Illegal Aliens in
Federal, State, and Local Criminal Justice Systems
Summary
by Rebecca L. Clark and Scott A. Anderson
The Urban Institute
2100 M Street, NW, Washington, DC 20037

OVERVIEW OF PROBLEM
With the rising concern about the numbers and impacts of illegal aliens in the United
States — as evidenced by the sweeping passage of Proposition 187 in California, the immigrant
provisions in 1996 Personal Responsibility and Work Opportunity Reconciliation Act
(PRWORA), and Illegal Immigration Reform and Immigrant Responsibility Act of 1996
(IIRIRA) — criminal illegal aliens have become a subject of particular focus. These individuals
have not only entered or resided in the United States without the knowledge or permission of the
U.S. government, but, while here, they have also violated the laws of the nation, its states, or
municipalities.
At state and local levels, the costs of arresting, prosecuting, sentencing, and supervising
criminal illegal aliens has become a major issue. Six states have filed suits to force the federal
government to reimburse them for criminal justice costs associated with illegal aliens. They have
argued that it is the federal government's responsibility to keep illegal aliens out of this country
and to expel illegal aliens who have gained entry, and that, therefore, the federal government
should offset any fiscal impacts that these illegal aliens have on lower levels of government
through direct reimbursement. None of these suits has been successful.
The federal government has taken some steps to reimburse states for some of the costs
associated with criminal illegal aliens. Section 510 of the Immigration Reform and Control Act
of 1986 (IRCA) authorized the Attorney General to reimburse states for the criminal justice costs
attributable to undocumented persons. No appropriations for illegal aliens were made until 1994,
when the Violent Crime Control and Law Enforcement Act (Public Law 103-317 or the Crime
Act of 1994) authorized $1.8 billion over six years to reimburse states for criminal justice costs
associated with illegal aliens. The State Criminal Alien Assistance Program (SCAAP) was
established to allocate and distribute these monies.
This research describes the characteristics of illegal aliens in the criminal justice system
at federal, state, and local levels. A goal of this project is to be as nationally representative as
possible, given the limits of existing data sets. The federal-level analysis is based on two data
sets, from the Pretrial Services Act Information System (PSAIS) and the U.S. Sentencing
Commission (USSC), which are representative of individuals involved in the federal criminal
justice system. (The PSAIS contains information on defendants charged with federal offenses
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whom pretrial service officers interview, investigate, or supervise. The USSC Monitoring Data
Base contains information on criminal defendants sentenced according to the Sentencing Reform
Act of 1984.) The state-level analysis is based on data collected for the SCAAP on the seven
states with the most illegal aliens, Arizona, California, Florida, Illinois, New Jersey, New York,
and Texas (Warren 1997). All of these states except Illinois filed suits to force the federal
government to reimburse them for criminal justice costs associated with illegal aliens. The
local-level analysis is limited to one site, Cook County, Illinois, and is based on data collected
from the INS District Office and the Cook County Department of Corrections.

KEY FINDINGS
1. How many illegal aliens are there in prison and elsewhere in the criminal justice system?
USSC
Y

In 1995, there were 4,081 illegal aliens sentenced in federal district courts, 11 percent
of the total sentenced.

PSAIS
Y

As in the USSC data, in 1995, illegal aliens represented a high share (14.4 percent) of
individuals entering the Pretrial Services Act Information System (PSAIS).

SCAAP
Y

The INS identified 14,262 illegal aliens among state prisoners in 1995 from
California, Texas, New York, Florida, Illinois, Arizona, and New Jersey. INS was
unable to determine the legal status of 48 percent of foreign-born prisoners in
these states.

Y

California contained a disproportionately large share of illegal alien state prisoners,
71 percent of illegal aliens identified by the INS, which appears to reflect its large
share of the resident illegal alien population and the relatively large share of the
state’s submissions for which the INS was able to determine immigrant/legal
status.

Cook County
Y

There were 228 bookings of individuals identified as illegal aliens by the Cook
County Department of Corrections (CCDC) between 1994 and 1996.

