This article adds to the growth in data-driven analyses seeking to compare samples of violent extremists with other violent populations of interest. While lone-actor terrorists and public mass murderers are frequently treated as distinct offender types, both engage (or attempt to engage) in largely public and highly publicized acts of violence and often use similar weapons. This article investigates the (dis)similarities between both offender types. We use a series of bivariate and multivariate statistical analyses to compare demographic, psychologic and behavioral variables across 71 lone-actor terrorists and 115 public mass murderers. The results show little distinction in sociodemographic profiles, but significant differences in (a) the degree to which they interact with co-ideologues (b) antecedent event behaviors and (c) the degree to which they leak information before the attack. Overall, our data inform the emerging idea that lone-actor terrorists and public mass shooters are not distinct offender types. There is more that unites them than divides them. Although the over-arching focus of our results are on the few variables that distinguish them, the vast majority (80%+), of the 180+ variables showed no significant difference. We discuss implications for threat assessment and management in the context of these results.