Congress has long supported efforts to identify, detain, and remove noncitizens who have been convicted of crimes in the United States. More generally, all unauthorized aliens within the United States are potentially subject to removal, and "interior enforcement" (i.e., alien removals originating from within the United States) is a basic element of immigration control. The criminal alien population, to which such enforcement efforts are targeted, is complex. It is defined in broad terms, challenging to quantify, and sufficiently large and diverse in its criminality that priorities have been established or modified to direct law enforcement efforts. 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. This report begins by defining the criminal alien population and quantifying a portion of it with the limited publically available data. Next it presents the most recent ICE enforcement priorities that emerged with the introduction of PEP in November 2014. The report then describes the major ICE immigration enforcement programs that target criminal aliens. The final section discusses selected policy considerations for programs targeting criminal aliens. This includes a discussion of current levels of enforcement and program appropriations, as well as state and local involvement in immigration enforcement. U.S. immigration law identifies certain crimes that make an alien ineligible for admission to the United States and/or subject to removal. Such crimes include crimes of "moral turpitude"; crimes involving controlled substances; certain firearm offenses; and crimes related to espionage, sabotage, and related offenses. Yet the term "criminal alien" is not specifically defined in immigration law or regulation, and people use it to refer to several different types of noncitizen offenders. At the broadest level, a "criminal alien" is any noncitizen who has ever been convicted of a crime in the United States . This report adopts this broad definition unless otherwise noted. (See Appendix A for a glossary of additional related terms.) Criminal aliens can be further distinguished by legal status, which in turn affects removability. Unauthorized aliens have made up roughly half of all U.S. noncitizens in recent years. The unauthorized alien population includes not only persons who entered without inspection or overstayed the terms of their temporary visas but also persons who have what some refer to as a "quasi-legal" status (e.g., temporary protected status, parole, deferred action) that affords them relief from immediate removal. Hence, not all unauthorized aliens living in the United States are subject to removal. Most unauthorized aliens, however, are removable; but few have been convicted of a crime and are classified as criminal aliens (unlawful presence in the United States itself is a civil violation, not a criminal offense). Three groups of criminal aliens can be distinguished. All criminal aliens include both unauthorized aliens, most of whom are potentially removable, and legal aliens who may or may not be removable depending on specific crimes committed. This population contains the set of criminal aliens who are removable on the basis of specific crimes committed. Criminal aliens who have been convicted of removable criminal offenses are subject to removal under the Immigration and Nationality Act (INA) even if they are otherwise legally present. For example, a legal permanent resident (LPR) convicted of cocaine possession is subject to removal, but an LPR convicted of public intoxication is not. This population also includes aggravated felons. Criminal aliens who have been convicted of aggravated felonies are ineligible for most forms of relief from removal and are ineligible to be readmitted to the United States. 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. In addition, criminal aliens can be distinguished by whether they are currently incarcerated in federal and state prisons and local jails. Accordingly, the criminal alien population can include noncitizens convicted of crimes but who are not incarcerated, noncitizens convicted of crimes who are currently incarcerated, and noncitizens who have ever been convicted of crimes in the past, who have served their sentences, and who have been released from prison and reside in the United States. Having defined the criminal alien population, this report next turns to the issue of quantifying its size. This issue is complicated by the lack of data and published estimates on the criminal alien population. CRS is not aware of any authoritative current estimate for the total criminal alien population . DHS has produced its own estimates of the removable criminal alien population , a subgroup of the total criminal alien population. In 2013, ICE published estimates indicating that approximately 900,000 aliens were arrested for crimes every year; that approximately 550,000 criminal aliens convicted of crimes exited law enforcement custody every year; and that 1.9 million removable criminal aliens currently resided in the United States. 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. Incarcerated noncitizens represent a subset of criminal aliens, but given the paucity of data on the criminal alien population, it represents one consistent annual measure that can be compared both across time and relative to the total U.S. incarcerated population. This section presents incarceration data from 2002 through 2013. It then discusses the quality and limitations of publically available data pertaining to the criminal alien population. 