Page 1 GAO-05-646R 

May 9, 2005 

The Honorable John N. Hostettler 

Chairman, Subcommittee on Immigration, 

 Border Security, and Claims 

Committee on the Judiciary 

House of Representatives 

The Honorable Steve King 

House of Representatives 

The Honorable Melissa Hart 

House of Representatives 

Subject: Information on Certain Illegal Aliens Arrested in the United 

States

The former Immigration and Naturalization Service estimated that as of 

January 2000 the total unauthorized immigrant population residing in the 

United States was 7 million.1

 This total includes those who entered the 

United States illegally and those who entered legally but overstayed their 

authorized period of stay. A more recent study estimated that there were 

about 10 million illegal aliens living in the United States as of March 2005.2

The study estimated that nearly 700,000 aliens entered the United States 

illegally or overstayed their authorized period of stay each year between 

2000 and 2004. Some illegal aliens in the United States have been arrested 

and incarcerated in federal and state prisons and local jails, adding to 

already overcrowded prisons and jails. 

On April 7, 2005, we issued a report on criminal aliens3

 that were 

incarcerated in federal and state prisons and local jails.4

 Our report 

 1

Estimates of the Unauthorized Immigrant Population Residing in the United States: 

1990 to 2000, Office of Policy and Planning, U.S. Immigration and Naturalization Service. 

2

Estimates of the Size and Characteristics of the Undocumented Population, Jeffrey S. 

Passel, Pew Hispanic Research Center, March 2005. 

3

An alien legally or illegally in the United States who has been convicted of a crime. 

4

GAO, Information on Criminal Aliens Incarcerated in Federal and State Prisons and 

Local Jails, GAO-05-337R (Washington, D.C.: April 7, 2005). 

United States Government Accountability Office

Washington, DC 20548 
Page 2 GAO-05-646R 

contained information on the number of criminal aliens incarcerated, their 

country of citizenship or country of birth, and the cost to incarcerate 

them. You also requested that we provide information on the criminal 

history of aliens incarcerated in federal and state prisons or local jails who 

had entered the country illegally. For a population of aliens that entered 

the country illegally and were incarcerated in federal or state prisons or 

local jails, this report addresses the following questions: 

• How many times have they been arrested? 

• How many and what type of criminal offenses have they been arrested for? 

• What states were they arrested in? 

To obtain information to answer these objectives, we identified a 

population of 55,322 aliens that the U.S. Immigration and Customs 

Enforcement (ICE) in the Department of Homeland Security determined, 

based upon information in its immigration databases, had entered the 

country illegally and were still illegally in the country at the time of their 

incarceration in federal or state prison or local jail during fiscal year 2003. 

We then analyzed selected data contained in the criminal history record, 

commonly referred to as the rap sheet, of these illegal aliens maintained 

within the Federal Bureau of Investigation’s (FBI) Integrated Automated 

Fingerprint Identification System (IAFIS).5

 To assess the reliability of 

immigration databases used to make the determination about an alien’s 

legal status, we discussed internal control processes for ensuring data 

quality with responsible ICE staff and found the data to be reliable for 

purposes of this report. To assess the reliability of IAFIS data, we 

discussed the data collection methods and internal control processes for 

ensuring data quality with responsible FBI staff and reviewed relevant 

policies and procedures. IAFIS may not contain all of the arrests for the 

illegal aliens in our study population since seven states report only their 

first arrest to the FBI. Subsequent arrest data is available only from the 

state’s criminal history record system. While the magnitude of any 

undercount is unknown, we found that the data we used for our analyses 

were sufficiently reliable for the purposes of this report. 

