How Militant Islamic Terrorists Entered and Remained in the United States, 1993-2001

The Open Door

By Steven A. Camarota on May 1, 2002

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Executive Summary

The nation’s response to the horrific attacks of September 11, 2001 has taken many forms, from military action to expanded security measures at airports. As important as these measures are, there is probably no more important tool for preventing future attacks on U.S. soil than the nation’s immigration system because the current terrorist threat comes almost exclusively from individuals who arrive from abroad. The purpose of this study is to examine how foreign terrorists have entered and remained in the country in an effort to identify weaknesses in the system that can then lead to meaningful reforms. Rather than just focus on 9/11, we examine terrorism on U.S. soil over the last decade to provide a more complete picture of the threat.

While no immigration system can be completely foolproof, if only some of those involved in a terrorist plot can be stopped by our immigration system, it is possible that whatever conspiracy they are part of could be uncovered. Including the 9/11 hijackers, 48 foreign-born militant Islamic terrorists have been charged, been convicted, pled guilty, or admitted to involvement in terrorism within the United States since 1993. Almost all of these individuals are now thought to be linked to Osama bin Laden’s al Qaeda organization. This study focuses on militant Islamic terrorists because the threat they pose dwarfs that from any other terrorists, foreign or domestic. In addition to 9/11, some of the plots examined in the study include the murder of employees outside of CIA headquarters, the first attack on the World Trade Center, a plot to bomb the subway in Brooklyn, plots to bomb New York City landmarks, and the Millennium plot to bomb Los Angeles International Airport.


  • Foreign-born militant Islamic terrorists have used almost every conceivable means of entering the country. They have come as students, tourists, and business visitors. They have also been Lawful Permanent Residents (LPRs) and naturalized U.S. citizens. They have snuck across the border illegally, arrived as stowaways on ships, used false passports, and have been granted amnesty. Terrorists have even used America’s humanitarian tradition of welcoming those seeking asylum.
  • At the time they committed their crimes, 16, or one-third, of the 48 terrorists in the study were on temporary visas (primarily tourist visas), another 17 were Lawful Permanent Residents or naturalized U.S. citizens, 12, or one-fourth, were illegal aliens, and three of the 48 had applications for asylum pending. (See Table 1.)
  • Although the 9/11 hijackers entered on temporary visas, LPRs as well as naturalized U.S. citizens have played key roles in terrorism on U.S. soil. For example, Siddig Ibrahim Siddig Ali, ringleader of the plot to bomb New York City landmarks in 1993, is an LPR, and Ali Mohammed, who wrote al Qaeda’s terrorist handbook on how to operate in the West, is a naturalized U.S. citizen.
  • The nation’s humanitarian tradition of offering refuge to those fleeing persecution has also been exploited by a number of terrorists. In addition to the three terrorists who had asylum claims pending when they committed their crimes, three other terrorists, such as Gazi Ibrahim Abu Mezer, who tried to bomb the Brooklyn borough subway in 1997, used a false asylum claim to prevent deportation prior to taking part in terrorism.
  • Violations of immigration laws are very common among terrorists. Not only were 12 of the 48 terrorists illegal aliens when they committed their crimes, at least five others had lived in the country illegally at some point prior to taking part in terrorism. At least five others had committed significant violations of immigration laws prior to their taking part. For those that were illegal aliens, most entered legally on temporary visas and then overstayed. However, some snuck across the northern border, such as Abdel Hakim Tizegha, who was involved in the Millennium plot.
  • In addition to overstaying a visa, terrorists have violated immigration laws in a number of different ways. Some terrorists have engaged in fraudulent marriages to American citizens, such as Fadil Abdelgani, who took part in the plot to bomb New York City landmarks, and Khalid Abu al Dahab, who raised money and helped recruit new members for al Qaeda from within the United States.
  • Terrorists also violated immigration laws by providing false information on their applications for permanent residence, such as Sheik Omar Abdel Rahman, who inspired several terrorist plots.
  • Still other terrorists have violated the law by working illegally in the United States. At least eight terrorists held jobs for extended periods while living in the country illegally before taking part in terrorism, including those involved in the 1993 Trade Center attack, the plot to bomb New York landmarks, and the Millennium plot.
  • A lack of detention space has allowed several terrorists who had no legal right to be in the country to be released into the country. For example, Ramzi Yousef, the mastermind of the 1993 World Trade Center Attack, did not have a visa to enter the country, but he applied for asylum when he arrived at JFK airport and because of a lack of detention space he was paroled into the country.
  • Past amnesties for illegal aliens have facilitated terrorism. Mahmud Abouhalima, a leader of the 1993 Trade Center bombing, was legalized as a seasonal agricultural worker as part of the 1986 amnesty. Only after he was legalized was he able to travel outside of the country, including several trips to the Afghanistan/Pakistan border, where he received the terrorist training he used in the bombing.
  • Past amnesties have not hindered terrorism. Mohammed Salameh, another conspirator in the 1993 Trade Center bombing, applied for the same amnesty as Abouhalima and was denied. But, because there is no mechanism in place to force people who are denied permanent residency to leave the country, he continued to live and work in the United States illegally and ultimately took part in the 1993 attack.
  • Several terrorists should probably have been denied temporary visas because they had characteristics that made it likely they would overstay their visa and try to live in the United States illegally. Under Section 214(b) of immigration law, individuals who are young, unmarried, have little income, or otherwise lack strong attachment to a residence overseas are to be denied temporary visas. Several of the 9/11 hijackers, including the plot’s leader Mohammed Atta, fit these criteria.
  • The visa waiver program, which allows individuals from some countries to visit the United States without a visa, has been exploited by terrorists. French-born Zacarias Moussaoui, who may have been the intended 20th hijacker on 9/11, entered the country using the visa waiver program. Other terrorists such as Ahmed Ajaj, Ramzi Yousef, and Ahmed Ressam attempted to use false passports from visa waiver countries to enter the United States.
  • The vast majority of terrorists in the study (41 of 48) were approved for visas by an American consulate overseas prior to entering the country. Of the seven who did not have visas, three snuck into the country and four arrived at a port of entry without a visa.
  • At least two terrorists, Sheik Omar Abdel Rahman and Ali Mohammed, should have been denied visas because they were on the watch list of suspected terrorists.