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). This population includes an unknown portion of persons who fall into each of the three criminal alien populations discussed above: total criminal aliens, removable criminal aliens, and aggravated felons. This population also includes both persons lawfully present in the United States and unauthorized aliens. Federal prison data come from annual published BJS reports that compile year-end data collected from the Bureau of Prisons (BOP) under the auspices of BJS's National Prisoner Statistics (NPS) program. State prison data also come from annually published BJS reports that compile mid-year and year-end data collected by the NPS program from the correctional departments of all 50 states. Local jail data come from an annual BJS survey, the Annual Survey of Jails , from which it creates national-level estimates of the number of inmates incarcerated in local jails. In addition, it conducts a complete count of the local jail population every five years through its Census of Jails . Together, these two local jail counts provide a consistent annual series of the total number of persons incarcerated in local jails. Table 1 indicates that as of December 31, 2013, a total of 2,308,158 prisoners (U.S. citizens and noncitizens) were incarcerated: 215,866 in federal prisons; 1,361,084 in state prisons; and 731,208 in local jails. The 142,463 noncitizens reported in federal and state prisons and local jails at year-end 2013 represented 6.2% of the total incarcerated population. Noncitizen inmates comprised 23.5% of the total federal prison population, 3.5% of the total state prison population, and 6.0% of the total local jail population in 2013. The large noncitizen proportion in federal prisons occurs for two reasons. First, immigration offenses, which are prosecuted at the federal level, represent a disproportionate share of federal offenses for which convicted individuals can be incarcerated in federal prisons. Second, data on noncitizens incarcerated in federal prisons are tabulated more accurately and completely than data on those incarcerated in state prisons and local jails, because federal data are collected consistently by one administrative unit using a single definition of noncitizen. Conversely, data collected on noncitizen status at the state level varies by state and in some cases is not reported at all, resulting in widespread underreporting of noncitizens. At the local level, such shortcomings are magnified over an even larger number of jail facilities and information collection policies. Between 2002 and 2012, the noncitizen percentage of the incarcerated population (ranging from 6.7% to 7.4% over this period) mapped closely to the noncitizen percentage of the U.S. population overall (ranging from 6.3% to 7.6% over the same period). However, in 2013 several states, including California, did not report their noncitizen incarcerated populations, causing the total state-level noncitizen incarcerated population to be understated for that year, and making it difficult to compare with that of previous years. As a basis for comparison, noncitizens comprised 7.0% of the total U.S. population in 2013. Several obstacles challenge and limit the ability of researchers to accurately enumerate the criminal alien population or compare its criminal activity to other U.S. populations. For example, federal BOP data include information on citizenship status according to a single noncitizen definition. In contrast, state and local criminal justice jurisdictions differ in how they classify noncitizen prisoners, and not all collect such information; this creates substantial inconsistencies in data quality and completeness at the state and local level. No single and consistent national enumeration of prisoners exists in the United States similar to the decennial census or the Current Population Survey—much less one that focuses on subpopulations such as noncitizens. Attempts to quantify the U.S. criminal alien population have relied on estimation techniques, assumptions about the criminal alien proportion of the total criminal population, and federal surveys and censuses of prison inmates. This section discusses several data limitations associated with quantifying the criminal alien population. Incarcerations imperfectly measure criminality, because some people initially incarcerated in local jails—a sizable portion of the total incarcerated population—have not yet been charged or convicted of crimes. Conversely, incarceration data understate the number of convicted criminals because they exclude persons on parole and persons sentenced to probation. For instance, of the 6,899,000 individuals included by BJS in its 2013 count of the total correctional population, 3,910,600 were on probation (56%), 853,200 were on parole (12%), and 2,220,300 were incarcerated in federal and state prisons or local jails (32%). Caution must be exercised when examining incarceration data because changing numbers of incarcerations do not always indicate changes in the level of criminal activity. They may indicate changes in enforcement policy. For instance, a reduction in incarcerations for illegal immigration entry may stem from fewer persons attempting to enter the United States illegally, but it may also