 5

IAFIS contains the fingerprints and corresponding criminal history for more than 47 

million subjects. The fingerprints and corresponding criminal history information are 

submitted voluntarily by federal, state and local law enforcement agencies. 
Page 3 GAO-05-646R 

Several things should be noted regarding our analysis. First, an arrest does 

not necessarily result in a prosecution or a conviction. Second, our 

analysis is limited to the aliens that ICE determined to have entered the 

United States illegally. Third, since all arrests for an individual may not be 

recorded in IAFIS, our data represent the minimum number of arrests for 

these illegal aliens. Last, our analysis is not designed to infer conclusions 

about the arrest history of other illegal aliens not in our study population 

who entered the country illegally and have been arrested. 

In April, we discussed with your offices the results of our work. This 

report conveys the information provided during those discussions (see 

encl. I). 

We performed our work from October 2004 through May 2005 in 

accordance with generally accepted government auditing standards. 

Further details on our scope and methodology, including how we selected 

the illegal aliens in our study population, are discussed in enclosure II. 

The briefing slides in enclosure I address each of our three questions. In 

summary, for our study population of 55,322 illegal aliens, we found that: 

• They were arrested at least a total of 459,614 times, averaging about 8 

arrests per illegal alien. Nearly all had more than 1 arrest. Thirty-eight 

percent (about 21,000) had between 2 and 5 arrests, 32 percent (about 

18,000) had between 6 and 10 arrests, and 26 percent (about 15,000) had 11 

or more arrests. Most of the arrests occurred after 1990. 

• They were arrested for a total of about 700,000 criminal offenses, 

averaging about 13 offenses per illegal alien. One arrest incident may 

include multiple offenses, a fact that explains why there are nearly one 

and half times more offenses than arrests.6

 Almost all of these illegal aliens 

were arrested for more than 1 offense. Slightly more than half of the 55,322 

illegal aliens had between 2 and 10 offenses. About 45 percent of all 

offenses were drug or immigration offenses. About 15 percent were 

property-related offenses such as burglary, larceny-theft, motor vehicle 

theft, and property damage. About 12 percent were for violent offenses 

such as murder, robbery, assault, and sex-related crimes. The balance was 

 6

For example, a burglar may enter a home, steal some of the victim’s property, and drive 

away in the victim’s car. If arrested, the person could be charged with three offenses, 

burglary, theft, and motor vehicle theft. 

Results 
Page 4 GAO-05-646R 

for such other offenses as traffic violations, including driving under the 

influence; fraud—including forgery and counterfeiting; weapons 

violations; and obstruction of justice. 

• Eighty percent of all arrests occurred in three states—California, Texas, 

and Arizona. Specifically, about 58 percent of all arrests occurred in 

California, 14 percent in Texas, and 8 percent in Arizona. 

The Departments of Justice and Homeland Security reviewed a draft of 

this report and had technical comments, which we incorporated as 

appropriate. 

We are sending copies to the Departments of Justice and Homeland 

Security and interested congressional committees, and we will make 

copies available to others who request them. In addition, the report will be 

available at no charge on GAO’s Web site at http://www.gao.gov. 

If you or your staff have any questions concerning this report, please 

contact me at (202) 512-8816 or by e-mail at Stanar@gao.gov or Michael 

Dino, Assistant Director, at (213) 830-1150 or Dinom@gao.gov. Key 

contributors to this report were Amy Bernstein, Ann H. Finley, Evan 

Gilman, Frederick Lyles, Jr., Jan Montgomery, Karen O’Conor, Jason 

Schwartz, and Laura Czohara. 

Sincerely yours, 

Richard M. Stana, Director 

Homeland Security and Justice Issues 

Agency Comments 

and Our Evaluation 
Enclosure I: Briefing Slides 

Page 5 GAO-05-646R 

Enclosure I: Briefing Slides 

1

Information on Certain Illegal Aliens 

Arrested in the United States

Briefing for Congressional Requesters

April 2005
Enclosure I: Briefing Slides 

Page 6 GAO-05-646R 

2

Introduction

• In April 2005, we issued a report, Information on Criminal Aliens Incarcerated in 

Federal and State Prisons and Local Jails, (GAO-05-337R). This report contained 

information on the number of criminal aliens we identified that were incarcerated, 

their country of citizenship or country of birth, and the cost to incarcerate them. 

