	Introduction

Congress has a long-standing interest in the criminal alien population and has supported efforts since the late 1980s to identify, detain, and remove these individuals. The Congressional Research Service (CRS) estimates that about 184,000 non-citizens were incarcerated in 2011 ( Table 2 ) and that the total non-citizen correctional population—which represent a subset of all aliens ever convicted of a crime—may be about 572,000 (see " Other Estimates of the Criminal Alien Population " below). The Department of Homeland Security's (DHS) Immigration and Customs Enforcement (ICE) agency operates four key programs to identify and remove criminal aliens and other removable aliens. First, when, if ever, should DHS exercise its "prosecutorial discretion" by not asserting its full enforcement authority? Some Members of Congress have objected to these policies, and some support legislation to limit the exercise of discretion (see " DHS Enforcement Priorities and Discretion "). A second set of questions concerns the role of state and local law enforcement agencies in immigration enforcement. After describing how these programs function and key differences among them, the report reviews their recent appropriations history and enforcement statistics. The final sections of the report describe the controversies surrounding certain programs targeting criminal aliens—particularly the Secure Communities program and the §287(g) program—and legislative issues that may arise as a result. Three groups of criminal aliens can be distinguished. Thus, as Figure 3 illustrates, the noncitizen proportion of the incarcerated population in 2001-2011 mapped closely to the proportion of noncitizens in the U.S. population overall. In 2011, the Government Accountability Office (GAO) estimated the U.S. criminal alien population in federal prisons and criminal alien incarcerations for state prisons and local jails. ICE currently operates four programs wholly or partly focused on criminal aliens (discussed in more detail below): CAP, Secure Communities, the §287(g) program, and the National Fugitive Operations Program (NFOP). The CAP, Secure Communities, and §287(g) programs are "jail enforcement" programs that screen individuals for possible immigration violations and for criminal-related grounds for removal in federal and state prisons and local jails. NFOP is a "task force" program that targets at-large criminal aliens, including fugitive aliens who have not been convicted of a crime (i.e., prior to entering the criminal justice process) and aliens who have been convicted of crimes and subsequently released from prison. By their nature, jail enforcement programs are not highly targeted: they are designed to screen the entire population of people passing through some part of the criminal justice system. The Obama Administration has published a series of memoranda to prioritize certain aliens for removal and to exercise prosecutorial discretion in other cases (see "DHS Enforcement Priorities and Discretion"). Yet ICE and its partner agencies only have the detention bed space and institutional capacity to remove about 400,000 aliens per year. Concerns about State and Local Enforcement

				State and Local Enforcement Programs May Not Focus on Serious Criminals

A number of observers have raised concerns that ICE's enforcement programs, which ostensibly focus on identifying and prosecuting the most dangerous criminal aliens, also detain large numbers of noncriminal aliens and aliens convicted only of minor offenses. Involving State and Local Law Enforcement in Immigration-Related Screening May Harm Community-Police Relations

ICE's three jail enforcement programs interact in different ways with state and local law enforcement agencies, but all of them rely on such agencies, at least indirectly, as points of contact with potentially removable aliens as they are processed through the criminal justice system. Most removable aliens have never been convicted of a criminal offense.
Congress has a long-standing interest in seeing that immigration enforcement agencies identify and deport criminal aliens. The expeditious removal of such aliens has been a statutory priority since 1986, and the Department of Homeland Security (DHS) and its predecessor agency have operated programs targeting criminal aliens since 1988. These programs have grown substantially since FY2005, and deportations of criminal aliens—along with other unauthorized immigrants—have grown proportionally.
Despite the interest in criminal aliens, inconsistencies in data quality, data collection, and definitions make it impossible to precisely enumerate the criminal alien population, defined in this report as all noncitizens ever convicted of a crime. The Congressional Research Service (CRS) estimates the number of noncitizens incarcerated in federal and state prisons and local jails—a subset of all criminal aliens—at 183,830 in 2011 (the most recent year for which complete data are available), with state prisons and local jails each accounting for somewhat more incarcerations than federal prisons. The overall proportion of noncitizens in prisons and jails corresponds closely to the proportion of noncitizens in the total U.S. population.
DHS's U.S. Immigration and Customs Enforcement (ICE) operates four programs designed in part to target criminal aliens: the Criminal Alien Program (CAP), Secure Communities, the §287(g) program, and the National Fugitive Operations Program (NFOP). CAP, Secure Communities, and the §287(g) programs are jail enforcement programs that screen individuals for immigration-related violations as they are being booked into jail and while they are incarcerated; the NFOP is a task force program that target at-large criminal aliens. This report describes how these programs work and identifies their common features and key differences among them.
While consensus exists on the overarching goal of identifying and removing serious criminal aliens, these programs have generated controversy, in part because many of the aliens identified by ICE have never been convicted of a crime, or have been convicted only of minor criminal offenses. Thus, the programs focus attention on questions about when—if ever—DHS should exercise "prosecutorial discretion" by not asserting its full enforcement authority in certain cases. ICE and DHS officials have testified that resource constraints mean that the department can deport only about 400,000 aliens per year—far fewer than the total number of potentially removable aliens identified. Officials have released a series of memoranda describing criteria to prioritize certain aliens for removal, and to consider exercising discretion in other cases. Some Members of Congress have objected to the Obama Administration's exercise of discretion, and some have proposed legislation that effectively would limit such discretion.
A second set of questions concerns the role of state and local law enforcement agencies in immigration enforcement. Supporters of jail enforcement programs, including the Obama Administration, see them as efficient and even-handed ways to identify criminal aliens. The Administration has particularly focused on Secure Communities, which was deployed in every law enforcement jurisdiction in the country in FY2013. Yet some have raised concerns that jail enforcement programs are not narrowly targeted at serious criminal offenders. Critics also argue that involving state and local law enforcement agencies in immigration enforcement may damage police-community relations, may result in racial profiling, and may result in the wrongful detention of people who have not been convicted of criminal offenses and may not be subject to removal. Although ICE and DHS have taken steps to address both sets of questions, they remain topics of legislative interest in the 113th Congress.