reflect changes in resources or enforcement priorities. It is also noteworthy that some crimes are never reported: incarcerations only reflect the number of offenses known to law enforcement. Data availability and reliability represent key obstacles to quantifying the national criminal alien population and its level of criminality. For example, no recent and complete publicly available data exist on two potentially useful indicators—arrests and convictions—at the state and local levels that distinguish between U.S. citizens and noncitizens. Consequently, this report limits its analysis to incarcerations. BJS's state and local incarceration data are based on the voluntary participation of each state's department of corrections and local jails. While all states contribute data to BJS on their prison population, states' definitions vary, posing challenges to estimating the size and character of the criminal alien population. For instance, while some states report noncitizen incarcerations, others report all foreign-born prisoners, including naturalized U.S. citizens, potentially inflating counts of the criminal alien population. Local jail reporting practices are likely to be even more inconsistent than state practices given the far greater number of jurisdictions. And not all local jurisdictions report on their foreign-born criminal populations. For these reasons, the Government Accountability Office (GAO) concluded in 2005 that "there [are] no reliable population ... data on criminal aliens incarcerated in all state prisons and local jails." Because ICE screens 100% of people passing through most law enforcement jurisdictions, it identifies potential removable aliens (including criminal aliens (see Table 2 )). Given the relative size and the range of criminality of potentially removable unauthorized and criminal aliens, ICE's parent agency DHS—like one of its predecessor agencies, the Immigration and Naturalization Service (INS) —has prioritized certain aliens for removal. It has done so by publishing agency memoranda on enforcement priorities and criteria for exercising prosecutorial discretion. The most current enforcement priorities are guided by the President's 2014 Immigration Accountability Executive Action, which is discussed below. On November 20, 2014, the DHS Secretary published a memorandum announcing new department-wide policies for enforcement priorities of unauthorized aliens. These priorities guide immigration enforcement efforts involving alien removals undertaken through the CAP program, the §287(g) program, and NFOP. The memorandum laid out three enforcement priorities and mandated that unless certain circumstances occur, aliens described in Priority 1 ( threats to national security, border security , and public safety ) must be prioritized for removal, those in Priority 2 ( misdemeanants and new immigration violators) should be removed, and those in Priority 3 ( aliens issued final orders of removal on or after January 1, 2014) should generally be removed. These enforcement priorities revised, rescinded, and superseded earlier policies promulgated by former ICE director John Morton in 2011. Among the most substantive changes, an alien who was issued a final order of removal prior to 2014 is no longer an enforcement priority, provided he or she is neither a criminal nor a national security concern. Other changes include increasing the priority level of aliens apprehended at or between ports of entry while attempting to illegally enter the country, and specifying the types of misdemeanor offenses that make an alien a focus for removal. Using its enforcement priorities to guide immigration enforcement efforts, ICE operates the following programs targeting criminal aliens. As noted above, the Criminal Alien Program (CAP) is an umbrella program that marshals ICE agency resources to identify, detain, and remove criminal aliens. CAP is guided by the Priority Enforcement Program (PEP). ICE's §287(g) program allows DHS to enter into partnerships with local law enforcement agencies. As such, the program acts as a force multiplier for ICE that can expand its capabilities. The delegation of such enforcement authority occurs through memoranda of agreements that allow ICE to train and rely upon state and local law enforcement officers to handle certain immigration enforcement functions, under federal supervision. Another program that ICE operates to target criminal aliens, the National Fugitive Operations Program (NFOP) , pursues known at-large criminal aliens and fugitive aliens identified and targeted for removal by ICE. While CAP operates mostly within administrative or controlled custody settings, ICE officers who work for NFOP are generally field-based. The Criminal Alien Program (CAP) is an umbrella program that includes systems for identifying and initiating removal proceedings for priority criminal aliens who are incarcerated within federal, state, and local prisons and jails, as well as at-large criminal aliens who have avoided identification. CAP is intended to prevent the release of criminal aliens from jails and prisons into U.S. communities by securing final orders of removal either prior to the termination of aliens' criminal sentences or subsequently whenever possible, and by taking custody of and removing priority aliens who complete their criminal sentences. Identifying and processing incarcerated criminal aliens before their release