While mass shootings are considered statistically rare, they have become deadlier over time. One way to mitigate the severity of a mass shooting is to exploit the continuum that exists in each element of the Routine Activity Theory (RAT). Using data from the Violence Project mass shooter database, this study tests the relationship between all three components of RAT and mass shooting fatalities. Results reveal that, after controlling for other the components, offender motivation and target suitability significantly predict an event’s severity. Specifically, the number of firearms to brought to a scene and the location’s openness and density are positively related to event fatalities. These findings offer practical policy implications that can mitigate the severity of future mass shootings.