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2. Between 1991 and 1995, how and why has the number of illegal aliens entering the
criminal justice system changed?
USSC
Y

The number of illegal aliens sentenced in federal courts increased by 167 percent ,
compared with 13 percent for citizens. The number of legal aliens declined by 18
percent over this period.

Y

The share of defendants in federal courts who were illegal aliens rose from 4 percent
to 11 percent while the share who were legal aliens declined from 12 percent to 9
percent.

Y

The number of illegal aliens sentenced increased for 89 of the 94 federal district
courts, for all major offense categories, and for all major country of citizenship
groups.

Y

The increase in the number of illegal aliens appears to be partially attributable to
improved border enforcement on the Southwest border—where increases were
largest; growth in the resident illegal alien population; and improved identification
of illegal aliens in the USSC data and by law enforcement officials.

Y

The sharp increase in the number of illegal aliens sentenced is responsible for more
than half of the overall increase in the number of defendants sentenced in federal
courts and 44 percent in the growth in costs of federal post-sentencing
incarceration and supervision.

PSAIS
Y

The number of illegal aliens entering the PSAIS increased by 45 percent, more than
the increase for the resident undocumented alien population, 30 percent. Most of
the increase occurred between 1994 and 1995.

Y

Almost the entire increase in the number of illegal aliens entering the PSAIS can be
explained by an increase in the number of illegal aliens arrested for immigration
offenses between 1994 and 1995; most of the new apprehended immigration
offenders in 1995 were from California.

3. What types of offenses have illegal aliens been convicted of? How do the types of
offenses compare with the general population?
USSC
Y

The major offenses for which illegal aliens were convicted in federal court in 1995
were unlawfully entering the United States (47 percent of the total), drug
trafficking (27 percent), other immigration offenses (11 percent) and fraud
(5 percent).

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Y

Illegal aliens sentenced in federal courts were more likely than legal aliens or
U.S. citizens to have at least one prior conviction resulting in a sentence of at least
60 days.

Y

For U.S. citizens and legal aliens, drug trafficking and fraud were the most common
major federal offense conviction.

PSAIS
Y

In 1995, illegal aliens were more likely to be charged with an immigration offense
(60 percent) or drug trafficking (22 percent) than any other offense. Legal aliens
and citizens were most likely to be charged with drug trafficking offenses
(50 percent and 35 percent respectively).

SCAAP
Y

The most common offenses for which illegal aliens were convicted were drug
offenses in all states except Florida. For states distinguishing among types of
drug offenses, drug trafficking was more common than drug possession, except in
Texas.

Y

In Florida, the most common offense among illegal aliens in state prisons was murder.
Both illegal and legal aliens in Florida were far more likely than aliens in other
states to have been convicted of violent offenses against a person.

Y

In Florida, the high share of murders, and other violent crimes against individuals,
among illegal aliens cannot be attributed to any one country of origin group. For
each major country of origin groups murder and other violent crimes were
substantially more common in Florida than they were in the other major
immigrant states. The large share of violent offenders in Florida may be related to
Florida’s policies on deporting criminal aliens.

Cook County
Y

About 14 percent of CCDC illegal aliens have at least one prior conviction.

Y

Like the general CCDC population, the most common charges for illegal aliens are
drug offenses. Among illegal aliens, Mexicans are less likely than non-Mexicans
to have been charged with drug offenses.

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4. What types of illegal aliens are in the criminal justice system? What are their
characteristics?
USSC
Y

In 1995, California accounted for more illegal aliens sentenced in federal courts than
any other state, 31 percent of the total. Texas had the next highest number of
illegal aliens, 18 percent; together these two states accounted for about half of the
illegal aliens sentenced. Other states with large number of illegal aliens sentenced
were New York, Arizona, Florida, Oregon, and Washington.

Y

Mexicans made up the largest share of illegal aliens sentenced in federal court. The
second largest group was Colombians, followed by Dominicans, Jamaicans, and
Nigerians. Mexicans dominated in most of the major immigration states, but
Colombians were the largest group in New York, Florida, and New Jersey.

Y

Major offenses among illegal aliens differed significantly by country of citizenship.
In 1995, Mexicans were the only group for which unlawful entry was the
dominant offense. Colombians were the only group for which drug trafficking
was the dominant offense and for which a substantial share were convicted of
money laundering. Nigerians were the only group for which fraud constituted a
major offense.