from jails and prisons is intended to reduce or eliminate time spent in ICE custody and reduce related overall costs to the federal government. CAP jail enforcement officers screen people to identify and prioritize potentially removable aliens as they are being booked into jails and prisons and while they are serving their sentences. Such screening covers almost all persons booked into federal and state prisons and local jails. CAP officers search biometric and biographic databases to identify matches in DHS databases and interview arrestees and prisoners to identify potentially removable aliens without DHS records. When CAP officers identify a removable alien, they may issue a request for notification to state or local law enforcement agencies formally asking to be contacted prior to an alien's release from custody. Issuance of a request for notification depends on whether removal of the flagged individual accords with CAP priorities. CAP officers may issue an immigration detainer if an individual is subject to a final order of removal. As of April 2016, approximately 1,300 CAP officers were monitoring 100% of federal and state prisons, a total of over 4,300 facilities. This total also includes some local jails but, because of their larger numbers, CAP does not have personnel in local facilities to the extent that it does in the federal and state prisons. In addition to onsite deployment of some ICE officers and agents, CAP uses video teleconference (VTC) equipment that connects jails and prisons to ICE's Detention Enforcement and Processing Offenders by Remote Technology (DEPORT) Center in Chicago, IL. CAP also works with state and local correctional departments that provide inmate roster data which ICE then compares to its immigration databases. CAP manages the Law Enforcement Support Center (LESC) , a 24/7 call-center that conducts database checks on the identity and immigration status of arrestees for ICE officers and law enforcement agencies. CAP also encompasses a number of specialized programs targeting high-priority criminal aliens. For example, CAP's Criminal History Information Sharing (CHIS) allows ICE to negotiate with partner countries for criminal conviction information on foreign nationals who are being repatriated from the United States. The Institutional Hearing and Removal Program (IHRP) coordinates attorneys, immigration judges, and incarcerated aliens to expedite removals by completing removal proceedings prior to the completion of an alien's incarceration. This process reduces or eliminates the need for prolonged immigration detention once inmates enter ICE custody to be removed. Other programs include the Violent Criminal Alien Section (VCAS) for prosecuting recidivist criminal aliens; the Rapid Removal of Eligible Parolees (REPAT) program for facilitating the early release of certain aliens who agree to waive appeals and be removed voluntarily from the United States; and Criminal Alien Program Removal Surge Operations (CAPRSO) for targeting priority criminal aliens who agree to immediate removal. The Priority Enforcement Program (PEP) has two components. First, PEP includes enforcement priorities that guide immigration enforcement. Second, PEP uses interoperability, a biometric information sharing program between DOJ and DHS that screens for potentially removable aliens when individuals are arrested by state and local law enforcement agents. ICE takes enforcement action against individuals unlawfully present or removable due to a criminal conviction in accordance with its immigration enforcement priorities. Individuals prioritized for removal must either be threats to national security, border security, and public safety (Priority 1); misdemeanants and new immigration violators (Priority 2); or aliens issued final orders of removal on or after January 1, 2014 (Priority 3). Under CAP, when law enforcement agencies book (i.e., take custody of) an arrestee and submit the person's fingerprints to the FBI for a criminal background check, the fingerprints also are automatically checked against DHS's Automated Biometric Identification System (IDENT) database. Potential matches are forwarded to the Law Enforcement Support Center (LESC, see "Criminal Alien Program (CAP)"). ICE agents at the LESC confirm the identity of matched fingerprints and screen their records for immigration violations and criminal histories. If the LESC determines that the arrestee may be a removable alien, it notifies one of ICE's Enforcement and Removal Operations (ERO) field offices for the arresting jurisdiction about the match. After being notified that a removable alien has been arrested, the local ERO supervisor reviews the record and decides how to proceed based on the individual's criminal conviction record, DHS enforcement priorities, and the office's available resources (see " DHS Enforcement Priorities and Discretion "). If the office decides to initiate removal proceedings against an alien, it will typically issue a request for notification to be alerted within 48 hours of the individual's release from law enforcement custody. Under some circumstances, ICE may issue an immigration detainer , which requests that state and local law enforcement agencies detain individuals flagged by ICE for removal for 48 hours. Since August 2015, ICE also has been using a Request for Voluntary Transfer for certain cases falling outside of the PEP priority categorization. Priority