Terrorism and Immigration

A total of 230 foreign‐​born terrorists were responsible for 3,046 murders on US soil from 1975 through the end of 2023. The chance of a person perishing in a terrorist attack committed by a foreigner on US soil over that 49‐​year period was about 1 in 4.5 million per year. The hazard posed by foreigners who entered in different ways varies considerably. For instance, the annual chance of being murdered in an attack committed by an illegal immigrant was zero.

The federal government has an important role in screening foreigners who enter the United States and excluding those who pose a threat to the national security, safety, or health of Americans, as foreign‐​born terrorists explicitly do. This policy analysis does not make predictions about foreign‐​born terrorism on US soil; it merely analyzes the past risk posed by foreign‐​born terrorists on American soil. The past is the only source of data and information available about foreign‐​born terrorists on US soil, but foreign‐​born‐​terrorist trends could change, and there is no guarantee that past trends will continue. Still, the data and information in this focused terrorism risk analysis can aid in the efficient allocation of scarce government resources to best counter the small threat of foreign‐​born terrorists.

The federal government’s security resources should be allocated to the most efficient means of reducing the costs of terrorism. In the years after the 9/11 terrorist attacks, the government initially applied cost‐​benefit methods for evaluating the risk of terrorism, the cost of terrorism, and the supposed security benefits provided by the Department of Homeland Security. However, those methods were not well developed because cost‐​benefit analyses are anathema to decisionmakers at most government agencies, who are inclined to assume that the benefits provided by their agencies offset high costs.¹ As a partial remedy to that long‐​running deficiency, the Strategic National Risk Assessment seeks to evaluate the risk of threats and hazards to help the government more effectively allocate resources to the security threats that pose the greatest risk.² Even so, the assessment does not include a thorough terrorism risk analysis of different visa categories or distinguish native‐​born terrorists from those born abroad. Substantial administrative hurdles and barriers are in place to block foreign‐​born‐​terrorist infiltration from abroad through vigorous vetting procedures that have low error rates.³ Any change in immigration policy for terrorism prevention should be subject to a cost‐​benefit calculation. Sensible terrorism screening policy must do more good than harm to justify its existence, meaning that the cost of the damage the policy prevents should at least equal the cost it imposes.

This paper identifies 230 foreign‐​born terrorists in the United States who killed 3,046 people in attacks on US soil from January 1, 1975, to December 31, 2023. Nine of them entered the United States as illegal immigrants; 79 were lawful permanent residents; 24 were students; 1 entered on a K‑1 fiancé(e) visa; 29 were refugees; 13 were asylum seekers; 43 were tourists on various visas; 15 were from Visa Waiver Program countries; 1 entered on an A‑2 visa for government business or military training; and 1 was on an H‑1B visa for skilled temporary foreign workers. The visas for the remaining 15 terrorists could not be determined and are recorded as “unknown.” During that period, the chance of being murdered by a foreign‐​born terrorist on US soil was 1 in 4,449,257 a year. The annual chance of being murdered by someone other than a foreign‐​born terrorist in a normal homicide was more than 323 times greater than the chance of dying in a foreign‐​born terrorist’s attack.

This policy analysis is an update and simplification of three previous Cato policy analyses on the same topic that were published in 2016, 2019, and 2023. It differs from the 2016 and 2019 editions because it does not include the total number of visas issued during the years analyzed, does not include a cost‐​benefit analysis of different immigration policies intended to reduce the threat of foreign‐​born terrorism, and it further differs from the 2019 version because it does not include native‐​born terrorists.

The risks of foreign‐​born terrorists on US soil are quantified by evaluating how many people they murdered and injured in attacks, the ideologies of the attackers, the visas on which the foreign‐​born terrorists entered the country, their countries of origin, and the costs of their terrorist attacks.

Few researchers have tried to identify the specific visas used by terrorists and, with the exception of the earlier versions of this policy analysis, no others have used that information to produce a risk assessment for each US visa category or by nationality.⁴ John Mueller and Mark Stewart produced superb terrorism risk analyses but did not focus on the terrorism risks broken down by visa category or nativity from immediately after 9/11 through early 2015.⁵ Robert S. Leiken and Steven Brooke wrote the most complete survey of visas used by foreign‐​born terrorists.⁶ However, their published work does not separate threats by country, and their analysis ended in 2006; in addition, their data set is no longer available, and they did not produce a risk analysis.⁷ The US Government Accountability Office found that immigrants are overrepresented among those convicted of terrorist‐​related offenses post‑9/​11.⁸ Other scholars have analyzed the broader links between immigration and terrorism but have not produced risk analyses.⁹