• You also requested that we provide information on the criminal history of aliens 

incarcerated in federal and state prisons or local jails who had entered the country 

illegally. 
Enclosure I: Briefing Slides 

Page 7 GAO-05-646R 

3

Objectives

For a population of aliens incarcerated in federal and state prisons and local 

jails during fiscal year 2003 who entered the country illegally, we address the 

following questions:

(1) How many arrests did they have? 

(2) How many and what type of criminal offenses have they been 

arrested for?

(3) What states were they arrested in? 
Enclosure I: Briefing Slides 

Page 8 GAO-05-646R 

4

Results in Brief

How many arrests did these illegal aliens have?

For our study population of 55,322 illegal aliens:

• They were arrested at least a total of 459,614 times, averaging 

about 8 arrests per illegal alien.1

• Ninety-seven percent had more than 1 arrest. About 38 

percent had between 2 and 5 arrests, 32 percent had between 

6 and 10 arrests, and 26 percent had over 11 arrests.

• Eighty-one percent of all arrests occurred after 1990.

1An arrest does not necessarily result in a prosecution or a conviction.
Enclosure I: Briefing Slides 

Page 9 GAO-05-646R 

5

Results in Brief

How many and what type of criminal offenses were they arrested for?

For our study population of 55,322 illegal aliens:

• They were arrested for at least a total of nearly 700,000 criminal offenses, averaging 13 

offenses per alien.

• About 24 percent were drug offenses.

• About 21 percent were immigration offenses.

• About 15 percent were property-related offenses such as burglary, larceny-theft, motor 

vehicle theft, and property damage.

• About 12 percent were for murder, robbery, assault, and sexually related crimes.

• The remaining 28 percent were for other offenses such as traffic violations, including 

driving under the influence; fraud—including forgery and counterfeiting; weapons violations; 

and obstruction of justice.
Enclosure I: Briefing Slides 

Page 10 GAO-05-646R 

6

Results in Brief

What states were they arrested in?

For our study population of 55,322 illegal aliens:

• Eighty percent of all arrests occurred in the following 3 states.

California 58 percent

Texas 14 percent

Arizona 8 percent 
Enclosure I: Briefing Slides 

Page 11 GAO-05-646R 

7

Background

• When an individual is taken into custody, the arresting law enforcement agency captures the 

arrest charge(s), fingerprints, and personal identifiers of the individual. This information is 

submitted to the FBI’s Integrated Automated Fingerprint Identification System (IAFIS), which is 

responsible for preserving identification and criminal history records for felony and serious 

misdemeanor offenses. The FBI assigns an FBI identification number to each set of fingerprints. 

• Generally, all aliens arrested by the DHS’s U.S. Immigration and Customs Enforcement (ICE) are 

assigned an alien identification number. This allows ICE to establish and track an alien’s 

immigration history. 

• For illegal aliens incarcerated in state prisons and local jails, the federal government has 

reimbursed state and local governments that apply for reimbursement for a portion of their 

incarceration costs through the Department of Justice’s (DOJ) State Criminal Alien Assistance 

Program (SCAAP), managed by the Bureau of Justice Assistance (BJA).
Enclosure I: Briefing Slides 

Page 12 GAO-05-646R 

8

Scope and Methodology—Study Population of Illegal 

Aliens Used in Our Analysis

Number of unique convicted 36,390 59,427

criminal aliens with a FBI 

identification number and an 

alien identification number 

18,581 36,741

Number of the above unique 

convicted criminal aliens that 

ICE determined to have 

entered illegally

55,322

Total study population of illegal 

aliens used in our analysis 

Number of convicted criminal 46,063 262,105

aliens

Inmates incarcerated by state 

prisons and local jails and 

submitted to SCAAP for 

reimbursement1

Inmates incarcerated in federal 

prison on December 27, 2003

1These represent the inmates incarcerated in state prisons and local jails between July 1, 2002, and June 30, 2003.
Enclosure I: Briefing Slides 

Page 13 GAO-05-646R 

9

Scope and Methodology—Analysis of 

Arrest Data

• For the 55,322 illegal aliens in our study population, we obtained 

and analyzed the arrest history information contained in IAFIS as of 

October 2004.

