From the Introduction: "The Department of Homeland Security's (DHS's) U.S. Immigration and Customs Enforcement (ICE) Enforcement and Removal Operations (ERO) is chiefly responsible for locating removable aliens and ensuring that aliens directed to depart from the United States do so, among other things. In carrying out its mission, ICE relies, in part, on state and local law enforcement agencies throughout the country to assist it with identifying removable aliens. The July 2, 2015, slaying of a woman on a San Francisco pier by a reported unauthorized alien with a criminal and deportation history has reignited debate among lawmakers and critics over immigration enforcement in the interior of the country. More specifically, concerns have intensified over the level of cooperation shown by some state and local law enforcement agencies in notifying ICE when they have an alien in their custody. This case is particularly noteworthy because the law enforcement agency in question reportedly did not honor an immigration detainer issued by ICE. […]This report examines the interplay between the federal government (i.e., ICE) and state and local jurisdictions in enforcing immigration law, with a specific focus on noncitizens who have been convicted of a crime. It explores major programs and federal resources available to state and local law enforcement agencies that cooperate with ICE to enforce immigration law. The report begins by briefly discussing the evolution of the cooperation between the federal government and local law enforcement in carrying out federal immigration policy. It then discusses current administrative efforts to involve state and local law enforcement in enforcing immigration law. A brief discussion of resources dedicated to these programs follows. The report concludes with a discussion of select issues and an analysis of possible policy approaches for Congress."
CRS Report for Congress, R44118
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html