Is there a connection between illegal immigrants and crime?

A large majority of the areas recorded decreases in both violent and property crime between 2007 and 2016, consistent with a quarter-century decline in crime across the United States. The analysis found that crime went down at similar rates regardless of whether the undocumented population rose or fell. Areas with more unauthorized migration appeared to have larger drops in crime, although the difference was small and uncertain…

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).