Estimates of the size of the alien population subject to removal vary. A report from the Pew Research Center estimated the population of unauthorized aliens in the United States to be approximately 12 million as of March 2006. According to DHS, the population of aliens subject to removal from the United States has grown in recent years. DHS’s Office of Immigration Statistics estimated that the population of aliens subject to removal has increased by half a million from January 2005 to January 2006. Additionally, DHS has estimated that the removable alien population grew by 24 percent from 8.5 million in January of 2000 to 10.5 million in January of 2005. Aliens who are in violation of immigration laws are subject to removal from the United States. Over 100 violations of immigration law can serve as the basis for removal from the United States, including, among other things, criminal activity, health reasons (such as having a communicable disease), previous removal from the United States, and lack of proper documentation. ICE investigations resulted in 102,034 apprehensions, or about 8 percent of the approximately 1.3 million DHS apprehensions in 2005. Four main categories constituted the basis for aliens removed by DHS in 2005: (1) aliens entering without inspection, by, for example, illegally crossing the border where there is no formal U.S. port of entry; (2) aliens attempting to enter the United States without proper documents or through fraud, at U.S. ports of entry; (3) aliens with criminal convictions or believed to have engaged in certain criminal activities, such as terrorist activities or drug trafficking; and (4) aliens who are in violation of their terms of entry (e.g., expired visa). Our review of ICE policies and procedures, along with interviews at ICE field offices, showed that officers exercise discretion throughout various phases of the alien apprehension and removal process, but the initial phases of the process—initiating removals, apprehending aliens, issuing removal documents and detaining aliens—involve the most discretion. Officers in OI and DRO field offices told us that they exercise discretion for aliens with humanitarian issues and aliens who are not investigation targets on a case-by-case basis with guidance and approval from supervisors. Officers told us they typically encounter (1) aliens who are the target of an investigation and (2) aliens who are not the target of an investigation but who are encountered through the course of an operation and are subject to removal. While officers told us that discretion with regard to aliens who are fugitives, criminals, and other investigation targets is limited by clearly prescribed policies and procedures, they told us that they have more latitude to exercise discretion when they encounter aliens who are not fugitives or criminals and are not targets of ICE investigations, particularly when encountering aliens with humanitarian issues. The alien apprehension and removal process encompasses six phases: (1) initial encounter, (2) apprehension, (3) charging, (4) detention, (5) removal proceedings, and (6) final removal. Our review of federal regulations, ICE policies, guidance, and interviews showed the parts of the removal process from the time officers encounter aliens as part of an operation to the time they determine whether to detain an alien involve the most discretion. During removal proceedings and final removal, ICE attorneys and DRO officers can exercise discretion only in clearly delineated situations prescribed by ICE policies and statutory and regulatory requirements. Officers told us that during the initial phases of the apprehension and removal process, they encounter situations that require them to pursue alternate ways to initiate removals, in lieu of apprehending aliens. During encounters with aliens, officers told us that they decide how to exercise discretion for aliens on a case-by-case basis with input from supervisors or experienced officers. Specifically, officers told us that they exercise discretion when they encounter aliens who (1) present humanitarian concerns such as medical issues or being the sole caregiver for minor children or (2) are not the primary target of their investigations. DRO and OI officers told us that their primary goal is to initiate removal proceedings for any alien they encounter who is subject to removal. However, officers told us that in some instances, they might decide not to pursue any action against an alien who they suspect to be removable. Officers at two OI and one DRO field office told us that, in some instances, they are unable to initiate removal action against every alien they encounter during the course of an operation. Officers noted that several factors—such as the availability of detention space, travel time to an alien’s location, and competing enforcement priorities—affect their decisions to initiate removal action against an alien. Officers at one of the seven OI field offices we visited also told us that because of limited resources they have to make trade-offs between dedicating resources to aliens who pose a threat to public safety and those who do not—that is, noncriminal aliens—which in some instances result in decisions to not initiate removal action against