SCAAP
Y

Mexico was the dominant country of origin among illegal alien state prisoners in
Arizona, California, Texas, and Illinois. In New York, Florida, and New Jersey,
illegal immigrants from the Caribbean and from Central and South America
constituted the largest shares of illegal aliens in state prisons, although in these
states no single country or country group dominated.

Y

The vast majority of illegal alien state prisoners entered the United States illegally,
rather than entering the country legally and then remaining after their authorized
period of stay had expired. Texas and California had the largest share of illegal
aliens who entered without inspection — 94–95 percent — while shares for
Illinois and New Jersey were the lowest — 85–86 percent.

Y

Types of offense committed differed by country of origin. Colombians and
Dominicans were especially likely to have been imprisoned for drug-related
offenses. Among Haitians and Nicaraguans, drug offenses were relatively
uncommon.

Cook County
Y

Eighty-five percent of illegal aliens detained by the CCDC were citizens of Mexico.
The second most common country of citizenship was Colombia, accounting for
4 percent.

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Y

Among Mexican illegal aliens, most are from the interior Mexican states, such as
Guerrero, the largest contributor with 12 percent of the total. Few are from states
bordering the United States.

Y

Eighty-nine percent of illegal aliens in the CCDC entered the United States entered
without inspection. Mexicans were substantially more likely to have entered
without inspection than illegal aliens from other countries.

Y

Nearly half of illegal aliens in the CCDC (46 percent) entered the United States at San
Ysidio, California near San Diego. Other major points of entry were El Paso,
Texas (13 percent), Nogales, Arizona (11 percent), and Laredo, Texas (9 percent).

Y

An overwhelming majority of illegal aliens in the CCDC appear to be U.S. residents.
Ninety percent had been in the United States for at least a year; none been in this
country for less than a month. Furthermore, 14 percent have one or more U.S.
citizen children.

Y

About 8 percent of illegal aliens in the CCDC have already been deported at least
once.

5. What are the socioeconomic and demographic characteristics of illegal aliens in prison
or in other parts of the criminal justice system? How do they compare with others
in the criminal justice system?
USSC
Y

Sentenced illegal aliens, compared with legal aliens and U.S. citizens, were poorer,
had lower educational attainment, were younger, were more likely to be Hispanic,
were more likely to be male, and were less likely to have dependents.

PSAIS
Y

Illegal aliens entering the PSAIS were less educated, younger, and more likely to be
white and Hispanic than legal aliens and citizens. The illegal aliens were more
likely to be married than citizens but less likely than legal aliens.

SCAAP
Y

In most states, illegal aliens in state prisons were younger, on average, than legal
aliens.

Cook County
Y

Illegal aliens are younger on average than the general CCDC population; 44 percent
are under age 25, compared with 32 percent overall.

