The evidence is mounting: An Arizona law requiring employers to verify legal residency of job applicants is deterring illegal aliens from coming and staying in the state.

“We find that an Arizona law reducing employment opportunities for unauthorized migrants decreased emigration from and increased return migration to Mexican source regions with strong initial ties to Arizona,” concluded researchers from Carnegie Mellon University and the University of Colorado-Boulder.

The study examined the impact of the Legal Arizona Workers Act, which took effect January 2008. It requires employers in Arizona to use E-Verify, the federal online system that verifies a worker’s identity and authorization to work in the U.S.

Analyzing Mexican ID card (matricula consulare) data, researchers found the rate of illegal immigrants returning to Mexico from Arizona nearly quadrupled from 2005 to 2010.

The increases were especially large for Mexican states closest to Arizona. Sonora, for example, saw a 30 percent increase in the number of migrants returning compared to more distant locales.

The study dovetails with other research showing the influx of illegal aliens fell by almost 50 percent in the seven U.S. states with universal E-Verify laws.

Brian Cadena, associate professor of economics at the University of Colorado and co-author of the Arizona study, noted a Congressional Budget Office estimate that E-Verify could be implemented nationwide for $1.3 billion over 10 years. That would be a drop in the bucket compared to the $135 billion that illegal immigration costs the U.S. annually.