noncriminal aliens. Our review of DHS and ICE guidance showed that officers’ ability to exercise discretion is limited for aliens who are investigation targets, such as criminal aliens and fugitive aliens who have ignored a final removal order. Discretion for apprehending these aliens is limited due to clearly prescribed policies, and procedures—such as requirements under the INA to detain terrorists or certain criminals—governing the handling of these aliens. By contrast, officers at all seven DRO and seven OI field offices we visited told us that they have discretion to process and apprehend aliens who are not investigation targets or aliens who present humanitarian circumstances. In such circumstances, officers told us that they can exercise discretion by deciding to (1) apprehend an alien and transport the alien to an ICE facility for processing, (2) issue the alien an NTA by mail, or (3) schedule an appointment for the alien to be processed at an ICE facility at a later date. For example, in looking for a criminal alien who is the target of an investigation, a fugitive operations team may encounter a friend or relative of the targeted alien—who is also removable—but not the primary target of an ICE investigation. If the friend or relative has a humanitarian circumstance, like being the primary caregiver for small children, the officers can decide to not apprehend the friend or relative and opt for processing at a later time after reviewing the circumstances of the case and determining that no other child care option is available at the time. In such instances, ICE headquarters officials told us that officers are to confirm child welfare claims made by an alien and determine whether other child care arrangements can be made. Headquarters officials also told us that aliens do not always divulge that they are the sole caretakers of children but explained that if ICE agents became aware of an alien’s child welfare responsibility, agents must take steps to ensure that the child or children are not left unattended. In addition, officers at two OI offices and one DRO office told us that in some instances, such as when aliens are sole caretakers for minor children or are ill, they will schedule appointments for aliens who are not investigation targets to process them at a later date. Officers at five of the seven OI field offices and two of the seven DRO offices we visited also told us that they will mail an NTA—as an alternative to apprehension—to aliens who present humanitarian issues such as medical conditions or child welfare issues. At another OI field office, officers told us that when determining whether to apprehend aliens or use an alternative to apprehension—for aliens who are not investigation targets—they also consider manpower availability. Our review of ICE guidance and procedures showed that most of an officer’s discretion in the charging phase relates to the decision to grant voluntary departure. Officers told us that when not statutorily prohibited from granting voluntary departure, they have some discretion in determining whether to issue an NTA and thus initiate formal removal proceedings or grant voluntary departure in lieu of initiating formal removal proceedings, which typically results in a hearing before an immigration judge. Officers told us that they may consider factors like humanitarian concerns and ICE priorities when exercising discretion to grant voluntary departure. On the basis of our review of ICE data, we noted significant variation in the use of voluntary departure across field offices. Our review of OI apprehension data also showed that three OI field offices near the U.S. southwestern border initiated a relatively higher number of voluntary departures (equal or greater than the number of NTAs issued). ICE headquarters officials noted that officers at field offices near the U.S. southwestern border employ voluntary departure generally because of their proximity to the U.S.-Mexico border, which enables them to easily transport Mexican nationals to Mexico. Figure 1 illustrates the number of NTAs and voluntary departure issued by OI field offices. Our review of procedures also showed that if detention is not mandated by the INA, officers have discretion to determine if an alien will be detained or released pending the alien’s immigration court hearing. When making this determination, ICE guidance instructs officers to consider a number of factors, such as humanitarian issues, flight risk, availability of detention space, and whether the alien is a threat to the community. Officers at two DRO field offices we visited told us that they exercise discretion to release aliens from custody if appropriate facilities are not available or if detention space is needed for aliens who pose a greater threat to public safety. At one OI field office, officers provided an example of an operation where they released two women and two children on their own recognizance because of the lack of appropriate detention space to house women and children. Officers at another DRO field office also noted that detaining women and juveniles can be challenging because of limited space to accommodate them. Detention determinations made by officers can be reexamined by immigration judges upon an alien’s request.