Most types of crime had an almost flat trend line, indicating that changes in undocumented populations had little or no effect on crime in the various metro areas under survey. Murder was the only type of crime that appeared to show a rise, but again the difference was small and uncertain (effectively zero).

...

The results of the analysis resemble those of other studies on the relationship between undocumented immigration and crime. Last year, a report by the Cato Institute, a libertarian think tank, found that unauthorized immigrants in Texas committed fewer crimes than their native-born counterparts. A state-level analysis in Criminology, an academic journal, found that undocumented immigration did not increase violent crime and was in fact associated with slight decreases in it. Another Cato study found that unauthorized immigrants are less likely to be incarcerated.

At the more local level, an analysis by Governing magazine reported that metropolitan areas with more undocumented residents had similar rates of violent crime, and significantly lower rates of property crime, than areas with smaller numbers of such residents in 2014. After controlling for multiple socioeconomic factors, the author of the analysis, Mike Maciag, found that for every 1 percentage point increase in an area's population that was undocumented there were 94 fewer property crimes per 100,000 residents.

More research is underway about the potential effects of undocumented immigration on crime. Robert Adelman, a professor at the University at Buffalo, SUNY, whose group’s research The Marshall Project and The Upshot have previously documented, is leading a team to expand on the Governing analysis. Early results suggest unauthorized immigration has no effect on violent crime, and is associated with lower property crime, the same as Mr. Maciag found.