• The arrest history information contained the date of arrest; the

arresting federal, state, or local law enforcement agency; and a

narrative description of the offense for which the alien was arrested. 

• For purposes of our analysis, we categorized these arrest 

descriptions into 1 of 19 major offense categories, e.g., immigration, 

drugs (see slides 10 and 11).

• In addition, for the 18,581 illegal aliens in our study population who 

were incarcerated in a federal prison, we analyzed related 

conviction information.

1Under 28 U.S.C. 534, the FBI is required to acquire, collect, classify, and preserve, among other things, identification and criminal records.

IAFIS includes individuals who have been arrested for an offense that is classified as a felony or a serious misdemeanor.
Enclosure I: Briefing Slides 

Page 14 GAO-05-646R 

10

Scope and Methodology—Crimes Included in Major 

Offense Categories

grand and petty larceny and theft, shoplifting, embezzlement, and money

laundering

Larceny/theft

Kidnapping false imprisonment, kidnapping, and taking hostages

illegal entry, illegal reentry, false claim to U.S. citizenship, alien smuggling, and 

removal proceedings

Immigration

Homicide murder, manslaughter, and homicide

deceptive practices or identification, fraud, giving false information, altering or 

forging documents, and counterfeiting or possession of counterfeit materials or

tools

Fraud, forgery, and

counterfeiting

use/under the influence, possession, possession with intent to distribute, sales,

manufacturing, transporting, and possession of drug paraphernalia

Drugs

Disorderly conduct disturbing the peace, fighting, intoxication, public nuisance, and disorderly conduct

Burglary breaking and entering, burglary, and possession of burglary tools

Assault assault, battery, assault with a deadly weapon, endangerment, and threats

Arson arson, reckless burning, and possession of arson materials

Major offense category Category includes 1 

1All offenses include any attempt or conspiracy to commit the respective offense. We developed the criminal offense categories using the 

FBI’s classification for offense codes as our guidance. 
Enclosure I: Briefing Slides 

Page 15 GAO-05-646R 

11

Scope and Methodology—Crimes Included in Major 

Offense Categories (continued)

includes trespassing, gang participation, littering, child cruelty, racketeering, and 

illegal waste dumping

Other

possession of a weapon, discharging a weapon, altering a weapon, and carrying a 

concealed weapon

Weapons violations

driving under the influence, hit and run, no proof of insurance, no driver’s license, 

and moving violations such as speeding and failure to stop

Traffic violations

Stolen property buying, selling, receiving, or possessing stolen property

lewd and lascivious acts, rape, sexual assault, indecent exposure, prostitution, and 

molestation

Sex offenses

Robbery armed robbery, robbery of a dwelling, robbery of a bank, and unarmed robbery 

Property damage destruction of property, vandalism, and criminal or malicious mischief

escaping, evading, being a fugitive of justice, failing to appear, failing to register as a 

sex offender, resisting arrest, and interfering with or obstructing an officer or justice 

proceedings

Obstruction of justice

Motor vehicle theft auto theft, carjacking, and taking a vehicle without consent

Major offense category Category includes 
Enclosure I: Briefing Slides 

Page 16 GAO-05-646R 

12

Data Limitations

• The FBI’s IAFIS does not include all arrests and offenses–7 states1 report only the 

first arrest and associated offenses to the FBI, subsequent arrest information is 

available only through the state’s criminal history database. Further, some law 

enforcement agencies do not report information on every arrest to the FBI. Also, 

IAFIS does not include minor misdemeanor offenses.

• FBI may reject fingerprint cards that are not readable, and sometimes the submitting 

law enforcement agency does not resubmit the card for entry into IAFIS.

