Homicides in Mexico and the Expiration of the U.S. Federal Assault Weapons Ban: A Difference-in-Discontinuities Approach

The year following the expiration of the U.S. Assault Weapons Ban (AWB), the homicide rate in Mexico increased for the first time in a decade. A difference-in-discontinuities model and a unique dataset are used to compare discontinuities generated by close mayoral elections on either side of the AWB expiration. The model finds a statistically significant increase in the firearm homicide rate following the expiration of the AWB. This effect is larger closer to the U.S.–Mexico border, is isolated to the timing of the expiration, and there is no evidence of a concurrent increase in non-firearm homicides or other violent crime.