Y

A majority of illegal aliens in the CCDC are involved in construction trades, most
often as laborers.
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DISCUSSION
Accuracy in identifying illegal aliens
One potential problem with this analysis is that it is not clear that all aliens are identified
as such, particularly in the PSAIS, USSC, and SCAAP data. If law enforcement officials
misidentify some aliens as natives, then the process of ascertaining exact immigrant/legal status
is never begun, so illegal aliens are not identified. Misidentification as natives would probably
be limited to aliens who are not arrested for immigration offenses and who, among those charged
with federal offenses, at least, could produce a social security number.
According to the federal officials we spoke with, there are no formally established
policies to ensure that all aliens, particularly illegal aliens, are identified as such in the USSC and
PSAIS. The procedures they described seem adequate, especially USSC procedures such as
investigating all individuals who cannot produce a social security number and asking detailed
questions about defendantsG family members, especially the location of their parents.
Establishing standard guidelines for deciding whether an individualGs immigration status should
be determined would probably reduce the likelihood that aliens are misidentified as natives,
especially in areas where few aliens are apprehended.
Federal officials told us that, once an individual was identified as possibly being an alien,
their status was determined by either talking to INS officials or accessing INS records. Given the
INSGs own difficulties in determining the immigrant/legal status of the prisoners whose names
were submitted by states for reimbursement under SCAAP, which lead to a match rate of only 52
percent in 1995 for the seven states we examined, it is surprising that the missing data rates for
the PSAIS and USSC data were so low. We were unable to determine the exact procedures used
for PSAIS and USSC status determination, but it seems likely that defendants who could not be
matched to INS records were assumed to be illegal aliens, although our research suggests that
some individuals who cannot be matched to INS records are not illegal aliens. One explanation
for the high level of immigrant/legal status determination in the USSC and PSAIS data is that a
large share of the individuals identified as illegal aliens in the data bases were charged or
convicted of unlawfully entering the United States, which, as an offense that only applies to
illegal aliens, contains within it the immigrant/legal status identification of the defendant. At the
state level, there are no offenses that can be used to automatically assign immigrant/legal status.
One method of further investigating the accuracy of immigrant/legal status determination would
be to match defendants in the USSC and PSAIS data to INS records in a process similar to that
used for SCAAP. (The match rate for state SCAAP submissions rose to 70 percent by 1995,
suggesting matching procedures have improved.)
Improving the efficiency of identifying illegal aliens
One issue that we were not able to resolve is whether there is duplication of effort
involved in identifying the immigrant/legal status of federal defendants. It is possible that for
some defendants, immigrant/legal status is determined three times, once in the pretrial period,
another time before sentencing, and a final time after conviction, by INS officials screening for
potentially deportable criminal aliens. Putting in place a system through which the information
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from each status determination, including its source, is passed along through the different stages
of the criminal justice system could potentially cut down on the time it takes to process foreignborn prisoners and would allow refinement of the procedures used to identify aliens, particularly
illegal aliens.
One problem we identified was the difficulty in consistently recording names that follow
Spanish surname conventions, which often include two-part last names. Matching individuals
within and across data sets would be considerably easier and more efficient if a single convention
for recording these last names was developed and disseminated to all governmental law
enforcement agencies who have responsibility for dealing with large numbers of foreign-born
individuals. Adoption of such a convention would be advantageous to all levels of government
because it would facilitate the identification of potentially deportable criminal aliens.
Recent General Accounting Office reports have identified difficulties the INS has in
tracking potentially deportable criminal aliens(U.S. General Accounting Office, 1997a, 1998).
Recent improvements in making status determinations for SCAAP submissions suggests the
INS’s performance is improving. Having integrated, up-to-date INS data systems would reduce
the workload of pretrial services officers and would improve the information magistrates and
judges have when making the decision whether to detain or release federal defendants.
Explaining why the number of illegal aliens in the federal criminal justice system has
increased
While this analysis of federal data sets has shown that the number of illegal aliens in the
federal criminal justice has increased sharply, our ability to explain this increase was limited. It
appears to be due in part to increased border enforcement, better identification of illegal aliens,
and the growth of resident illegal alien population, although other factors may play a role. Data
such as the PSAIS and USSC are only of limited use in determining the causes for changes in
criminal activity. We were able to show that, following the introduction of Operations Hold the
Line and Gatekeeper, the number of illegal alien defendants charged with and convicted of
unlawful border crossing increased, although convictions for this offense also rose in virtually all
districts, not just the two that were home to the initiatives. Lacking any details in the data sets
about the law enforcement initiatives that were associated with each arrest, conclusions about the
link between enforcement and arrests are suggestive, but not conclusive. However, ability to
track changes in levels of criminal activity among illegal aliens would be improved if more data
about aliens were collected.
With the PSAIS and USSC data, it is not possible to calculate prosecution or conviction
rates for the entire illegal alien population. While these data sets provide estimates of the
number of illegal aliens charged with and convicted of federal offenses, the denominator for the
rate cannot be calculated. The INS produces estimates of the resident illegal alien population of
the United States, but it is clear from the description of offenses, specifically the large share of
illegal aliens convicted of unlawful entry in border states, that a tremendous share of the illegal
aliens appearing in the PSAIS and USSC are not resident illegal aliens; they are recent border
crossers. An unknown share of illegal aliens convicted of other offenses are also recent arrivals.
In order to calculate prosecution and conviction rates for resident illegal aliens, it would be
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necessary to add information for illegal aliens’ length of stay in the United States to the PSAIS
and USSC data sets. Attributing all offenses committed by illegal aliens to the resident illegal
alien population would result in a gross overestimate of the criminal propensity of this
population.
The PSAIS and USSC data also cannot be used to assess the level of criminal
involvement of immigrants who entered the country legally. Using these data would
underestimate criminal involvement among immigrants admitted legally because the data sets do
not distinguish between naturalized citizens and U.S. natives.
The number of legal aliens sentenced in federal court declined dramatically between
1994 and 1995. This decline took place in virtually all districts, not just in border areas. More
research should be done to determine the reasons for this decline, whether it was also observed at
state and local areas, and whether it continued through the rest of the 1990s. Since legal aliens’
crime rates were already declining when the Illegal Immigration Reform and Immigrant
Responsibility Act of 1996 was passed, it may be difficult to assess whether this law will have an
effect on legal aliens’ criminal activity.
Implications for developing strategies for reducing crimes committed by illegal aliens
The analysis of Cook County and of the SCAAP data from California, New York, Texas,
Florida, Illinois, New Jersey, and Arizona shows that the vast majority of illegal alien offenders
in these areas were individuals who entered without the knowledge or permission of the U.S.
government (“EWIs” for entered without inspection) rather than individuals who were admitted
legally but remained in the United States after their authorized period of stay had ended
(“overstays”). If a primary goal of detecting and removing illegal aliens is to reduce criminal
activity, then resources are better expended targeting EWIs rather than overstays.
Our Cook County analysis suggests that a large proportion of illegal aliens apprehended
at the local level are long-term settlers. Further research needs to be done in order to assess
whether this finding also holds true in other areas and in the federal courts. Assessing the
relative impact of long-term and short-term illegal aliens on overall level of crime in the United
States would be useful in two ways. First, it would help policy makers and law enforcement
officials assess the effects of increased border enforcement activities on illegal aliens’
participation in crimes other than unlawful entry. Second, when deciding whether to seek out
and deport long-term illegal residents, policy makers should have access to accurate assessments
of their criminal activity; the costs of the resident illegal aliens will be overestimated if all crimes
committed by illegal aliens, regardless of their length of residence, are ascribed to the resident
illegal alien population.
The increase in prosecutions and convictions of illegal aliens appears to have significantly
affected both the number and the estimated costs of incarcerating and supervising of defendants
convicted in federal courts. Since a substantial share of the increase in illegal aliens convicted
appears to be due to increased border enforcement, this increased burden on the federal criminal
justice system can be seen as a secondary cost of such border enforcement.