Terrorism is the threatened or actual use of illegal force and violence by a nonstate actor to attain a political, economic, religious, or social goal through coercion, fear, or intimidation.¹⁰ This analysis focuses on terrorism during the 49‐​year period from January 1, 1975, to December 31, 2023, which began with large waves of Cuban and Vietnamese refugees entering the country—a potential terrorism risk—and ended with Turkish student Tibet Ergul firebombing an abortion clinic.¹¹ It identifies foreign‐​born terrorists who were convicted of planning, attempting, or committing a terrorist attack on US soil and links them with the specific visa they were first issued, as well as the number of people, if any, each of them murdered in their attacks; the number of people, if any, they injured; the countries where they were born; and the ideologies to which they subscribed (for simplification, illegal immigrants are included in a visa category called “illegal”). This report counts terrorists who were discovered trying to enter the United States on a forged passport or visa as illegal immigrants. Foreigners who were arrested at a port of entry while trying to legally enter the United States are counted against the visa they tried to use even if they were inadmissible. Asylum seekers usually arrive on a different visa with the intent of applying for asylum once they arrive, so they are counted under the asylum category unless they entered months before claiming asylum. For instance, the Tsarnaev brothers, who carried out the Boston Marathon bombing on April 15, 2013, traveled here on tourist visas from Kyrgyzstan but are categorized as asylum seekers because their family, as ethnic Chechens living in Russia who feared state persecution, immediately applied for asylum.¹²

Next, information on individual terrorists, their visa types, and the number of casualties they caused is compared with the monetized loss per casualty to quantify the loss. The monetized loss per casualty is based on an economic concept called the value of a statistical life, which reflects the societal willingness to pay for risk reductions that prevent one statistical death in the aggregate. Crucially, this does not assign a value to a specific individual’s life. Where conflicting numerical estimates exist, the highest plausible figures are used to maximize the risks and costs of terrorism in terms of human life. The Appendix lists all the foreign‐​born terrorists identified by relevant date of attack or arrest, number of murders, number of injuries, visa type, country of birth, and ideology.

Finally, other costs of terrorism, such as injuries, property damage, losses to businesses, and reduced economic growth, are briefly considered. It is easy to draw comparisons between attacks regarding fatalities, but injuries are inherently difficult to compare because of their wide spectrum of severity. The number of injuries is therefore the least meaningful statistic and the judicious reader should interpret it with caution. Only three terrorist attacks committed by foreigners on US soil created significant property and business damage, as well as wider economic damage: the 1993 World Trade Center bombing, the 9/11 attacks, and the Boston Marathon bombing. The costs of the government’s responses to terrorism, such as foreign wars and domestic counterterrorism spending, are excluded. This analysis is concerned primarily with the cost of human lives taken in terrorist attacks and considers the costs of injuries and property damage in subsequent sections.

This policy analysis examines foreign‐​born terrorists and thus excludes American‐​born terrorists. For attacks that were planned or carried out by native‐​born Americans in concert with foreign‐​born terrorists, the latter are credited entirely for the murders and injuries that resulted from the plot. This analytical choice increases the estimates of harm caused by foreign‐​born terrorists. For plots that included many foreign‐​born terrorists and victims, the number of victims is divided equally between the terrorists in each attack. For instance, the 1993 World Trade Center attack was committed by six foreign‐​born terrorists. Six people were murdered and 1,042 people were injured, making each terrorist responsible for 1 murder and 173.67 injuries. Airplane hijackings that started but did not end in the United States, such as the September 10, 1976, hijacking of TWA Flight 355 out of New York’s LaGuardia Airport by Croatian nationalists that eventually ended in Paris, are also included. However, this analysis excludes terrorist attacks in which the identities of the perpetrators are unknown, as well as attacks that occurred or were intended to occur (but were not successfully carried out) abroad. Those innocent people killed or injured by the police or security forces responding directly to a terrorist attack are counted as victims of the terrorist attacks. Terrorists are included if they made terroristic threats combined with an actual effort to commit the attack, purchased or acquired illegal firearms, had bombmaking experience or equipment, or if through a hoax they made it appear as if they had committed the attack.

