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The mass murderer is known by a variety of names in both public and academic spheres, from the family annihilator to the active shooter, from the workplace avenger to the rampage school shooter. Although most researchers acknowledge that the phenomenon is heterogeneous, mass killing has defied classification, and currently no consensus typology exists. Most previous efforts at developing a classification scheme have focused on sorting these multicides into three broad groups, namely, family, felony, and public mass killings, exclusively relying on qualitative methods and case-study analysis to do so. The present study employs a multivariate approach to examine differences among types in victim, offender, and incident characteristics on the population of all mass murders in the United States from 2006 to 2016.

In this study, we analyzed the relationship between state firearm laws and the incidence and severity (i.e., number of victims) of mass public shootings in the United States during the period 1976 -2018. Hypotheses: We hypothesized that states requiring permits to purchase firearms would have a lower incidence of mass public shootings than states not requiring permits. We also hypothesized that states banning large-capacity ammunition magazines would experience a lower number of victims in mass public shootings that did occur than states without bans. Method: We developed a panel of annual, state-specific data on firearm laws and mass public shooting events and victim counts. We used a generalized estimating equations logistic regression to examine the relationship between eight state firearm laws and the likelihood of a mass public shooting. We then used a zero-inflated negative binomial model to assess the relationship between these laws and the number of fatalities and nonfatal injuries in these incidents. Results: State laws requiring a permit to purchase a firearm were associated with 60% lower odds of a mass public shooting occurring (95% confidence interval [CI: Ϫ32%, Ϫ76%]). Large-capacity magazine bans were associated with 38% fewer fatalities (95% CI [Ϫ12%, Ϫ57%]) and 77% fewer nonfatal injuries (95% CI [Ϫ43%, Ϫ91%]) when a mass shooting occurred. Conclusion: Laws requiring permits to purchase a gun are associated with a lower incidence of mass public shootings, and bans on large capacity magazines are associated with fewer fatalities and nonfatal injuries when such events do occur. Public Significance StatementWe cannot definitively conclude that implementing a specific law would lead to a change in the incidence or severity of mass public shootings. However, laws that limit potential shooters' access to firearms by requiring permits may reduce the incidence of mass shootings, and laws that limit the number of shots that can be fired before reloading may reduce the severity of mass public shootings when they do occur. Such laws must be balanced with citizens' right to bear arms under the Second Amendment of the U.S. Constitution.

Homicide followed by suicide remains an understudied phenomenon in the criminological literature. This is due, in part, to methodological and statistical limitations—much of the extant research includes small samples and has not kept pace with quantitative advances. Moreover, scholarship on homicide–suicide has been focused almost exclusively on individual risk factors, discounting contextual influences. In this study, we examine whether macro‐environmental characteristics affect the odds of suicide after a homicide. We use data on 24,373 homicide and homicide–suicide cases distributed across 3,019 cities and 48 U.S. states from the National Violent Death Reporting System to examine the direct effects of structural factors on the odds of suicide after a homicide; and whether structural characteristics condition the impact of the victim–offender relationship on the odds of homicide–suicide. Hierarchical logistic regression models indicate that macro‐level concentrated disadvantage decreases the odds of homicide–suicide. Furthermore, concentrated disadvantage attenuates the odds of suicide after the homicide of an intimate partner, child, family member, or friend, relative to the killing of a stranger. The findings reveal that researchers should account for the context in which homicide–suicide occurs; failure to do so may unintentionally discount a key correlate of homicide–suicide and artificially inflate the effects of the micro‐environment.

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