Policy Recommendations

  • Because virtually every type of immigration has been exploited by terrorists, focusing on just one category such as student visas, or even temporary visas in general, would be inadequate. All aspects of our immigration system, including the way visas are processed overseas, the handling of foreign citizens at ports of entry, policing the nation’s borders, and enforcement of immigration laws within the United States need to be reformed in order to reduce the terrorist threat.
  • The fact that terrorists often disregard immigration laws means that strict enforcement of the law within the United States could significantly reduce the terrorist threat. If those who violate the law are identified and forced to leave the country, not only would it lower the risk of terrorism, it would also reduce illegal immigration, which is itself a desirable goal.
    The existence of a large illegal population (estimated at eight to nine million) creates a general contempt for the law among all parties involved, including those officials charged with enforcing it. With millions of illegal immigrants already in the country, and with immigration laws widely flouted, it is perhaps easy to understand why the immigration inspector at Miami’s airport allowed Mohammed Atta back into the country in January 2001 even though he had overstayed his visa on his last visit and had abandoned his change of status to vocational student by leaving the country.
  • Given the large number of terrorists who have lived in the United States illegally by overstaying a temporary visa, enforcing visa time limits could disrupt or perhaps even uncover future terrorist plots. The first step to enforcing time limits is the establishment of an entry-exit system that would automatically record the entry and exit of all persons to and from the United States. Those who overstay should be barred from ever entering the country again. The system would also allow the INS to identify overstayers who are still in the country. Such a system is envisioned in current legislation, and it is up to elected officials to ensure that it is properly implemented.
  • In addition to the creation of an entry-exit system, there needs to be a system to track temporary visa holders once they enter the country. Currently, a system that requires colleges and universities to inform the INS if a foreign student stops attending class or otherwise violates his visa is being implemented. This system should be expanded to include other temporary visa holders who are affiliated with American institutions such as guestworkers, intracompany transferees, and cultural exchange visitors.
  • Because several terrorists worked in the country illegally, one area of interior enforcement that might help disrupt terrorism is to enforce the ban on hiring illegal aliens by punishing employers and forcing those found working illegally to leave the country. The key step in implementing worksite enforcement would be the creation of a national computer database against which the names of all new hires could be checked.
  • Fraudulent marriages and other deceptions are also common among terrorists. The INS must do a much better job of investigating all applicants and force those who engage in fraud or deceptive behavior to leave the country.
  • Although the amount of detention space has increased in recent years, enforcement of immigration laws within the United States will require significantly more detention space. This can be accomplished both by building more INS facilities and by contracting out to jails and prisons systems that have excess capacity.
  • To make interior enforcement possible, there should be a dramatic increase in resources devoted to the enforcement of laws within the United States. At present there are only 2,000 INS agents devoted to worksite enforcement, anti-smuggling operations, and investigating fraud and document forgery. This number needs to be increased several-fold, along with administrative support staff. With many more agents the INS would be able to investigate irregularities uncovered by the employment database discussed above and allow it to investigate and expose fraudulent applicants. The student tracking system currently envisioned also requires significantly more investigators, otherwise it will not be possible to follow up reported violations.
  • In addition to interior enforcement, there needs to be a significant increase in the nation’s efforts to control the border, including a dramatic increase in the size of the border patrol and the effective deployment of barriers and sensors along the border. Attempted Brooklyn subway bomber Gazi Ibrahim Abu Mezer, who was denied a visa by an American consulate, simply went to Canada and tried to cross the border illegally. Improving visa processing while leaving the borders largely undefended is an invitation for terrorists to do just as Mezer did.