• Results of our analysis pertain only to our study population. Results cannot be 

generalized to all illegal aliens that may have been arrested and therefore cannot be 

interpreted as representing arrest or offense rates for all illegal aliens. 

1 Colorado, Florida, Montana, Oklahoma, Oregon, New Jersey, and North Carolina.
Enclosure I: Briefing Slides 

Page 17 GAO-05-646R 

13

Number of Arrests: 

Ninety-seven percent of illegal aliens in our study 

population had more than one arrest.

-

5,000

10,000

15,000

20,000

25,000

1 2 - 5 6 - 10 11 - 15 16 - 20 21 - 25 26 - 30 31 or

greater

Number of arrests

1,574 (3%)

21,226 (38%)

17,863 (32%)

8,227 (15%)

3,522 (6%)

1,545 (3%) 710 (1%) 655 (1%)

Number of illegal aliens 

(percentage of population)

Note: Percentage totals do not add to 100 because of rounding.

Source: GAO analysis of FBI IAFIS data.

Total number of illegal aliens in our study 

population: 55,322

Total number of arrests: 459,614

Average number of arrests: 8
Enclosure I: Briefing Slides 

Page 18 GAO-05-646R 

14

Number of Arrests: Federal Prison Inmates

Ninety-nine percent of incarcerated illegal aliens had more than 

one arrest.

-

5,000

10,000

15,000

20,000

25,000

1 2 - 5 6 - 10 11 - 15 16 - 20 21 - 25 26 - 30 31 or

greater

Num ber of arrests

200 (1% )

5,486 (30%) 6,245 (34%)

3,431 (18% )

1,665 (9%) 785 (4% ) 390 (2% ) 379 (2% )

Number of illegal aliens 

(percentage of population)

Number of illegal aliens in our study 

population: 18,581

Total number of arrests: 185,168

Average number of arrests: 10

Source: GAO analysis of FBI IAFIS data.
Enclosure I: Briefing Slides 

Page 19 GAO-05-646R 

15

Number of Arrests: State Prison and Local Jail Inmates

Ninety-six percent of incarcerated illegal aliens had more than one arrest.

-

5,000

10,000

15,000

20,000

25,000

1 2 - 5 6 - 10 11 - 15 16 - 20 21 - 25 26 - 30 31 or

greater

Number of arrests

1,374 (4%)

15,740 (43%)

11,618 (32%)

4,796 (13%)

1,857 (5%) 760 (2%) 320 (1%) 276 (1%)

Number of illegal aliens (percentage of population)

Number of illegal aliens in our study 

population: 36,741

Total number of arrests: 274,446

Average number of arrests: 7

Note: Percentage totals do not add to 100 because of rounding.

Source: GAO analysis of FBI IAFIS data.
Enclosure I: Briefing Slides 

Page 20 GAO-05-646R 

16

Arrest Offenses

Illegal aliens in our study population were arrested for almost 700,000 

offenses, averaging 13 offenses per illegal alien.a

• Number of illegal aliens in our study 

population 55,322

• Total number of arrestsb 459,614

• Total number of criminal offenses 691,890

• Average number of criminal offenses 

per illegal alien 13

• Median number of criminal offenses

per illegal alien 10

aOne arrest incident may include multiple offenses. 

bFor the study population of illegal aliens, the analysis time frame covers arrests recorded in the FBI’s IAFIS—dating from 1947 to October 28, 2004.

Source: GAO analysis of FBI IAFIS data.
Enclosure I: Briefing Slides 

Page 21 GAO-05-646R 

17

Number of Offenses

Ninety-eight percent of illegal aliens in our total study 

population were arrested for two or more offenses.

-

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

1 2 - 5 6 - 10 11 - 15 16 - 20 21 - 25 26 - 30 31 or greater

Number of offenses

1,084 (2%)

13,414 (24%)

15,317 (28%)

9,928 (18%)

6,314 (11%)

3,744 (7%)

2,187 (4%)

3,334 (6%)

Total number of offenses: 691,890

Number of illegal aliens in our study population: 55,322

Number of illegal aliens 

(percentage of population)

Source: GAO analysis of FBI IAFIS data.
Enclosure I: Briefing Slides 

Page 22 GAO-05-646R 

18

Arrest Offenses:

Forty-five percent of illegal alien offenses were for drugs and immigration.

