Examining differences between mass, multiple, and single-victim homicides to inform prevention: findings from the National Violent Death Reporting System

Abstract

Background: Multi-victim homicides are a persistent public health problem confronting the United States. Previous research shows that homicide rates in the U.S. are approximately seven times higher than those of other high-income countries, driven by firearm homicide rates that are 25 times higher; 31% of public mass shootings in the world also occur in the U.S.. The purpose of this analysis is to examine the characteristics of mass, multiple, and single homicides to help identify prevention points that may lead to a reduction in different types of homicides.

Methods: We used all available years (2003-2017) and U.S. states/jurisdictions (35 states, the District of Columbia, and Puerto Rico) included in CDC's National Violent Death Reporting System (NVDRS), a public health surveillance system which combines death certificate, coroner/medical examiner, and law enforcement reports into victim- and incident-level data on violent deaths. NVDRS includes up to 600 standard variables per incident; further information on types of mental illness among suspected perpetrators and incident resolution was qualitatively coded from case narratives. Data regarding number of persons nonfatally shot within incidents were cross-validated when possible with several other resources, including government reports and the Gun Violence Archive. Mass homicides (4+ victims), multiple homicides (2-3 victims) and single homicides were analyzed to assess group differences using Chi-square tests with Bonferroni-corrected post-hoc comparisons.

Results: Mass homicides more often had female, child, and non-Hispanic white victims than other homicide types. Compared with victims of other homicide types, victims of mass homicides were more often killed by strangers or someone else they did not know well, or by family members. More than a third were related to intimate partner violence. Approximately one-third of mass homicide perpetrators had suicidal thoughts/behaviors noted in the time leading up to the incident. Multi-victim homicides were more often perpetrated with semi-automatic firearms than single homicides. When accounting for nonfatally shot victims, over 4 times as many incidents could have resulted in mass homicide.

Conclusions: These findings underscore the important interconnections among multiple forms of violence. Primary prevention strategies addressing shared risk and protective factors are key to reducing these incidents.

Keywords: Family violence; Firearm violence; Homicide; Injury; Intimate partner violence; Mass homicide; Mass shootings; Suicide; Surveillance; Violence perpetration; Violence prevention.

Fig. 1

Distribution of the number of victims in mass homicide incidents (N = 141), National Violent Death Reporting System, 2003–2017*. * All 50 U.S. states, the District of Columbia and Puerto Rico are currently funded to participate in NVDRS, but at the time of this study several of the newer states/jurisdictions had not yet completed a data collection cycle and therefore are not included. States and jurisdictions were first funded to participate in NVDRS in different years. Data for this study comes from the following 37 states/jurisdictions: Maryland, Massachusetts, New Jersey, Oregon, South Carolina, and Virginia (2003–2017); Alaska, Colorado, Georgia, North Carolina, Oklahoma, Rhode Island, and Wisconsin (2004–2017); Kentucky, New Mexico, and Utah (2005–2017); Ohio (2010–2017); Michigan (2014–2017); Arizona, Connecticut, Illinois, Indiana, Iowa, Kansas, Maine, Minnesota, New Hampshire, New York, Pennsylvania, Vermont, and Washington (2015–2017); Hawaii (2015–2016); California, Delaware, West Virginia, the District of Columbia, and Puerto Rico (2017). Illinois, Pennsylvania, and Washington collected data on ≥80% of violent deaths in their state, in accordance with requirements under which these states were funded. Data for California are for violent deaths that occurred in four counties (Los Angeles, Sacramento, Shasta, and Siskiyou). **Number above bar represents the number of incidents with the number of victims indicated in corresponding column on x-axis (e.g., N = 96 out of the total of 141 mass homicide incidents had 4 victims)

Fig. 2

Firearm type* used in single, multiple, and mass homicides, National Violent Death Reporting System, 2003–2017**. *Data presented in this figure reflect firearm homicide incidents where the firearm(s) used had a known “action” type (semi- or fully automatic vs. not semi- or fully automatic) within firearm type (31% single homicides; 51% multiple homicides; 56% mass homicides). The remaining percentage with a known firearm type (handgun vs. long gun) had an “unknown” or “other” action. Across homicide types, an average of 53% of NVDRS incidents have a known firearm type. ** All 50 U.S. states, the District of Columbia and Puerto Rico are currently funded to participate in NVDRS, but at the time of this study several of the newer states/jurisdictions had not yet completed a data collection cycle and therefore are not included. States and jurisdictions were first funded to participate in NVDRS in different years. Data for this study comes from the following 37 states/jurisdictions: Maryland, Massachusetts, New Jersey, Oregon, South Carolina, and Virginia (2003–2017); Alaska, Colorado, Georgia, North Carolina, Oklahoma, Rhode Island, and Wisconsin (2004–2017); Kentucky, New Mexico, and Utah (2005–2017); Ohio (2010–2017); Michigan (2014–2017); Arizona, Connecticut, Illinois, Indiana, Iowa, Kansas, Maine, Minnesota, New Hampshire, New York, Pennsylvania, Vermont, and Washington (2015–2017); Hawaii (2015–2016); California, Delaware, West Virginia, the District of Columbia, and Puerto Rico (2017). Illinois, Pennsylvania, and Washington collected data on ≥80% of violent deaths in their state, in accordance with requirements under which these states were funded. Data for California are for violent deaths that occurred in four counties (Los Angeles, Sacramento, Shasta, and Siskiyou). ***Most firearms within the category “semi-automatic or automatic” were semi-automatic. Across homicide types, 19% of all long guns within this category were classified as fully automatic (range: 17-21%). One mass homicide incident was categorized as being perpetrated with a fully automatic long gun, which was a semi-automatic firearm modified to fire like an automatic firearm