noncriminal subcategories that are not covered under PEP, but for which ICE may seek transfer from cooperative jurisdictions, are aliens apprehended while attempting to illegally enter the country; unlawfully present aliens who have not resided continuously in the United States since January 1, 2014; aliens who have significantly abused the visa or visa waiver programs; and aliens issued final removal orders on or after January 1, 2014. The §287(g) program is based upon §287(g) of the Immigration and Nationality Act (INA) and permits DHS to delegate certain immigration enforcement functions to state and local law enforcement agencies. Agreements entered pursuant to INA §287(g) (or "§287(g) agreements") enable specially trained state or local officers to perform specific functions related to the investigation, apprehension, or detention of aliens, over a specified period (renewable at ICE's discretion) and under federal supervision. As of January 2016, ICE had §287(g) agreements with 32 law enforcement agencies in 16 states. ICE officials expect that those figures—relatively unchanged since 2013—will increase in 2016. At least 1,675 state and local law enforcement officers had completed ICE's four-week §287(g) training program and had been certified to conduct certain immigration enforcement duties. Prior to 2013, the §287(g) program also encompassed "task force" agreements that allowed deputized local law enforcement officers to question and arrest alleged noncitizens encountered in the field who were suspected of violating immigration laws. ICE allowed all such §287(g) task force agreements to expire by the end of 2012. In 2013, responding to a report by DHS's Office of the Inspector General, ICE revised the §287(g) Memorandum of Agreement to foster clarity and consistency with current ICE policies among state and local law enforcement agencies. Under the current remaining "jail enforcement" agreements, specially trained officers within state and local corrections facilities are authorized to identify criminal aliens by interviewing them and screening their biographic information against the same DHS databases used by CAP agents and officers. Section 287(g) officers also use ICE's database and Enforcement Case Tracking System (ENFORCE) to enter information about aliens in their custody and to generate the paperwork for an immigration detainer and a notice to appear (NTA, initiating the formal removal process). State and local corrections officers are supervised by CAP officers. The National Fugitive Operations Program (NFOP) pursues known at-large criminal aliens and fugitive 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. Unlike CAP, which operates mostly within controlled settings (i.e., administrative offices or custodial settings), ICE officers who work for NFOP apprehend people similar to other field-based law enforcement officers, outside of controlled settings. ICE created NFOP in 2003 to expand the agency's ability to locate, arrest, and remove fugitive aliens. In 2009, with support from Congress, NFOP expanded its focus to include locating, arresting, and removing at-large convicted criminal aliens, aliens who pose a threat to national security and community safety, members of transnational gangs, child sex offenders, and aliens with prior convictions for violent crimes. NFOP also currently prioritizes aliens with removal orders issued on or after January 1, 2014, who have failed to depart the United States. As of April 2016, NFOP consisted of 129 fugitive operations teams covering all 24 ERO field offices. Fugitive operations teams use data from the National Crime Information Center (NCIC) and other intelligence sources and work in partnership with federal, state, local, and international law enforcement partners to pursue criminal aliens and other priority cases. Based on these leads, NFOP teams make arrests and conduct other enforcement actions at worksites, in residential areas, and at other locations. According to ICE, NFOP has helped to reduce the total backlog of fugitive alien cases from 632,726 in FY2006 to about 506,000 in FY2016. However, PEP's revised enforcement priorities have narrowed the scope of NFOP operations. Consequently, many of the non-criminal fugitive aliens present in the United States before November 2014, who made up most of the fugitive alien backlog, are no longer a focus of attention (see " DHS Enforcement Priorities and Discretion "). Criminal aliens now account for an estimated 90% of all fugitive operation arrests. Policy issues for criminal alien programs involve the enforcement levels and costs of the various programs, and the appropriate role of state and local law enforcement agencies in enforcing immigration laws. Table 2 presents data on primary enforcement actions by the four programs discussed in this report from 2004 through 2015, where available. The table presents data on administrative arrests by CAP, Secure Communities, §287(g), and NFOP, as well as data on alien identifications, and removals and returns resulting from PEP/Secure Communities. Data in Table 2 should be interpreted with caution, particularly the interoperability functions of PEP/Secure Communities, which identify potentially removable aliens but are not involved in arrests or placing aliens in removal proceedings. Partly for this reason, the same individual may be counted as an identification, a removal, or an arrest