Source: GAO analysis of FBI IAFIS data.

Note: Not all arrest offenses would have resulted in a prosecution, a conviction, or an incarceration.

Total 691,890 100% 267,709 100% 424,181 100%

Other 24,310 4% 9,403 4% 14,907 4%

Arson 457 <1% 173 <1% 284 <1%

Kidnapping 3,236 <1% 837 <1% 2,399 1%

Homicide 5,992 1% 1,156 <1% 4,836 1%

Property damage 6,478 1% 2,238 1% 4,240 1%

Disorderly conduct 8,768 1% 2,986 1% 5,782 1%

Sex offense 11,833 2% 2,501 1% 9,332 2%

Stolen property 13,415 2% 4,201 2% 9,214 2%

Robbery 15,305 2% 4,177 2% 11,128 3%

Motor vehicle theft 20,950 3% 6,494 2% 14,456 3%

Weapons violations 22,263 3% 7,236 3% 15,027 4%

Fraud, forgery, and counterfeiting 25,773 4% 8,564 3% 17,209 4%

Larceny/theft 31,883 5% 12,206 5% 19,677 5%

Burglary 38,689 6% 13,156 5% 25,533 6%

Obstruction of justice 45,632 7% 15,064 6% 30,568 7%

Assault 50,958 7% 14,908 6% 36,050 8%

Traffic violations 55,060 8% 13,290 5% 41,770 10%

Immigration 144,166 21% 84,382 32% 59,784 14%

Drugs 166,722 24% 64,737 24% 101,985 24%

Number Percent Number Percent Number Percent 

Offenses for illegal aliens in 

state prisons and local jails

Offenses for illegal aliens in 

Total offenses federal prisons

Criminal offense
Enclosure I: Briefing Slides 

Page 23 GAO-05-646R 

19

Convictions: Federal Prison Illegal Alien Inmates

Almost 90 percent of this portion of our study population was convicted 

of immigration or drug offenses.

1These offenses are for the inmates in our study population incarcerated as of December 27, 2003. 

Note: The Bureau of Prison (BOP) records the offense resulting in the longest sentence.

Source: GAO analysis of BOP data.

Totals 18,581 100.0%

Other 62 <1%

Homicide 13 <1%

Court, corrections 25 <1%

Kidnapping 26 <1%

Robbery 28 <1%

Assault 41 <1%

Burglary, larceny, property crimes 95 1%

Fraud, bribery, extortion 185 1%

Weapons, explosives, arson 251 1%

Unknown 1,183 6%

Drugs 3,978 21%

Immigration 12,694 68%

Offense Number Percent 
Enclosure I: Briefing Slides 

Page 24 GAO-05-646R 

20

Location of Arrests: Illegal Aliens In Our Study Population

Eighty percent of all arrests occurred in three states–California, Texas, 

and Arizona.

Colorado

2%

Oregon

1%

Utah

1%

Georgia

1%

Illinois

1%

Nevada

1%

Remaining 39 States, 

District of Colombia, 

and U.S. Territories

7%

New York

2%

Washington

3%

Arizona

8%

Texas

14%

California

Total number of illegal aliens in our study population: 55,322

Total number of arrests: 459,614

Note: The remaining 39 states, the District of Columbia, and the U.S. territories represent less than 1 percent each. U.S. territories include the Virgin Islands, 

Puerto Rico, and Guam. The percentage totals do not add to 100 because of rounding.

Source: GAO analysis of FBI IAFIS data.

58%
Enclosure I: Briefing Slides 

Page 25 GAO-05-646R 

21

Location of Arrests: Federal Prison Illegal Alien Inmates

Seventy-one percent of all arrests occurred in three states–California, 

Texas, and Arizona.