Moreover, those who committed violent crimes domestically to fund terrorism on US soil, even if they never committed the actual terrorist attack, are counted as terrorists. Terrorists who were planning an attack from overseas but were killed or died before entering the United States are not counted. Convictions for weapons charges are not delineated as terrorism unless the weapons were bombs, dynamite, or poisons, and their use was combined with terroristic threats. Mere possession of machine guns or other illegal firearms is not terrorism. People who teach others how to build a bomb are not counted as terrorists, nor are those who solicit others to commit terrorist attacks, nor those who lie to law enforcement officers on behalf of their friends, family, or acquaintances who are terrorists. Lastly, terrorists who were entrapped by the FBI are counted.¹³

The ideologies of foreign‐​born terrorists are broken into the following categories:

• Islamism,
• Foreign nationalism,
• Right‐​wing (including members of the involuntarily celibate ideology, anti‐​abortion, etc.),
• Religious (non‐​Islamist),
• Left‐​wing (communism, animal rights, environmentalism, etc.),
• Separatism of various kinds; against specific religions (such as anti‐​Jewish or anti‐​Muslim), and
• Unknown or other.

The citizenship of terrorists is their country of origin at their birth. The most difficult challenge is distinguishing terrorism from so‐​called hate crimes motivated by ethnic, racial, national, religious, or other forms of bigotry.¹⁴

Finally, calculating the risk of being murdered in a foreign‐​born‐​terrorist attack on US soil partly depends on the number of people in the United States. The US Census Bureau and the American Community Survey record only the resident population for any year, but at any given time there are many temporary travelers and tourists within the United States. Ideally, these individuals should be included in any risk calculation because they could also be murdered or injured in a terror attack. However, the previous versions of this policy analysis did not include them in the denominator for the risk calculations. This may seem like a small point, but, considering there are several million tourists in the United States at any given time, their inclusion in the risk calculation would lower the estimated chance of being murdered or injured in a terrorist attack for each year. Notably, Uzbek‐​born Sayfullo Habibullaevic Saipov murdered eight people in a terrorist attack in New York City on Halloween 2017, and five of his victims were Argentinian tourists.¹⁵ Undoubtedly, some of the people murdered or injured in other attacks have also been tourists or other nonresidents. Despite this, estimating the number of tourists in the United States at any given time over the last 49 years would require too many assumptions and estimates to be statistically reliable. Therefore, this policy analysis counts all people murdered or injured in terrorist attacks on US soil, but counts only residents as the population for estimating the annual chance of being murdered in an attack. This methodological choice overestimates the risk of dying or being injured in a terrorist attack.

The 2019 policy analysis included information on native‐​born terrorists, their victims, their ideologies, and other characteristics. Counts of native‐​born terrorists are not included in this version for four main reasons. First, the collection and categorization of native‐​born American terrorists back to 1975 is costly. Second, no readers of the 2019 policy analysis remarked on the native‐​born‐​terrorist numbers; their attention was focused almost exclusively on foreign‐​born terrorists. Third, the data on native‐​born terrorists would not be as reliable as the data for foreign‐​born terrorists. The 2020 riots following the murder of George Floyd and the January 6, 2021, rioters who attempted to disrupt the count of electoral votes to certify Joe Biden’s election present complex methodological challenges. In both cases, some of the rioters undoubtedly committed violence for political purposes but many did not. Identifying the thousands of people involved in both sets of riots, separating property criminals and other hooligans from those who intended political violence, and uncovering their immigration statuses would be too difficult and involve too many ad hoc decisions by the author. However, not including the violence from those two politically inspired spasms of disorder would also give an incomplete view of native‐​born‐​terrorist incidents, since almost all perpetrators in the George Floyd and January 6 riots were native‐​born Americans.¹⁶ Fourth, wide segments of the public disagree on whether the riots in 2020 and 2021 would rise to the level of terrorism that is analyzed in this paper, whereas there is little disagreement over whether the incidents that are included here, such as the 9/11 attacks, were terrorism.