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If border interdiction efforts successfully reduce attempted illegal entry, this negative
impact on the federal criminal justice system may be short-term. Furthermore, by reducing the
number of EWIs, whom our analysis suggests are responsible for more criminal offenses than
overstays, successful border control efforts would probably have a particularly large impact on
reducing the amount of criminal activity among illegal aliens.
Reducing the number of illegal aliens entering the United States may affect crime rates
far beyond the U.S.-Mexican border. The Cook County analysis shows that 46 percent of illegal
aliens arrested had entered at San Ysidio, near San Diego and part of Operation Gatekeeper, and
13 percent had entered at El Paso, home of Operation Hold the Line. If these and similar
operations actually reduce illegal entry, rather than simply shifting it to other regions, Cook
County, and probably other areas, will eventually see a reduction in the number of illegal aliens
apprehended for criminal activity.
A recent General Accounting Office (1997) report suggests that the effects of INS’s
southwest border strategy are inconclusive. Analysis based on INS I-213 forms, similar to our
analysis for Cook County, may be enlightening because these forms include information on legal
status and date of entry for foreign-born arrestees. Rather than relying on overall crime trends, as
has been done in the past, analysts would be able to track whether, in border areas, arrests of
recently arrived illegal aliens have declined since these border efforts have been introduced. A
complete assessment would also include adjacent areas, which have become more popular entry
points for illegal aliens, and selected other non-border sites, such as Cook County, where illegal
aliens who entered at or near San Diego and El Paso dominate the apprehended illegal aliens.

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