California

Texas

20%

Arizona

9%

Washington

4% Oregon

2%

Remaining 41 states, 

District Of Columbia, 

and U.S. territories 

15%

Illinois

2%

New York

2%

Colorado

2%

Utah

2%

Note: The following 9 states represent approximately 1 percent each: Florida, Georgia, Pennsylvania, Nevada, New Mexico, Minnesota, Louisiana, 

Nebraska, and Kansas. The remaining 32 states, the District of Columbia, and the U.S. territories represent less than 1 percent each. U.S. territories 

include the Virgin Islands, Puerto Rico, and Guam. 

Source: GAO analysis of FBI IAFIS data.

Total number of illegal aliens in our study population: 18,581

Total number of arrests: 185,168

42%
Enclosure I: Briefing Slides 

Page 26 GAO-05-646R 

22

Location of Arrests: State Prison and Local Jail Illegal Alien Inmates

Eighty-seven percent of all arrests occurred in three states–California, 

Texas, and Arizona.

Colorado

2 %

Nevada

1 %

G e org ia

1 % Oregon

1 %

Remaining 41 

S ta tes , D istric t O f 

C olum b ia, an d U .S . 

Territories 

4 %

New York

2 %

W ashington

2 %

A riz on a

8 %

Texas

10%

C a liforn ia

Total number of illegal aliens in our study population: 36,741

Total number of arrests: 274,446

Note: The remaining 41 states, the District of Columbia, and the U.S. territories represent less than 1 percent each. U.S. territories include the Virgin 

Islands, Puerto Rico, and Guam.

Source: GAO analysis of FBI IAFIS data.

69%
Enclosure II: Objectives, Scope, and 

Methodology 

Page 27 GAO-05-646R 

Using data we had obtained for our report, Information on Criminal 

Aliens Incarcerated in Federal and State Prisons and Local Jails, 

GAO-05-337R, we selected our study population of aliens that illegally 

entered the United States using the following methodology. We started 

with data we obtained from the Federal Bureau of Prisons (BOP) on the 

population of aliens incarcerated in federal prison as of December 27, 

2003. We added to this the population of convicted criminal aliens 

incarcerated in state prisons and local jails between July 1, 2002, and June 

30, 2003 for whom state and local governments sought reimbursement 

under the State Criminal Alien Assistance Program (SCAAP).1

 These two 

populations were chosen because they were the latest population data we 

had when we began our analysis. From this combined population we 

identified those criminal aliens that had both an alien identification 

number and an FBI identification number in the data records we obtained. 

An alien identification number is a unique number assigned to an alien 

who has come into contact with immigration authorities. The FBI 

identification number is a unique identifier the FBI assigns to a set of 

fingerprints that allows linking relevant records of arrests and any 

subsequent activity within the criminal justice system. We needed to have 

alien identification numbers in order to be able to identify those aliens 

illegally in the United States and FBI numbers in order to obtain the 

relevant criminal history record information from the FBI. For those 

criminal aliens with both an alien identification number and an FBI 

identification number, we requested that the U.S. Immigration and 

Customs Enforcement (ICE) within the Department of Homeland Security 

identify those aliens that, according to their records, had entered the 

country illegally. For those aliens that ICE identified as having entered the 

country illegally, we provided the FBI number and other identifying 

information to the FBI and requested their criminal history records. The 

criminal history record for each unique FBI identification number 

contained the dates of each arrest, the arresting agency, an offense code,2

and a literal description of each offense for which the alien was arrested, 

e.g., drug possession, burglary, robbery. The arrest information for each 

illegal alien is all arrests recorded in IAFIS as of October 28, 2004. Table 1 

describes the number of criminal aliens at each level of our analysis. 

 1

The Department of Justice Bureau of Justice Assistance (BJA) program that reimburses 

state and local governments for a portion of their costs of incarcerating some, but not all, 

criminal aliens illegally in the country. 