The terrorists’ identities come from 18 main data sets and documents. The first is Terrorism since 9/11: The American Cases, edited by John Mueller.¹⁷ This voluminous work contains biographical and other information related to terrorist attacks and cases since September 11, 2001. Mueller’s work is indispensable because he focuses on actual terrorism cases rather than questionable instances of people who were investigated for terrorism, then cleared of terrorism and convicted under nonterrorism statutes, but whose convictions the government ultimately counted as “terrorism‐​related.” For instance, a 2017 Department of Justice National Security Division’s “Chart of Public/​Unsealed International Terrorism and Terrorism‐​Related Convictions from 9/11/01–12/31/15” included 627 terrorism‐​related convictions, of which only 280, or 45 percent, were convicted under an actual terrorism statute.¹⁸ Seventy of those 280 convictions were for planning or executing an attack on US soil, and only 40 of the 70 people were foreign‐​born. Many of those terrorism‐​related convictions were for citizenship fraud, passport fraud, or false statements to an immigration officer by immigrants who never posed an actual terrorism threat to the homeland. The convictions of Nasser Abuali, Hussein Abuali, and Rabi Ahmed provide further context for the government’s use of the term “terrorism‐​related.” An informant told the FBI that the trio tried to purchase a rocket‐​propelled grenade launcher, but the FBI found no evidence supporting the accusation. The three individuals were instead charged with, and convicted of, receiving two truckloads of stolen cereal.¹⁹ The government classified their convictions as terrorism‐​related despite the lack of a terrorist connection, terror threat, planned attack, conspiracy, or any tentative steps toward the execution of a terror attack. As a result, Nasser Abuali, Hussein Abuali, and Rabi Ahmed are not included in this analysis. While this incident is especially absurd, it is similar to many of the other 346 terrorism‐​related convictions in the Department of Justice report.

The second source is the Fordham University Center on National Security’s terrorism trial report cards, a compilation of all the trials for terrorism cases for Islamic State of Iraq and Syria (ISIS) members in the United States as well as statistical analyses and overviews.²⁰

Third are the 2010 and 2013 Congressional Research Service reports, “American Jihadist Terrorism: Combating a Complex Threat.”²¹

The fourth source of terrorist identities is a combination of the RAND Corporation’s Database of Worldwide Terrorism Incidents (RDWTI), which covers the years 1968–2009, and other RAND publications on terrorism.²²

Fifth is the Global Terrorism Database (GTD) maintained by the National Consortium for the Study of Terrorism and Responses to Terrorism at the University of Maryland, College Park, and other research produced by the GTD.²³ It is important to highlight that the RDWTI and GTD overlap considerably, which provides a valuable check.

Sixth are the results of numerous Freedom of Information Act requests by various organizations and individuals asking for all terrorism‐​related convictions since 9/11.²⁴

Sources 7 through 17 are the New America Foundation; The Intercept; the Investigative Project on Terrorism; the research of University of North Carolina sociology professor Charles Kurzman; the George Washington University Program on Extremism; the Center for Immigration Studies; the Southern Poverty Law Center; research by the National White Collar Crime Center; the Terrorism Research Center at the Fulbright College of Arts and Sciences at the University of Arkansas; a dissertation by Catlyn Kenna Keenan; numerous FBI reports from 1982 to 2005 on terrorist incidents in the United States; and press releases, statements, or speeches issued by the Department of Justice.²⁵

Individual immigration information for the terrorists, their ideologies, and their countries of origin comes from the sources mentioned above, as well as news stories, court documents, and other government reports. Many of the foreign‐​born terrorists analyzed here entered the United States on one visa but committed their terrorist attack after they switched to another visa, were naturalized, or lost immigration status. This report classifies those foreign‐​born terrorists under the visa they had when they initially entered the country. The only exception is for asylum seekers, who are counted under the asylum visa category. That exception is important because those individuals usually make their claim at the US border or after they have entered on another visa, often with the intention of applying for asylum. As an example of the general methodology, Faisal Shahzad is counted on the student visa because he initially entered on that visa and then obtained an H‑1B visa before his unsuccessful attempt at setting off a car bomb in Times Square in 2010.

This policy analysis includes corrections and updates to previous versions based on subsequent research. It reclassifies the specific terrorist motivations for Billy Alexander, Glossy Bruce Joseph, and Manssor Arbabsiar. Previously, their attacks were all classified as political assassinations. This version of the policy analysis retires political assassination as a motivating ideology and credits Alexander and Joseph with a foreign‐​nationalism motivation and Arbabsiar with the motivation of Islamism. Earlier versions listed Nosair El Sayyid’s visa as “unknown,” but subsequent research revealed that he entered as a lawful permanent resident.²⁶

These data sets identify 230 foreign‐​born terrorists in the United States from 1975 to the end of 2023, of which 9 were illegal immigrants; 79 were lawful permanent residents; 24 were students; 1 entered on a K‑1 fiancé(e) visa; 29 were refugees; 13 were asylum seekers; 43 were tourists on various visas; 15 were from Visa Waiver Program countries; 1 was on an H‑1B visa; and 1 was on an A‑2 visa for government business or military training. The visas for 15 terrorists could not be determined.