  • There must also be a dramatic increase in efforts to control the border with Mexico. While the southern border has not yet been used by terrorists, there is every reason to believe that if other means of entering the country become more difficult, and the Mexican border remains relatively easy to cross, then al Qaeda would begin to use it as an avenue to enter the United States. A large smuggling ring specializing in bringing Middle Easterners across the southern border was broken up in the late 1990s, which suggests that such a prospect is a very real possibility.
  • For visa processing overseas, greater scrutiny is needed for all visa applicants, including in-person interviews — several 9/11 hijackers were issued visas without ever even being interviewed by a consular officer. As much information as possible needs to be gathered on all applicants, including fingerprints and photos.
  • Skepticism should become the guiding principle of visa issuance. Consular officers must ask probing questions in an attempt to verify the applicant’s story, even at the risk of annoying the applicant. Top priority must be given to the protection of the American people and not the feelings of the applicant.
  • Strict enforcement of Section 214(b) of the immigration law would likely have prevented a number of terrorists from getting temporary visas, because terrorists and those who are likely to overstay their visas have much in common. Both groups tend to be young and unattached, as were at least three of the 9/11 hijackers. Section 214(b) can also be a useful tool in keeping out more senior members of al Qaeda, such as Mohammed Atta, because governments in the Middle East have suppressed extremist movements, forcing terrorists like Atta to spend most of their time abroad. This means they often have little attachment to their current residence and should therefore not be issued visas.
  • Updating the “watch list” against which the names of visa applicants are checked must be done in as timely a manner as possible, and maintaining the list must become a high priority for the State Department, INS, law enforcement, and the intelligence agencies. Current legislation mandates the integration of the watch list with other lists maintain by federal agencies, such as the FBI’s criminal database and this should be implemented as soon as possible.
  • Because governments in the Middle East have largely suppressed Islamic extremist movements, Western Europe has now become home to a significant number of terrorist organizations. This fact coupled with the availability of phony passports, means that it may be necessary to discontinue the visa waiver program and instead require all individuals from Europe to obtain a visa before visiting the United States.
  • For the Bureau of Consular Affairs, which issues visas, to perform its vital job of protecting the nation, more consular officers and support staff clearly are needed. At present there are only approximately 900 officers worldwide devoted to visa adjudication. This number must be increased dramatically so that all applicants can be carefully interviewed. Moreover, it might be necessary to separate visa adjudication from the State Department in order to insulate it from pressure to approve applicants in an effort not to alienate host governments.
  • The names of all persons entering the country at a port of entry need to be checked against the watch list every time they enter the country, even those who have visas. Published reports indicate that Khalid al Midhar, who was on the plane that hit the Pentagon, was identified as a terrorist after he received his visa but before he entered the country for a second time. Recording the name of each person when he arrives and checking names against the watch list is therefore critically important.

For the reforms suggested above to be possible, the overall level of immigration must be reduced for three reasons:

  1. Given limited governmental resources, issuing fewer permanent and temporary visas would mean greater resources could be devoted to more extensive background checks on each applicant;
  2. Fewer issuances would also mean fewer foreign-born individuals to keep track of within the United States in the future; and
  3. Reduction would give the State Department and the INS the breathing space they need to deal with their enormous processing backlogs, now over four million, as well as allow them to undertake the necessary reforms.