2

A numeric code that the arresting law enforcement agency assigns to the criminal offense. 

Enclosure II: Objectives, Scope, and 

Methodology 
Enclosure II: Objectives, Scope, and 

Methodology 

Page 28 GAO-05-646R 

Table 1: Selection of Illegal Alien Study Population Used For Our Analysis 

Inmates incarcerated in federal

prison on December 27, 2003

Inmates incarcerated by state 

prisons and local jails between 

July 1, 2002, and June 30, 2003, 

and submitted to SCAAP for 

reimbursement

Number of convicted criminal aliens 46,063 262,105

Number of unique convicted criminal aliens with a FBI 

identification number and an alien identification 

number 

36,390 59,427

Number of the above unique convicted criminal aliens 

that ICE determined to have entered illegally 

18,581 36,741

Total population of illegal aliens used in our analysis 55,322 

Source: GAO 

To determine the number of arrests for our study population of illegal 

aliens, we totaled the number of unique dates of arrest for each unique FBI 

number contained in the FBI criminal history records we obtained. The 

earliest arrest record was in 1947, the latest October 28, 2004. The criminal 

history records contained several hundred thousand different literal 

descriptions of arrest offenses. To determine the offenses for which these 

illegal aliens were arrested, we categorized the arrest descriptions 

contained in the criminal history records into 1 of 19 major offense 

categories (e.g., immigration, drugs) using FBI guidance to law 

enforcement agencies on how to categorize different types of crimes. FBI 

officials concurred with the way we categorized the literal descriptions 

into the 19 major offense categories. To identify the states these illegal 

aliens were arrested in, we analyzed the data contained in the arresting 

agency field of the criminal history record for each unique date of arrest. 

We determined that the BOP data are sufficiently reliable for the purposes 

of this report. To assess the reliability of the data, we discussed with 

responsible BOP officials how data on the number of federal inmates and 

whether they are a citizen or an alien are collected and maintained in 

BOP’s inmate tracking system called SENTRY. We reviewed BOP policies 

and procedures related to entering data into the SENTRY system and 

reviewed a Department of Justice Inspector General review of the 

SENTRY system. 

We determined that SCAAP data are sufficiently reliable for the purposes 

of this report. To assess the reliability of the SCAAP data, we discussed 

with responsible BJA officials how data on criminal aliens reimbursed 

Data Reliability 
Enclosure II: Objectives, Scope, and 

Methodology 

Page 29 GAO-05-646R 

through SCAAP are collected and maintained. We reviewed BJA SCAAP 

policies and procedures and guidance on how state and local jurisdictions 

can apply for reimbursement under the program. State and local 

jurisdictions submit inmates to BJA for reimbursement based on the 

inmates’ self-reporting their country of citizenship or place of birth. The 

state and local jurisdictions certify they have exercised due diligence in 

determining which inmates qualify for reimbursement and the inmates’ 

data, such as name and if available, alien identification and FBI 

identification numbers. 

We determined that ICE data are sufficiently reliable for the purposes of 

this report. To assess the reliability of ICE’s determination that aliens with 

both an alien identification number and an FBI identification number had 

entered illegally, we discussed with the ICE official who conducted the 

analysis the process he used to make this determination. The 

determination was made after querying several immigration databases 

using the unique alien identification number we had supplied. 

We determined that the FBI’s IAFIS data on arrests are sufficiently reliable 

for the purposes of this report. To assess the reliability of the data, we 

discussed with responsible FBI officials how data on arrests are collected 

and maintained in IAFIS. We reviewed FBI policies and procedures related 

to entering data into the FBI system. The FBI estimates 8 percent of the 

criminal arrests are no longer maintained by the FBI because 7 states, 

Colorado, Florida, Montana, Oklahoma, Oregon, New Jersey, and North 

Carolina only report their first arrest to the FBI. 

We performed our work from October 2004 through May 2005 in 

accordance with generally accepted government auditing standards. 

(440407) 
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