The number of murder victims per terrorist attack comes primarily from government reports, the RDWTI, the GTD, John Mueller’s research, and media reports. From 1975 through 2023, those 230 foreign‐​born terrorists murdered 3,046 people, 97.8 percent of whom were killed on September 11, 2001. The other 2.2 percent of murder victims are dispersed over the 49‐​year period, with spikes in 1993 and 2015. These spikes in victims are from the 1993 World Trade Center bombing, which killed 6 people, and the combination of two 2015 attacks—the Chattanooga, Tennessee, shooting on July 16, 2015, which killed 5 people, and the San Bernardino, California, attack on December 2, 2015, which killed 14 people.

From 1975 through 2023, the approximate annual chance that an American resident would be murdered in a terrorist attack carried out by a foreign‐​born terrorist was 1 in 4,449,257. At one end of the spectrum, foreigners on the Visa Waiver Program killed 1 American resident in a terrorist attack, resulting in a risk of about 1 in 13.6 billion per year. On the other end of the spectrum, those on other tourist visas killed 2,829.4 people, resulting in a risk of about 1 in 4.8 million a year. The approximate chance that an American would be killed in a terrorist attack committed by a refugee was 1 in 3.4 billion a year. Of the roughly 987,456 total murders committed in the United States from 1975 to the end of 2023, a total of 3,046 (or 0.31 percent) were committed by foreign‐​born terrorists in attacks.²⁷ Those risk statistics are summarized in Table 1. The annual chance of being murdered in a criminal homicide was 323 times as great as dying in an attack committed by a foreign‐​born terrorist on US soil.

The US murder rate declined from 9.7 per 100,000 in 1975 to 6.3 per 100,000 in 2023, whereas the 1975–2023 rate of murder committed by foreign‐​born terrorists was 0.023 per 100,000 per year, only spiking at 1.05 in 2001 (Figure 1). In 31 of the 49 examined years, zero Americans were killed in a domestic attack committed by foreign‐​born terrorists. In the 22 years after 9/11, only 6 years were marred by foreign‐​born terrorist attacks that resulted in one or more murders. Figure 1 shows a single perceptible blip for terrorism—the 9/11 attacks—in an otherwise flat line.

From 1975 through 2023, the 230 foreign‐​born terrorists injured 17,078 people in attacks on US soil, injuring 5.6 people for every person they murdered (Table 2). But 86.9 percent of all people injured in foreign‐​born‐​terrorist attacks—14,842—were injured on 9/11. From 1975 through 2023, the annual chance of being injured in a terrorist attack carried out by a foreign‐​born terrorist was 1 in 793,561. Illegal immigrants injured zero American residents in terrorist attacks, whereas those on tourist visas injured 1 in 905,815 a year. The approximate chance that an American would be injured in a terrorist attack committed by a refugee was 1 in 630 million a year.

In 29 of the 49 years, zero people were injured in terror attacks committed by foreign‐​born terrorists. Paul Pelosi, the husband of former House Speaker Nancy Pelosi, was attacked in his San Francisco home in 2022 by Canadian‐​born terrorist David DePape and is the last person injured in an attack committed by a foreign‐​born terrorist.²⁸ The three most injurious attacks were 9/11 (14,842 people injured); the 1993 World Trade Center attacks (1,046 people injured); and the 1984 Rajneeshee bioterror attack in The Dalles, Oregon (751 people sickened).

The foreign‐​born‐​terrorist murder rate has a single spike in 2001 and is virtually a flat line for every other year (Figure 1). The foreign‐​born‐​terrorist murder rate of 1.05 per 100,000 in 2001 is 177 times greater than the next‐​highest annual rate, 0.0059 in 2015. The statistical mode (meaning the most common number) of the annual murder rate by foreign‐​born terrorists is zero.

The 9/11 attacks killed 2,979 people (not counting the 19 hijackers). These attacks were a horrendous crime, but they were also a dramatic statistical outlier. The year 2015 was the deadliest year excluding 2001 in the period analyzed, with 19 Americans killed by foreign‐​born terrorists. Fourteen of those victims were killed in the San Bernardino attack—the second‐​deadliest attack committed by foreign‐​born terrorists on US soil during the 49‐​year period. The 9/11 attacks killed about 213 times more people than were killed in San Bernardino.