The primary goal of this report is to determine how terrorists have entered and remained in the country over the last decade, and also to identify problems or outright failures in the nation’s immigration system so as to make policy recommendations to correct the problems. We examine terrorists associated with al Qaeda over a 10-year period in order to discern patterns in their operations. Of course, domestic terrorist threats exist, and changes in immigration policy will have no effect on homegrown terrorism, nor will it protect Americans abroad from foreign terrorists. The existence of other threats, however, is no reason not to make every effect to prevent foreign terrorists from entering or remaining in the country. Most importantly, because of its money, organization, international reach, training, fanaticism, desire to obtain weapons of mass destruction, and willingness to inflict maximum death and destruction on civilian and military targets alike, the threat posed by Osama bin Laden’s al Qaeda network is fundamentally different from that posed by any other terrorists. It is therefore critically important that we develop immigration policies to deal with this foreign terrorist threat.

Persons Included in the Study

This report concentrates on the immigration status of Islamist terrorists at the time they committed their crimes. Including the 9/11 hijackers, 48 foreign-born militant Islamic terrorists have been charged, convicted, pled guilty, or have admitted their involvement in terrorism within the United States since 1993. Only individuals who have directed their terrorist activity at the United States and who committed at least some of their crimes on U.S. soil are included in the study. Almost all of the individuals in the study are now thought to be linked in some way to Osama bin Laden’s al Qaeda organization. Most of the terrorists included in the report, other than those killed in the 9/11 attacks, have already pled guilty or been convicted for their crimes.


Table 1



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If we are to reduce the chance of another terrorist attack, we must carefully examine how these terrorists entered and remained in the United States in the past, including attacks prior to 9/11. The findings indicate that terrorists have used almost every conceivable means of entering the country. Thus, any set of solutions must address our entire immigration system and not focus on just one part of the system.

The Immigration System is Overwhelmed. One of the main problems with the current immigration system is that the INS and State Department are simply overwhelmed by the number of applicants they must process. This fact is not in dispute. The General Accounting Office (GAO) reported in May 2001 that the receipt of new INS applications (for green cards, citizenship, temporary work permits, etc.) has increased 50 percent over the past six years and that the backlog of unresolved applications has quadrupled to nearly four million. The crush of work has created an organizational culture wherein “staff are rewarded for the timely handling of petitions rather than for careful scrutiny of their merits,” in the words of a January 2002 GAO report. The pressure to move things through the system has led to “rampant” and “pervasive” fraud, with one official estimating that 20 to 30 percent of all applications involve fraud. The GAO concludes that “the goal of providing immigration benefits in a timely manner to those who are legally entitled to them may conflict with the goal of preserving the integrity of the legal immigration system.”

Things are not much better at the State Department. Assistant Secretary of State Mary Ryan, who is in charge of visa processing, said in an November 2001 interview in the St. Petersburg Times that, “I think consular officers around the world are stretched just about as thin as they can possibly be. We do not have the personnel resources that we need to do the job the way it should be done.” Putting caps on or reducing the caps that exist for foreign students and guestworkers, and cutting permanent immigration back to the spouses and minor children of American citizens, eliminating the visa lottery, and limiting employed-based immigration to only a few highly skilled individuals would be a good start. The only way to give the State Department and the INS the breathing space they need to implement much-needed reforms is to reduce their workload. It is simply not reasonable to expect the INS in particular to deal with a constantly increasing workload, make significant process in the huge backlogs that exist, and at the same time fundamentally restructure and reform itself.

The System Does Not Have to Be Foolproof. No set of reforms will catch every terrorist every time, but the reforms outlined above will dramatically increase the chances that at least some of those involved in a large conspiracy, such as the 9/11 attacks, will be caught. This can and has before aided in the uncovering of entire conspiracies. In the case of the Millennium Plot, the apprehension of one terrorist at the border, Ahmed Ressam, caused the entire conspiracy to unravel. Reforming immigration policy can also significantly enhance national security by increasing the chance that terrorists will not be issued a visa in the first place or be able to cross the border illegally. And if they cannot enter the country, they cannot commit terrorist acts on American soil.

A Lax Immigration System Simply Cannot Be Allowed to Remain. The current immigration system does not carefully check the backgrounds and vigorously interview all visa applicants. It also does not enforce time limits on temporary visas. Fraudulent applicants for green cards are often approved and those in the country illegally are allowed to work, open bank accounts, and receive drivers licenses. Moreover, the nation’s border remains largely undefended. While such a system does not guarantee that terrorists will continue to enter and remain in the country, it certainly makes it much more likely. Greater scrutiny of visa applicants, closer tracking of the foreign citizens allowed into the country, better enforcement of immigration laws, and adequate policing of the border, coupled with the reduction in immigration that would make these reforms possible, are the kind of reasonable measures that would enhance security without infringing on the rights of Americans.


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Steven A. Camarota is the Director of Research at the Center for Immigration Studies.