is unsurprising because Mexico is the origin of more immigrants to the United States than any other country. Still, there have been just 9 Mexican-born mass shooters, who have murdered 34 people and injured 15. The annual chance of being murdered by a Mexican mass shooter was about 1 in 462 million per year—about half the chance of being killed by a shark, which was about 1 in 250 million per year during a similar time.

About 14.4 percent of mass shooters were foreign-born, and they were responsible for 13.3 percent of murders and 6.8 percent of injuries in mass shootings. The foreign-born shares of the mass shooters and their murder victims were roughly equal to their share of their population, but they were less likely than native-born Americans to injure people in attacks. Since 2015, the shares of murder victims of and people injured by foreign-born mass shooters were down. Over the last decade, the share of foreign-born shooters was approximately 14.2 percent, but their share of murder victims was down to 11 percent and their share of injuries was 3 percent. The decline in the shares of foreign-born shooters, murder victims, and injuries occurred even as the total number of murder victims was up by 68 percent in the last decade compared to the previous decade (2005–2014).

Conclusion

A total of 298 mass shooters were responsible for 1,733 murders and 2,459 people injured in the United States from 1966 through the end of 2024, according to the definition of a mass shooting in this brief. There may be other mass shootings missed in the analysis of the last 59 years, but the numbers herein account for at least a substantial majority of all mass shootings during that time. The size of the dataset allows analysis of the risk of mass shootings, the identification of the individual shooters by their countries of origin, and classification of mass shooters by deadliness.

During the 1966–2024 period, the chance of being murdered by a mass shooter was about 1 in 9.1 million per year, and the annual chance of being injured was about 1 in 6.4 million. The murder victims of mass shooters account for about 0.15 percent of all homicides during that period, but that chance has risen in recent years, peaking in 2017. Of those 298 mass shooters, 85.6 percent were native-born Americans and 14.4 percent were foreign-born—roughly similar to their shares of the population in recent years. The chance of being murdered in a mass shooting committed by a foreign-born shooter was about 1 in 68.4 million per year, compared to a 1 in 10.5 million chance of being murdered in a mass shooting committed by a native-born American shooter. Foreign-born people are not disproportionately responsible for deaths or injuries caused by mass shootings. Moreover, as heinous as these crimes are, they are relatively rare.

See the full Cato briefing paper here.