Government officials frequently remind the public that we live in a post–9/11 world, where the risk of terrorism is so extraordinarily high that it justifies enormous security expenditures and curtailments of civil rights.²⁹ The period from 1975 to September 11, 2001, had 23 murders committed by 28 foreign‐​born terrorists out of a total of 98 who planned, attempted, or successfully carried out an attack (Table 3). From September 12, 2001, to December 31, 2023, 44 people were murdered on US soil by a total of 9 foreign‐​born terrorists out of a total of 112 foreign‐​born terrorists who planned, attempted, or committed attacks.

Prior to 9/11, the chance of being murdered by a foreign‐​born terrorist was about 1 in 276.7 million per year. After 9/11, the chance of being murdered by a foreign‐​born terrorist was about 1 in 156.9 million per year. The horrendous death toll from the terrorist attacks of 9/11 overwhelms the number of deaths from other attacks. On that one day, the chance of dying in a terrorist attack was 1 in 95,659.

Before 9/11, 1,814 people were injured on US soil by a total of 25 foreign‐​born terrorists, and the chance of being injured by a foreign‐​born terrorist was about 1 in 3.5 million per year (Table 4). After 9/11, the chance of being injured by a foreign‐​born terrorist was about 1 in 15.6 million per year. It is important to repeat that the large number of injuries in the terrorist attacks of 9/11 is far greater than the number of injuries from other attacks.

Islamism is the dominant ideological motivation for foreign‐​born‐​terrorist attacks during the 49‐​year period analyzed here. Of the 230 foreign‐​born terrorists who were active from 1975 through 2023, 67 percent were Islamists. Some 16 percent were foreign nationalists, such as Armenians who murdered people in vengeance for the genocide carried out by the Turkish government or Croatians who wanted independence for their country from Yugoslavia. The rest were spread out across other ideologies (Table 5). When broken down by ideology, the number of murders committed by foreign‐​born terrorists is even more lopsided. Including the 9/11 attacks, foreign‐​born Islamist terrorists murdered 99.4 percent of all people killed in a terrorist attack on US soil. Of all people murdered by foreign‐​born terrorists, 97.8 percent died in the 9/11 attacks. The approximate annual chance of being murdered in an attack committed by a foreign‐​born Islamist was about 1 in 4.5 million per year. That chance dropped substantially to 1 in 2.3 billion per year for foreign‐​born nationalists. The distribution of injuries is similarly skewed toward Islamists, with 95.4 percent being inflicted by foreign‐​born Islamist terrorists.

Illegal‐​immigrant terrorists who crossed either a land or water border into the United States have killed or injured zero people in attacks on US soil. Nine illegal‐​immigrant terrorists have attempted to commit attacks in the United States during the 49‐​year period analyzed here. Of those nine illegal‐​immigrant terrorists, five illegally crossed the US‐​Canada border, one stowed away on a ship, and three illegally crossed the US‐​Mexico border.³⁰ The three illegal‐​immigrant terrorists who crossed the US‐​Mexico border are brothers Dritan Duka, Shain Duka, and Eljvir Duka. They were ethnic Albanians from Macedonia who illegally crossed from Mexico into the United States with their parents in 1984 when they were aged five or younger. Twenty‐​three years after they illegally crossed into the United States, all three were arrested and later convicted for a planned attack on Fort Dix, New Jersey, in 2007.³¹ The Duka brothers were “got aways,” which means that they were illegal border crossers who were directly or indirectly observed to have illegally entered the United States, weren’t apprehended while entering, and did not turn back to Mexico.³² There is no evidence that they plotted to commit a terrorist attack in the United States when they originally entered the United States. Although zero Americans have been killed or injured in attacks committed by illegal‐​immigrant terrorists, the possibility remains that an illegal immigrant who crosses the US‐​Mexico border or enters another way could commit an attack that injures or kills Americans in the future.

When regulators propose a new rule or regulation to enhance safety, they routinely estimate how much it will cost to save a single life under their proposal, which acknowledges that human life is valuable but not infinitely so.³³ Depending on the risk‐​reward tradeoff, Americans are willing to take risks that increase their chance of violent death or murder, such as enlisting in the military, living in cities that have more crime than rural areas, or driving at high speeds—actions that would be unthinkable if individuals placed infinite value on their own lives. It then stands to reason that there is a value between zero and infinity that people place on their lives. In public policy, a review of 132 federal regulatory decisions concerning public exposure to carcinogens found that regulators do not undertake action when the individual fatality risk is lower than 1 in 700,000, indicating that risks are deemed acceptable when annual fatality risk is lower than that figure.³⁴ Using a similar type of analysis for foreign‐​born terrorism will help guarantee that scarce resources are devoted to maximizing the number of lives saved relative to the costs that are incurred.

