This study examines completed, attempted, failed, and foiled mass shooting outcomes in the United States (2000–2019). Comparative analyses of these four outcomes determine differences in the offender, motive, gun, target, and resolution. Findings indicate predictors of completed outcomes included open-space targets and offender death. Attempted outcome predictors included older offenders, victim-specific motives, and workplace targets. Failed outcomes were more likely than completed and attempted outcomes to involve school targets, although still less likely than foiled outcomes. Foiled outcome predictors included younger white co-offenders, fame and ideological motives, multiple guns, and school and religious targets. A discussion of findings provides implications for justice officials and scholars seeking potential procedures for mass shooting harm mitigation and prevention.