	Introduction

Congress has long supported efforts to identify, detain, and remove noncitizens who have been convicted of crimes in the United States. This report discusses four programs operated by the Department of Homeland Security's (DHS) Immigration and Customs Enforcement (ICE) to identify and remove criminal and other removable aliens. The Criminal Alien Program (CAP) is an umbrella program for marshaling the agency's resources to identify and remove criminal and other removable aliens. CAP is guided by the Priority Enforcement Program (PEP ), which represents a set of enforcement priorities that describe which foreign nationals should be removed and in what priority order. PEP also comprises a data sharing infrastructure or "interoperability" between DHS and the Department of Justice that screens for immigration violations when individuals are booked into jails. ICE's §287(g) program allows DHS to delegate certain immigration enforcement functions to specially trained state and local law enforcement officers, under federal supervision. The National Fugitive Operations Program (NFOP) pursues known at-large criminal aliens and fugitive aliens outside of controlled settings (i.e., administrative offices or custodial settings). PEP, its predecessor Secure Communities, and the §287(g) program have all contributed to DHS removing large numbers of aliens in the past decade. Yet, these programs also have been controversial. Because interoperability screens 100% of people passing through law enforcement jurisdictions, critics often charged ICE with removing many people who either committed minor crimes or who had no criminal record apart from unauthorized presence in the United States. Other critics charge that revisions to the set of enforcement priorities through PEP have since contributed to a sizable decline in the number of enforcement actions. The §287(g) program has raised concerns about the role of state and local law enforcement agencies in immigration enforcement. Inconsistent policies and practices among jurisdictions and allegations of racial profiling, among other issues, caused ICE to revise the program in FY2012 and allow certain §287(g) agreements with law enforcement agencies to expire. Since then, immigration enforcement advocates have questioned why ICE has curtailed the program's use. ICE has recently expressed interest in expanding it. For these and other reasons, Congress may be interested in measures of enforcement levels by program, the level of appropriations for different criminal alien programs, and the role of state and local law enforcement agencies in immigration enforcement. As noted above, all three of these subpopulations—criminal aliens, removable criminal aliens, and aggravated felons—comprise an unknown mix of legally present noncitizens and unauthorized aliens. This CRS report presents data on authoritative published measures that quantify one portion of the criminal alien population—the noncitizen population incarcerated in federal and state prisons and local jails. Federal, State, and Local Incarceration Data

 Table 1 presents CRS tabulations of the total year-end U.S. citizen and noncitizen populations in federal and state prisons and local jails publicly reported by the Bureau of Justice Statistics for 2002 through 2013 (the most recent year for which complete data are available). DHS Programs Targeting Criminal Aliens

Using its enforcement priorities to guide immigration enforcement efforts, ICE operates the following programs targeting criminal aliens. Unlike the §287(g) program, which is part of CAP, NFOP is a separate program, although ICE officers working for NFOP access the same DHS databases and other information sources to select criminal aliens targeted for removal. Criminal alien : A noncitizen who has been convicted of a crime in the United States.
Congress has long supported efforts to identify, detain, and remove criminal aliens, defined as noncitizens who have been convicted of crimes in the United States. The apprehension and expeditious removal of criminal aliens has been a statutory priority since 1986, and the Department of Homeland Security (DHS) and one of its predecessor agencies have operated programs targeting criminal aliens since 1988. Investments in DHS's Immigration and Customs Enforcement (ICE) interior enforcement programs since 2004 have increased the number of potentially removable aliens identified within the United States.
Inconsistencies in data quality, collection, and definitions prevent a precise enumeration of total criminal aliens and key subgroups such as criminal aliens convicted of removable offenses and aggravated felonies. It is also not known what portion of these groups consists of legally present noncitizens and unauthorized aliens. Noncitizens incarcerated in federal and state prisons and local jails—a subset of all criminal aliens—totaled 142,463 in 2013 (the most recent year for which complete data are available), with state prisons and local jails each accounting for more incarcerations than federal prisons. Until recently, the proportion of noncitizens incarcerated in U.S. prisons and jails corresponded closely to that of noncitizens in the U.S. population, but unreported incarceration data since 2013 has hindered such comparisons.
To direct immigration enforcement efforts toward the criminal alien population, ICE operates the Criminal Alien Program (CAP), an umbrella program for marshaling agency resources to identify and remove criminal and other removable aliens. CAP is guided by the Priority Enforcement Program (PEP), which represents a set of immigration enforcement priorities that describe which foreign nationals should be removed and in what priority order. PEP also employs "interoperability," which is a data sharing infrastructure between DHS and the Department of Justice that screens individuals for immigration-related violations when they pass through law enforcement jurisdictions. PEP replaced the former Secure Communities, which many jurisdictions with large foreign-born populations had opposed.
ICE also uses the §287(g) program, which allows the agency to delegate certain immigration enforcement functions to specially trained state and local law enforcement officers, under federal supervision. PEP and the §287(g) program both screen for immigration violations as people pass through the criminal justice system.
The National Fugitive Operations Program (NFOP) pursues known at-large criminal aliens and fugitive aliens outside of controlled settings (i.e., administrative offices or custodial settings). NFOP is not part of CAP, although ICE officers in its workforce use the same DHS resources and databases as ICE officers working for CAP.
PEP, its predecessor Secure Communities, and the §287(g) program have all contributed to DHS removing large numbers of aliens in the past decade. Yet, these programs also have been controversial. Because interoperability screens all people passing through law enforcement jurisdictions, critics often charged ICE with removing many people who either committed minor crimes or who had no criminal record apart from unauthorized presence in the United States. Other critics charge that revisions to the set of enforcement priorities through PEP have since contributed to declining numbers of enforcement actions.
The §287(g) program has raised concerns over inconsistent policies and practices among jurisdictions and allegations of racial profiling, among other issues. Such concerns caused ICE to revise the program in FY2012 and allow certain §287(g) agreements with law enforcement agencies to expire. Since then, immigration enforcement advocates have questioned why ICE has curtailed the program's use. ICE has recently expressed interest in expanding it.
For these and other reasons, Congress may be interested in measures of enforcement levels by program, the level of appropriations for different criminal alien programs, and the role of state and local law enforcement agencies in immigration enforcement.