In 2010, the Department of Homeland Security produced an initial estimate that valued each life saved from an act of terrorism at $6.5 million, then doubled that value (for unclear reasons) to $13 million per life saved.³⁵ An alternative valuation by the scholars Robert W. Hahn, Randall Lutter, and W. Kip Viscusi uses data from everyday risk‐​reduction choices made by the American public to estimate that the value of a statistical life is $15 million.³⁶ This paper relies on the $15 million estimate to remove the possibility of undervaluation.

There are other costs of terrorism that should ideally be included here, such as property damage, medical care for the wounded, and disruptions to economic growth.³⁷ However, those costs are highly variable and confined to three major terrorist attacks caused by foreigners: the 1993 World Trade Center bombing, the 9/11 attacks, and the Boston Marathon bombing. The highest plausible cost estimates for those three attacks are $1 billion, $170 billion, and $25 million, respectively.³⁸ Those costs do not count the cost of the government’s reactions. The monetized cost of terrorism in terms of lives lost was greater than the value of property and other economic damages in every terrorist attack examined here, except for the 1993 World Trade Center bombing and the 9/11 attacks.

This policy analysis categorizes terrorists’ visa status using the visa under which a terrorist first entered the United States. Those who entered illegally are counted as illegal immigrants. Terrorists who entered on fraudulent passports, fraudulent visas, or on another person’s legitimate passport or visa are counted toward those categories. For example, Iyman Faris originally entered the United States from Pakistan on a student visa and a passport that belonged to another person.³⁹ While Faris applied for asylum four months later and received a green card through marriage more than a year after that, for the purposes of this report he entered on a student visa. This estimation methodology could exaggerate the number of terrorists who entered the United States with a green card, thus diminishing the relative danger of other categories. The specifics of the various visa programs will be described in their individual subsections below.

The terrorist risk for each visa category can be understood in different ways. The following sections will present the number of foreign‐​born terrorists in each visa category and the number of murders and injuries carried out by terrorists in each visa category. Multiplying the number of murders in each visa category by the $15 million cost per victim yields the estimate of the costs of terrorism during the 1975–2023 period.

As previously noted, 3,046 people were murdered by foreign‐​born terrorists in attacks in the United States from 1975 to the end of 2023. Table 6 shows the types of visas that foreign‐​born terrorists used to enter the United States and how many victims were murdered in attacks committed by terrorists on each visa. Foreign‐​born terrorists on tourist visas have killed more Americans in attacks than those on any other type of visa, followed distantly by those who entered on student visas. The 2,979 deaths from the 9/11 attacks account for all but 67 murders in foreign‐​born‐​terrorist attacks.

Those terrorist attacks cost $45.69 billion in human life over the 49‐​year period, or about $933 million per year on average as displayed in Table 7 (no discount‐​rate adjustment). Of the 230 foreign‐​born terrorists, 174 did not murder anyone in a terrorist attack. Many of them were arrested before they attacked, or else their attacks failed to take any lives. However, they did injure 834 people in their attacks. On average, each terrorist killed about 13 people, for a total human cost of $197.8 million, and injured about 74 people.

Only 56 of the 230 foreign‐​born terrorists killed anyone in an attack. Of those terrorists, each one killed an average of 54.4 people, for a cost of $815.9 million in human life. Prior to 9/11, only two terrorists, Mir Aimal Kasi (also known as Mir Aimal Kansi) from Pakistan and Eduardo Arocena from Cuba, killed more than one person each: Mir Aimal Kasi shot and killed CIA employees Frank Darling and Lansing Bennett as they were waiting in traffic outside CIA headquarters in Langley, Virginia, on January 25, 1993; Eduardo Arocena assassinated Eulalio José Negrín on November 25, 1979, and Félix García on September 11, 1980. Over time, the number of terrorists per year has shrunk but their individual deadliness has increased.

