This source list includes a broad range of immigration experts and advocates, from academics and pro-immigrant groups to organizations that seek to limit the numbers of legal and illegal immigrants. The nexus of illegal immigration and local law enforcement has emerged as a political hot topic, with local law enforcers charging that the federal government has ceded its enforcement responsibilities to the locals. Likewise, the broad issue of crime among illegal immigrants also has emerged as a subject of scrutiny. For resources specific to crime, law enforcement and illegal immigration, see the source listings below for the Police Foundation's “Local Police” initiative and Arizona State University's project on Local Policing, Local Communities and Immigration. A number of academics listed below are conducting research on crime and immigration. They include Kristin Butcher, Scott Decker, Daniel Mears, Anne Morrison Piehl, Rubén G. Rumbaut and Robert Sampson.