by the different programs in Table 2 . An individual also may be identified or arrested on multiple occasions, causing additional over-counts. In addition, some removable aliens are arrested or placed in removal proceedings outside of these programs, and some aliens are returned or removed in a fiscal year after the year in which they are identified and/or arrested. With these qualifications, the data in Table 2 indicate consistent increases in the number of aliens identified and arrested by these four programs. The data indicate that CAP made over 1.3 million administrative arrests between FY2004 and FY2012, while the §287(g) program and NFOP made about 240,000 and 243,000 administrative arrests, respectively. From FY2009 through the first five months of FY2015, about 47.1 million sets of biometric data were submitted to Secure Communities, resulting in the identification of about 2.4 million matches in the IDENT database (i.e., potentially removable aliens). These identifications led to 324,811 administrative arrests at least through FY2012 and 406,441 aliens removed or returned through the first five months of FY2015. Thus, from FY2009 through the first five months of FY2015, about 5% of all submissions to Secure Communities were identified as potentially removable aliens, and about 17% of people so identified (i.e., about 1% of all submissions) were removed or returned. Funding for immigration enforcement in the U.S. interior has increased substantially since FY2004, the first year in which DHS received dedicated funding for the directorate under which criminal alien programs are located. Table 3 presents funding figures for the CAP, PEP/Secure Communities, §287(g), and NFOP programs. Congress substantially increased funding levels, particularly for CAP and NFOP, from FY2004 through FY2006. In FY2006, appropriators directed ICE to conduct a study of how CAP could be expanded nationwide. In 2008, appropriators expressed concern that ICE was "losing perspective on which aliens represent the most significant threat to the nation's social and economic fabric" and questioned "why a significant number of illegal aliens serving sentences in State and local correctional facilities after conviction for various non-immigration crimes are still released from custody without efforts made to deport those who are deportable." Accordingly, appropriators increased funding for the existing Criminal Alien Program in FY2008; and set aside $200 million in additional funding for a program to "improve and modernize efforts to identify aliens convicted of a crime, sentenced to imprisonment, and who may be deportable, and remove them from the United States once they are judged deportable." ICE applied the additional funding to develop the former Secure Communities. Funding for CAP and Secure Communities increased 58-fold from just $6.6 million in FY2004 to $392.5 million in FY2010 and FY2011 before dropping to $317.2 million in FY2016. Altogether, the four criminal alien programs saw their funding grow from $23.4 million in FY2004 to a high of $690.2 million in FY2010 and FY2011, before declining to $497.7 million in FY2016. The §287(g) and former Secure Communities programs have leveraged state and local law enforcement agencies to identify and detain removable aliens, enhancing ICE's enforcement capacity but also raising concerns about police-community relations and civil rights. Proponents of cooperation between ICE and state and local law enforcement agencies have embraced interoperability and the §287(g) program as powerful tools to combat illegal immigration and associated criminal activity. They argue that it allows a relatively small number of ICE agents to leverage a much larger law enforcement group with closer links to local communities. They cite the efficiency of interoperability and §287(g), which used biographic and biometric records created when individuals are arrested and in law enforcement custody to check for possible immigration violations. They argue that both CAP components allow ICE to place additional immigration enforcement agents directly in state and local jurisdictions as well as identify unauthorized aliens who may have eluded interoperability detection because they entered the United States without inspection. Detractors of such cooperation argue that the programs lack sufficient federal oversight and siphon local law enforcement resources away from preventing and prosecuting local crime. They contend that if the foreign born come to associate state and local law enforcement agencies with immigration enforcement, they will hesitate to report crimes or to cooperate in policing activities. Such behavior is expected especially among those who lack legal status and/or come from countries with weak public trust in law enforcement agencies. They also argue that despite most law enforcement officers' best intentions, state and local law enforcement agency involvement with immigration law enforcement would increase the likelihood that biased officers will engage in racial profiling. They contend that by ensuring all arrestees are screened for immigration violations, jail enforcement programs may incentivize officers to arrest persons suspected of being unauthorized aliens based wholly or partly on racial or ethnic characteristics. Such concerns about the §287(g) program surfaced soon after it was introduced. The program faced criticism because it