Mass murders committed with firearms—particularly those incidents that occur in workplaces, schools, restaurants, houses of worship, and other public spaces—cause people to feel anxious and vulnerable, as the recent Charleston, SC, and Chattanooga, TN, tragedies demonstrate. Several such mass murders in 2012, seven incidents by most counts, compounded a fear among many people that "this could happen to me." This rash of shootings prompted media outlets, gun control advocacy groups, and law enforcement agencies to question whether such incidents were becoming more prevalent and deadly, or had possibly reached "epidemic" proportions. Toward those ends, some of these groups amassed compilations of multiple victim homicides, but their methodologies often differed substantially, and their focus and findings were sometimes quite different. A handful of researchers who have studied mass murder have utilized official crime data to compile comprehensive datasets of multiple victim homicides and mass murders. The analysis in this report builds upon the latter work and scholarship, as well as the compilations described above. What is "mass murder" with firearms? According to the Federal Bureau of Investigation (FBI) criminal profilers, the term "mass murder" has been defined generally as a multiple homicide incident in which four or more victims are murdered—not including the offender(s)—within one event, and in one or more geographical locations relatively near one another. It follows then that a "mass shooting" could be defined as a multiple homicide incident in which four or more victims are murdered with firearms—not including the offender(s)—within one event, and in one or more locations relatively near one another. Similarly, a "mass public shooting" could be, and has been, defined to mean a multiple homicide incident in which four or more victims are murdered with firearms—not including the offender(s)—within one event, in one or more public locations, such as a workplace, school, restaurant, house of worship, neighborhood, or other public setting. The FBI profilers, notably, did not specifically address whether mass murder involved a single or multiple offenders, although in a majority of cases, mass murders involve a single offender. According to FBI profilers, a "classic mass murder" involves one person operating in one location at one period of time. They also noted "family mass murder" or "familicide" as a distinct form of mass murder. If a murderer (offender) committed suicide, the incident was labeled a murder-suicide. In this report, the definitions of three, overarching mass shooting patterns—mass public shooting, familicide mass shooting, and other felony mass shooting—mirror guidance provided by FBI profilers and other prominent criminologists. Under these definitions, offenders are not counted as victims. Mass shootings typically renew calls for passage of gun control legislation. In response to the 2007 Virginia Tech massacre, for example, Congress passed the NICS Improvement Amendments Act of 2007 ( P.L. 110-180 ), which addressed improving both federal and state electronic recordkeeping on persons ineligible to possess firearms under federal law due to past histories of mental illness or domestic violence. In response to the Newtown, CT, tragedy, the Senate considered gun control proposals, including amendments to P.L. 110-180 , but tabled that legislation when a consensus could not be achieved. In the House, similar proposals were introduced, but they were not considered in committee, nor did they reach the House floor for general debate. Any mass shootings and subsequent calls to amend gun control laws will likely generate requests for comprehensive data on the prevalence and deadliness of these incidents. To these ends, this report provides data and analysis on mass shootings, that is, mass murders committed entirely with firearms, for a 15-year period (1999-2013) and mass public shootings for the 44-year period (1970-2013). These datasets could possibly provide policymakers with additional vantage points from which to evaluate legislative gun control proposals that are often offered in the wake of particularly deadly mass public shootings. In the wake of tragedy in 2012 in Newtown, CT, Congress defined "mass killings" to mean "3 or more killings in a single incident" ( P.L. 112-265 ; January 14, 2013). That definition does not make reference to a weapon. In the 1980s, the FBI established a system to classify multiple murder, mass murder, spree murder, and serial murder. These efforts were led by the FBI Behavioral Science Unit (BSU) and National Center for the Analysis of Violent Crime (NCAVC). Both the BSU and NCAVC began documenting and studying multiple rapists and killers, as part of a wider process to research and analyze violent crime trends. According to several criminologists, some of whom are retired FBI Special Agents previously assigned to the BSU, crimes can be classified by type, style, and victim counts. Homicides, for example, have been traditionally classified by victim counts (or thresholds) as follows: A single homicide is