This study examined the firearm acquisition histories of mass and active shooters from California.
First, the authors identified 22 individuals with a record of authorized handgun purchase in California who perpetrated an attack between 1996 and 2018. Using incidence density sampling, mass and active shooters were matched to purchasers and compared using conditional logistic regressions. Second, the authors characterized the firearm transaction patterns of 55 mass and active shooters who perpetrated attacks between 1985 and 2018 and implemented a mixed model to identify factors associated with firearms acquired in close temporal proximity to the attack. Compared to legal handgun purchasers, shooters had more purchases of handguns in the year prior to the attack (OR = 5.58, 95% CI: 2.34, 13.33), greater odds of a history of purchase denials (OR = 23.43, 95% CI: 4.55, 120.59), and fewer years between the last recorded purchase and the end date (OR = 0.79, 95% CI: 0.68, 0.90). Among the broader set of mass and active shooters, mixed model results indicated that the firearms acquired close to the attack were more likely to be long guns, discharged during the attack, purchased out-of-state, and acquired by methods other than through a licensed dealer. Findings are suggestive of pre-attack planning. (Published abstract provided).