delegated authority to state and local law enforcement agents over what many considered solely a federal responsibility and allowed such agents to use what was often perceived as undue discretion to shape immigration enforcement decisions. This resulted in different standards for immigration enforcement across jurisdictions, and raised civil liberties concerns. Such criticism prompted reviews by the Government Accountability Office (GAO), the DHS Inspector General (IG), and an independent DHS Task Force. In response, beginning in July 2009, ICE required participating law enforcement agencies to sign revised §287(g) Memorandums of Agreement (MOAs), which increased training requirements and ICE supervision, to continue participating in the program. Other program changes included new record-keeping requirements and other tools to prevent pretextual arrests and racial profiling, new training materials and new detainer forms to further reduce the risk of racial profiling and misuse of these enforcement programs, and the establishment of an Internal Advisory Committee to review and assess ICE field office recommendations on 287(g) applications. Under these new procedures, ICE approved new §287(g) agreements more slowly beginning in 2010 and allowed its §287(g) task force agreements to expire by the end of 2012. Consequently, the total number of §287(g) agreements has diminished from a peak of 64 in 2012 to 32 in 2015. ICE's remaining §287(g) agreements that are currently active are all jail enforcement agreements, for which jail officers' powers under the agreements are limited to custodial settings. In the Secure Communities memorandum of November 20, 2014, the DHS Secretary directed the Office of Civil Rights and Civil Liberties to develop and implement a plan to monitor state and local law enforcement agencies participating in the transfer of foreign nationals to ICE. Some Members have questioned why the agency has reduced its use of §287(g) agreements. According to ICE, resistance to and legal action stemming from both the §287(g) and Secure Communities programs caused the agency to curtail the §287(g) program. Following implementation of the changes and safeguards described above, the agency may consider expanding the program in the future. Others have argued that revisions to the §287(g) program, which include meeting the physical infrastructure requirements under the Prison Rape Elimination Act, and a total of five weeks of required training imposes onerous costs that deter many smaller jurisdictions from participating in the program. Some of ICE's major immigration enforcement programs that target criminal aliens contain components that have been controversial with both immigrant advocacy groups and immigration enforcement advocates. In response, the Obama Administration, like earlier administrations, has modified and revised the program's policies and priorities. Although CAP began three decades ago, it received greater scrutiny in 2008 with the inception of Secure Communities. Immigrant advocates contended the program frequently removed noncitizens who either had committed minor crimes or had no criminal records, and that many of those removed had established family and community ties in the United States, including U.S.-born children. After several years of modifying Secure Communities, the Obama Administration ultimately replaced it with a revised set of priorities under the Priority Enforcement Program. Similarly, the §287(g) program has raised concerns among immigrant advocacy groups about local law enforcement's involvement in immigration enforcement, specifically inconsistent policies, possible racial profiling, and possible damage to community policing through the conflation of immigration enforcement and general law enforcement. In response, the Administration tempered its §287(g) program by revising all Memoranda of Agreements to ensure greater consistency across jurisdictions. In response, however, immigration enforcement advocates have raised questions about why a potentially useful "force multiplier" has been limited rather than expanded. Appendix A. Glossary of Terms Definitions are based on CRS's analysis of statutory definitions where noted and of DHS usage and prevailing definitions in other cases. Absconder : See "fugitive alien." Aggravated felon : A noncitizen who has been convicted of an aggravated felony (see below); aggravated felons are subject to removal from the United States, ineligible for certain forms of immigration relief, and ineligible to be readmitted to the United States. Aggravated felony : A crime identified in §101(a)(43) of the Immigration and Nationality Act (INA), a provision that includes numerous state and federal offenses ranging from murder, rape, and trafficking in controlled substances to theft, bribery, and obstruction of justice. Crimes committed outside the United States may also be considered aggravated felonies if the term of imprisonment was completed within the previous 15 years. At-large criminal alien : A noncitizen who has been convicted of a crime in the United States and is not currently incarcerated. Not all at-large criminal aliens are removable. Civil immigration offense : A violation of federal immigration law under Title 8 of the U.S. Code, the most common being residing in the United States without authorization. A person cannot be sent to prison for a civil immigration offense. They can