Update: Most Terrorist Incidents in the Past Five Years Committed by Foreign-Born Individuals

According to the Terrorist Screening Center, 98 percent of the approximately 550,000 individuals on the terrorist watchlist are foreign-born. Roughly 10,000 to 20,000 on the watchlist reside within the United States. It is therefore not surprising that four of the 13 most notorious terrorism arrests since 2009 involved naturalized U.S. citizens. Five cases involved native-born U.S. citizens, while eight involved foreign nationals (it appears the Boston Marathon bombing included two foreign-born brothers), all of whom had received multiple U.S. immigration benefits. What follows is not a comprehensive list, but it does reflect the most significant U.S.-based terrorist incidents since 2009.

Illegal Overstays

February 2012: Amine el-Khalifi, a 29-year-old Moroccan man arrested for an attempted suicide bombing two blocks from the Capitol building while exiting the parking garage at the Labor Department. He thought he had a suicide bomb vest and an automatic weapon. He had been living in the United States since he was 16 as an illegal immigrant, having overstayed his tourist visa.

September 2009: Hosam Smadi, a 19-year Jordanian illegal overstay by a year, attempted to detonate what he thought was a car bomb to destroy a 1.2 million-square-foot, 60-story Dallas office building.

Multi-Entry Visa

December 2009: Umar Farouq Abdulmutallab, a Nigerian with a multi-entry visa to the United States and prior travel into the country for a religious conference, detonated a malfunctioning explosive on board an international flight about to land in Detroit on Christmas Day.

Legal Permanent Residents

April 2013: Tamerlan Tsarnaev, 26, the alleged bomber of the Boston Marathon who was killed during a manhunt during the early morning hours of April 19, and his brother Dzhokhar Tsarnaev (see below), are believed to have used two homemade bombs that killed three and injured about 175 individuals aged five to 78. Both had come to the United States 10 years ago from Chechnya as refugees. Tamerlan was reportedly a legal permanent resident. U.S. law requires asylum and refugee applicants to apply for legal permanent residence within one year of arrival.

September 2009: Najibullah Zazi, an Afghan legal permanent resident residing in the United States since 1999, conspired to conduct suicide bombings (with others) on four rush-hour New York City subway lines on or near the 9/11 anniversary. The conspiracy had operational support from Al Qaeda abroad and explosives materials were stockpiled.

U.S. Citizens (Naturalized)

April 2013: April 2013: Dzhokhar Tsarnaev, 19, reportedly a naturalized citizen who conspired with his brother, Tamerlan Tsarnaev (see above), to bomb the Boston Marathon. He is currently on the run from the authorities.

November 2010: Mohamed Osman Mohamud, a 19-year-old Somali-born U.S. citizen, attempted to detonate what he thought was a car bomb during a Christmas tree lighting ceremony in Portland, Ore. He had told undercover agents he had dreamed since he was 15 of a "spectacular fireworks show" where he hoped all would be dead or wounded.

October 2010: Farooque Ahmed, a Pakistani-born immigrant who grew up on Staten Island and became a U.S. citizen at 17, conspired to bomb four Metro subway stations near the Pentagon in Virginia — Arlington Cemetery, Pentagon City Mall, Crystal City, and Court House — and a Washington, DC, hotel. Ahmed had conducted extensive surveillance and drawn up plans.

May 2010: Faisal Shahzad, a Pakistani-born U.S. citizen, detonated a "vehicle-borne explosive device" that malfunctioned in Times Square. He came to the United States in 1997 (likely on a tourist visa), but did not acquire a student F-1 visa until 1998. In 2002, he acquired an H-1B worker visa. In 2004, in an arranged marriage in Pakistan, he wed a U.S. citizen of Pakistani descent. In 2006, he became a legal permanent resident and in April 2009, just before the terrorist attempt, he acquired citizenship. His American passport enabled him to attempt to flee the country in May without concern of jeopardizing his legal status or calling attention to himself while his naturalization application was still pending.

U.S. Citizens (Native-Born)

December 2010: Antonio Martinez, an Islamic convert, attempted to detonate what he thought was a car bomb in front of a military recruiting center near Baltimore, Md.

November 2009: Nidal Malik Hasan, born to Jordanian immigrants of Palestinian descent, killed 13 soldiers and wounded 43 others in a shooting spree at Fort Hood, Texas.

October 2009: David Coleman Headley, of Pakistani descent, was arrested as a surveillance accomplice for the 2008 Mumbai (Bombay) terrorist attacks that killed over 160 people.

September 2009: Michael Finton, an Islamic convert, attempted to detonate what he thought was a car bomb in front of a federal government building in Springfield, Ill.

June 2009: Carlos Bledsoe, an Islamic convert, killed one soldier and wounded another at a military recruiting station in Little Rock, Ark.

* * *

In 2010, the FBI's Terrorist Screening Center confirmed the identity of 4,876 alleged terrorists who had encounters — usually for reasons unrelated to terrorism — with law enforcement.

For the full CIS Memorandum detailing the fact that 98 percent of the terrorist watchlist, which also includes Americans, are foreign-born individuals, see "Administrative Amnesty and the Thousands of Watchlisted Terrorists Residing in the United States".

NOTE: This posting was updated on April 24, 2013.