A research literature in both criminology and economics suggests that, at a minimum, immigration is not an important determinant of crime in the United States.   However, the literature remains unsatisfying in several ways.  First, the available literature rarely disaggregates the effects of immigration on crime by nationality. In particular, there is little research that addresses the criminal participation of recent Mexican immigrants.  As Mexican immigrants comprise over one third of all immigrants to the United States and over half of all undocumented immigrants, assessing the effect of Mexican immigration on crime would appear to be particularly relevant. Second, prior literature has not been able to disaggregate between crimes committed by immigrants and crimes committed against immigrants.  This is particularly concerning both because immigrants may be less likely than natives to report being victimized and because immigrants may be especially attractive crime victims.  Finally, estimates of the effect of immigration on crime available in prior literature can only be given a causal interpretation under stringent assumptions regarding the inability of immigrants to adjust the timing and destination of migration in response to conditions in U.S. cities. To the extent that migrants select into U.S. cities on the basis of city-specific characteristics, standard regression estimates will return an inconsistent estimate of the effect of immigration on crime.

In this study, I leverage a natural experiment created by recent legislation in Arizona to estimate the impact on crime of an extremely large and discrete decline in the state's foreign-born Mexican population. I show that Arizona's foreign-born Mexican population decreased by as much as 20 percent in the wake of the state's 2008 implementation of the Legal Arizona Workers Act (LAWA), a broad-based "E-Verify" law requiring employers to verify the immigration status of new employees, coupled with severe sanctions for employer noncompliance. By contrast, the law appears to have had no effect on the state's share of other foreign-born individuals or U.S.-born Hispanics. In order to isolate the causal effect of the passage and implementation of LAWA on crime, I leverage a synthetic “differences-in-differences" estimator, using a new method of counterfactual estimation proposed by Abadie, Diamond and Hainmuller (2010). To provide a direct estimate of the effect of Arizona's Mexican immigrant share on its crime rate, I extend the synthetic differences-in-differences framework to construct implied synthetic instrumental variables estimates, using LAWA as an instrument for a state's Mexican population share. In contrast to previous literature, I find significant and large effects of Mexican immigration on Arizona's property crime rate. Results are likely driven, in part, by the fact that LAWA resulted in especially large declines among Mexican migrants who are young and male and, as such, the effects are partially compositional.

The remainder of the paper considers how to interpret these estimates. In particular, I present a theoretical model of immigrant offending and characterize analytically the conditions under which an empirical estimate of the immigrant share on the reported crime rate will be a conservative estimate.