be penalized by being deported from the United States, which technically is not classified as punishment. Criminal alien : A noncitizen who has been convicted of a crime in the United States. Not all criminal aliens are removable (see " Defining "Criminal Aliens" "). Despite its widespread use, no consistent definition of the term "criminal alien" exists. In this report, CRS uses "criminal aliens" to refer to any noncitizen who has ever been convicted of a crime in the United States. Certain criminal offenses also have immigration-related consequences, such as being grounds for removal; and certain categories of criminal (and noncriminal) aliens are also the subjects of special ICE enforcement programs, including those described in this report. Criminal immigration offense : A violation of federal criminal immigration law under Title 8 or Title 18 of the U.S. Code. The most common of such violations for which aliens are convicted are 8 U.S.C. §1326 (reentry of a deported alien), 8 U.S.C. §1324 (bringing in and harboring certain aliens), 15 U.S.C. §1546 (fraud and misuse of visas, permits, and other documents), and 8 U.S.C. §1325 (entry of alien at improper time or place). Fugitive alien : An alien who has failed to leave the United States following the issuance of a final order of removal, deportation, or exclusion. Fugitive aliens were referred to as "absconders" prior to FY2007. Fugitive aliens may or may not have criminal records. Removable alien : An alien subject to formal removal (deportation) from the United States. This includes aliens who are inadmissible under INA §212 or deportable under INA §237, including nonimmigrant aliens who enter legally but violate the terms of their visas or overstay their visas. Most removable aliens have never been convicted of a criminal offense. Removable criminal alien : An alien who has been convicted of a removable criminal offense; such an alien is subject to removal from the United States. Removable criminal offense : A criminal offense described in §237(a)(2) of the Immigration and Nationality Act (INA), including crimes of moral turpitude, aggravated felonies, high-speed flight from an immigration checkpoint, failure to register as a sex offender, drug offenses, firearm offenses, and immigration-related document fraud, among others. Appendix B. History of Criminal Alien Removal Programs In 1986, with passage of the Immigration Reform and Control Act ( P.L. 99-603 ), Congress made deporting aliens who had been convicted of certain crimes a formal enforcement priority. The law required the Attorney General "in the case of an alien who is convicted of an offense which makes the alien subject to deportation … [to] begin any deportation proceeding as expeditiously as possible after the date of the conviction." The former Immigration and Naturalization Service (INS) established a pair of programs in 1988 to comply with this requirement: the Institutional Removal Program (IRP) and the Alien Criminal Apprehension Program (ACAP). The programs forged partnerships with corrections facilities to identify deportable aliens convicted of crimes before their release from prison. They also worked with the Department of Justice's Executive Office for Immigration Review (EOIR) to initiate deportation proceedings against aliens serving sentences for deportable offenses during their period of incarceration. The IRP and ACAP initially focused on aggravated felons, a class of serious criminal aliens created in immigration law by the Anti-Drug Abuse Act of 1988 ( P.L. 100-690 ) and enumerated in §101(a)(43) of the INA. The Anti-Drug Abuse Act defined aggravated felonies to include aliens convicted of murder, drug trafficking, or illegal trafficking in firearms or destructive devices. Between 1990 and 1996, Congress enacted a series of measures that expanded the definition of aggravated felons and created additional criminal grounds for removal. The mandates of the IRP and ACAP likewise expanded to include this broader list of offenses. In 1999, the INS issued an Interior Enforcement Strategy, which named as the agency's top interior enforcement priority the identification and removal of criminal aliens and the minimization of recidivism (i.e., illegal reentry by previously removed aliens). Accordingly, between 1998 and 2002 the INS devoted more resources to the removal of criminal aliens than to all other interior enforcement priorities combined. In the wake of the September 11 terrorist attacks, the new Department of Homeland Security (DHS) focused its enforcement activities on suspected terrorists and homeland defense, but with the continued growth of the foreign-born population after 2000, programs targeting criminal aliens also remained an enforcement priority. Within DHS, the IRP and ACAP initially were managed jointly by Immigration and Customs Enforcement's (ICE) Detention and Removal Operations (DRO) and its Office of Homeland Security Investigations. Between 2005 and 2007, the IRP and ACAP were combined into a single Criminal Alien Program (CAP) program within DRO. In 2010, DRO was renamed Enforcement and Removal Operations (ERO). On November 20, 2014, the President issued his Immigration Accountability Executive Order that ended the Secure Communities program and replaced it with the Priority Enforcement Program (PEP). DHS fully implemented PEP in July 2015.

Summary: 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.