There were 9 successful terrorists after 9/11; they killed 44 people, with each terrorist being responsible for an average of about 5 murders. Egyptian‐​born Hesham Mohamed Ali Hedayet murdered 2 people on July 4, 2002, at Los Angeles International Airport; the Tsarnaev brothers murdered 3 people at the Boston Marathon bombing on April 15, 2013, and another 2 people during their subsequent run from the law; British‐​born Elliot Oliver Robertson Rodger murdered 6 people on May 23, 2014; Kuwaiti‐​born Mohammad Youssuf Abdulazeez murdered 5 people on July 16, 2015; Pakistani‐​born Tashfeen Malik, along with her US‐​born husband, Syed Rizwan Farook, murdered 14 people on December 2, 2015, in San Bernardino, California; Sudanese‐​born Emanuel Kidega Samson murdered 1 person on September 24, 2017, in Antioch, Tennessee; Uzbek‐​born Sayfullo Habibullaevic Saipov murdered 8 people on October 31, 2017, in New York City; and Saudi‐​born Mohammed Saeed Alshamrani murdered 3 people on December 6, 2019, in Pensacola, Florida. Excluding the 9/11 attacks, each terrorist who killed at least 1 person in an attack killed an average of 1.8 people.

The injuries caused by foreign‐​born terrorists in attacks on US soil are also important to consider, although the range of monetized costs from the injuries is enormous. At the low end are minor injuries including scratches and blown‐​out ear drums, while at the high end are major injuries including brain damage, amputation, and paralysis. As a result, it is very difficult to make comparisons of injuries in different terrorist attacks. Regardless, injuries are a source of costs that terrorist attacks impose on Americans. The number of people injured by foreign‐​born terrorists in attacks in the United States from 1975 to the end of 2023 was 17,078 (Table 6); 14,842 of those injuries, or 87 percent, were inflicted during the 9/11 attacks.

The country of origin for the largest number of foreign‐​born terrorists is Saudi Arabia, which accounts for 19 of the 230 foreign‐​born terrorists from 1975 through 2023 (Table 8). Saudis were also the deadliest; combined, they murdered 2,354.8 people and injured 11,725.4 (nonwhole numbers result from dividing the number of victims of a single incident equally among multiple terrorists). There were 16 foreign‐​born terrorists from Croatia, who murdered 3 people in terrorist attacks and injured 4 during the 1970s. There were 15 foreign‐​born terrorists from Pakistan, who murdered 17 people and injured 194 in terrorist attacks on US soil. Individual terrorists from the United Arab Emirates, Saudi Arabia, Egypt, and Lebanon were the deadliest.

Terrorism presents a real threat to the life, liberty, and property of Americans. That has led many Americans to worry about foreign‐​born terrorists entering the United States, either legally or illegally, and carrying out disastrous attacks. But foreign‐​born terrorism on US soil is a low‐​probability event that poses small risks and low costs on Americans as a whole.⁴⁰ From 1975 through 2023, the average chance of dying in an attack committed by a foreign‐​born terrorist on US soil was 1 in 4,449,257 a year, and the annual chance of being injured was about 1 in 793,561. By comparison, the annual chance of being murdered by a common criminal in the United States was about 1 in 13,767 during the same time. In other words, the annual chance of being murdered in a normal homicide was about 323 times as great as dying in an attack committed by a foreign‐​born terrorist on US soil.

This policy analysis examines the past and does not project future trends in foreign‐​born terrorism, which could be quite different going forward. For instance, illegal‐​immigrant terrorists, who have hitherto murdered or injured zero people in attacks on US soil, could commit an attack in the future. Nonetheless, the past is the best guide to understanding what could happen with foreign‐​born terrorism in the coming years, and any rational analysis should start with what we know about the past before making predictions about the future.

There are several lessons for policymakers. First, relative to other risks and the absolute danger posed by foreign‐​born terrorism, the federal government likely spends too many resources on reducing the threat of foreign‐​born terrorism. Second, the threat posed by foreign‐​born terrorists is not a good reason to reduce immigration to the United States, because the costs of such a policy would exceed the benefits from the inflow of immigrants and their substantial contributions to the US economy and society. Third, illegal immigrants are not a significant terrorist threat; there were only nine terrorists who were illegal immigrants, they were arrested in the plotting stages of their planned attacks, and they killed or injured zero people over the entire 49‐​year period analyzed here. Fourth, the threat of foreign‐​born terrorism has diminished in recent years.

All identified foreign persons who attempted or committed terrorism in the United States during the 49‐​year period of 1975 through 2023 are listed in Table A1.

Nowrasteh, Alex. “Terrorism and Immigration: A Risk Analysis, 1975–2023,” Policy Analysis no. 972, Cato Institute, Washington, DC, April 9, 2024.