one victim slain in one event. A double homicide is two victims slain, in one event, in one location. A triple homicide is three victims slain, in one event, in one location. A mass murder is four or more victims slain, in one event, in one location. A spree murder is two or more murder victims slain, in one event, in two or more locations, without the offender "cooling-off" emotionally between murders. The event, however, can be of short or long duration. A serial murder is three or more separate homicidal events, with the offender cooling-off emotionally between homicidal events. In the view of FBI criminal profilers, a four-murder victim threshold constituted a "massacre." And, in this report, an offender is not included in the mass shooting victim counts, if he committed suicide, or was killed in a justifiable homicide. In the Crime Classification Manual , FBI criminal profilers discuss two basic mass murder prototypes: "classic mass murder" and "family mass murder." A classic mass murder commonly involves "a mentally disordered individual" whose problems have increased to the point that he acts out against groups of people who are unrelated to him or his problems. The FBI criminal profilers pointed to the 1966 University of Texas, Austin, mass shooting as an example of a classic mass murder. Sometimes, but not always, offenders in mass public shootings, which are discussed in this report, possibly fit this prototype. The FBI criminal profilers noted further that a classic mass murder event could last minutes, hours, or days. In addition, FBI criminal profilers identified family mass murder as a mass murder prototype, in which an offender murders four or more family members in one event and in one location. Similarly, "familicide" is a term used to describe the murder of multiple family members, most commonly the murder of an intimate partner and children. These definitions with four victim thresholds, however, are not without limitations. For example, they do not capture mass murders in which three victims were shot to death, but additional victims were killed by means other than firearms. Nor do such definitions capture murders in which fewer than four victims were shot to death, but several victims were wounded, sometimes seriously. It is also noteworthy that these FBI classifications of multiple homicides—double, triple, mass, spree, and serial—were largely conceptualized to aid law enforcement in investigations through criminal profiling and not for statistical data collection purposes. When the cases of individual offenders are evaluated, there sometimes exists potential for overlap among these classifications, particularly for mass and spree murders, and less so for mass and serial murders. Consequently, for statistical purposes, these classifications are not always mutually exclusive, which in some cases can present difficulties for researchers and can result in different judgments and varying findings with regard to the frequency and deadliness of these incidents. According to one journal article, in 2010 the FBI adopted a revised definition of mass murder , that is, murderous events resulting in at least four deaths normally taking place at one or more geographical locations relatively near on e another . This revised definition indicates that the potential overlap between mass and spree murders is an issue that has been addressed. As demonstrated below, the definitions used in this report of three, overarching mass shooting patterns—mass public shooting, familicide mass shooting, and other felony mass shooting—mirror in part concepts and definitions developed by FBI profilers. Notwithstanding FBI guidance, gun control and rights advocates, media outlets, law enforcement agencies, and academic researchers often adopt quite different definitions of "mass murder," "mass shootings," and "mass public shootings." As a result, their findings often vary. Nevertheless, the four-victim threshold and other elements of the above definitions reflect a synthesis arguably of the most conclusive, academically rigorous research available on "mass murder." That research is discussed immediately below. Despite the public trauma and outcry generated by mass public shootings, there is a dearth of comprehensive, authoritative data on multiple-victim homicide incidents, either committed wholly or partially with firearms. A handful of criminologists, statisticians, sociologists, and other researchers have analyzed the principal source of national homicide statistics that is compiled by the Department of Justice (DOJ) annually, as part of the FBI's Uniform Crime Reports and Supplementary Homicide Reports (UCR-SHR). From their analyses, the following observations and extrapolations can be made: DOJ's Bureau of Justice Statistics (BJS) estimated that there were 987 four or more victim homicide incidents from 1980 to 2011, or an average of 31 per year. However, while the bulk of those incidents were mass murders, it is probable that some of those incidents were serial murders committed over extended time periods, or spree murders that lasted longer than roughly 24 hours.