The record on "active shooter" fatalities is fragmented; as a result, the AMA researchers who published Lethality of Civilian Active Shooter Incidents With and Without Semiautomatic Rifles in the United States in JAMA (Sci-Hub Mirror) had to piece together their own data from disparate sources.
The researchers concluded that access to semiautomatic rifles significantly increased the deadliness of mass shootings, nearly doubling the average number of fatalities and increasing nonfatal injuries by a wide margin. The researcher point out that this finding reflects the semiautomatic rifles "working as intended": "Semiautomatic rifles are designed for easy use, can accept large magazines, and fire high-velocity bullets, enabling active shooters to wound and kill more people per incident."
The researchers studied lone shooters (excluding the San Bernadino killers) and also excluded the 2017 Mirage shooting in Las Vegas, which was an outlier in terms of fatalities. They tallied 248 shootings, between 2000 and 2017.
Their conclusions: semiautomatic rifles boost fatalities by 94% and injuries by 81% on average.
The researchers lamented that they could not learn more from these shootings given the limitations of the FBI data. For instance, details about the injuries sustained by victims might help them pinpoint how much additional danger — if any — a semiautomatic weapon presents.
They also speculated that the intentions of shooters who wield semiautomatic firearms might be different from those of other shooters. If so, that difference might account for at least some of the additional injuries and deaths.
“This lack of data highlights the need for a national centralized database to inform the debate on an assault weapons ban,” the researchers wrote.
Lethality of Civilian Active Shooter Incidents With and Without Semiautomatic Rifles in the United States [Elzerie de Jager, Eric Goralnick, Justin C. McCarty, et al/JAMA] (Sci-Hub Mirror)
Shooters are twice as deadly when a semiautomatic rifle is in the mix, study finds [Karen Kaplan/LA Times]