T he Terrorist Screening Database (TSDB, commonly referred to as the Terrorist Watchlist) lies at the heart of federal efforts to identify and share information about identified people who may pose terrorism-related threats to the United States. It is managed by the Terrorist Screening Center (TSC) and includes biographic identifiers for those known to have or those suspected of having ties to terrorism. It stores hundreds of thousands of unique identities. Portions of the TSDB are exported to data systems in federal agencies that perform screening activities such as background checks, reviewing the records of passport and visa applicants, and official encounters with travelers at U.S. border crossings. The Federal Bureau of Investigation (FBI, the Bureau) has acknowledged that it had been investigating the shooter who killed 49 people at an Orlando nightclub on June 12, 2016. The gunman has been identified as Omar Mateen, a 29-year-old security guard in Florida who was born in New York. Reportedly, Mateen was watchlisted while under FBI investigation. This report provides background information on the watchlisting process. The TSC, a multi-agency organization administered by the FBI, maintains the TSDB. The TSC was created by Presidential Directive in 2003 in response to the terrorist attacks of September 11, 2001. Before the TSC consolidated federal watchlisting efforts, numerous separate watchlists were maintained by different federal agencies. The information in these lists was not necessarily shared or compared. The efforts that surround the federal watchlisting regimen can be divided into three broad processes centered on the TSDB: Nomination, which involves the identification of known or suspected terrorists via intelligence collection or law enforcement investigations. The U.S. government has a formal watchlist nomination process. Verification of identities for the TSDB and export of data to screening systems, which involves the creation and maintenance of the TSDB, as well as the compiling and export of special TSDB subsets for various intelligence or law enforcement end users (screeners). Screening, which involves end users—screeners—checking individuals or identities they encounter against information from the TSDB that is exported to screening databases. The No Fly List is one such database. (In FY2011, screeners reported "more than 1.2 billion queries against [the TSDB]." ) The screening process can also yield more information on particular subjects that may be fed back into the TSDB. (See Figure 1 for a visual depiction of the federal agencies involved in watchlisting.) In their daily work poring over raw information or case files, professionals at U.S. government agencies—dubbed "originators" in the watchlisting process—uncover the possible identities of people suspected of involvement in terrorist activity. Such identities can be nominated for addition to the TSDB. Originators can work in places such as intelligence and law enforcement agencies or U.S embassies and consulates. The nominations they initiate include people who are classed together in the watchlisting regimen as "known or suspected terrorists" (KSTs). For the federal government's watchlisting regimen, a "known terrorist" is an individual whom the U.S. government knows is engaged, has been engaged, or who intends to engage in terrorism and/or terrorist activity, including an individual (a) who has been charged, arrested, indicted, or convicted for a crime related to terrorism by U.S. government or foreign government authorities; or (b) identified as a terrorist or member of a designated foreign terrorist organization pursuant to statute, Executive Order, or international legal obligation pursuant to a United Nations Security Council Resolution. A "suspected terrorist" is An individual who is reasonably suspected to be, or has been, engaged in conduct constituting, in preparation for, in aid of, or related to terrorism and/or terrorist activities based on an articulable and reasonable suspicion. All nominated identities of known or suspected terrorists for the TSDB are vetted by analysts at either the National Counterterrorism Center (NCTC) or the FBI and then undergo verification at the TSC. NCTC handles the nominations of all international terrorists (including purely international suspects submitted by the FBI). In this process, NCTC maintains a classified database known as the Terrorist Identities Datamart Environment (TIDE). TIDE is the U.S. government's "central repository of information on international terrorist identities." TIDE includes: to the extent permitted by law, all information the [U.S. government] possesses related to the identities of individuals known or appropriately suspected to be or to have been involved in activities constituting, in preparation for, in aid of, or related to terrorism (with the exception of purely domestic terrorism information). In late 2013, TIDE contained the identities of approximately 1.1 million people. Of this number, about 25,000 were U.S. citizens and lawful permanent residents linked to international terrorist organizations. Not all of the entries in TIDE get into the TSDB, which according to the FBI held approximately 800,000 people in November 2014. Every day, NCTC analysts work on updating identities in TIDE, and NCTC exports a subset of its TIDE data holdings for the TSDB. Analysts at the TSC perform a final verification of identities before they become a part of the TSDB. (For more about the concepts involved, see " Making the TSDB Cut .") Finally, on its own, TIDE is an important resource used by counterterrorism professionals throughout the U.S. Intelligence Community in daily counterterrorism analytical work. FBI analysts in the Bureau's Terrorist Review and Examination Unit process FBI nominations to the TSDB. These nominations often spring from FBI investigative work. The unit forwards international nominations to NCTC for inclusion in TIDE, where the data in the nomination is reviewed before release to the TSC. The Bureau also forwards nominations of purely domestic terrorists as well as "domestic terrorists that may have connections to international terrorism" directly to the TSC for review. To make it into the TSDB, a nomination vetted by either NCTC or the FBI has (1) to meet the "reasonable suspicion watchlisting standard" and (2) have sufficient identifiers. TSC personnel verify that each nomination that makes it into the TSDB meets both of these criteria. The TSDB is a sensitive but unclassified dataset, and each record created by TSC personnel for the TSDB includes only an individual's identifiers and no "substantive derogatory information or classified national security" material. Articulable facts form the building blocks of the reasonable suspicion standard undergirding the nomination of suspected terrorists. Sometimes, on their own, the facts involved in identifying an individual as a possible terrorist are not enough to develop a solid foundation for a nomination. In such cases, investigators and intelligence analysts make rational inferences regarding potential nominees. The TSC vets all nominations, and when the facts, bound with rational inferences, hold together to form a reasonable determination that the person is suspected of having ties to terrorist activity, the person is included in the TSDB. In the nomination process, guesses or hunches alone cannot add up to reasonable suspicion. Likewise, one cannot be designated a known or suspected terrorist based solely on activity protected by the First Amendment or race, ethnicity, national origin, and religious affiliation. Once the reasonable suspicion standard is met, analysts must have the ability to distinguish a specific terrorist's identity from others. Thus, minimum biographic criteria must exist. At the very least, for inclusion in the TSDB, a record must have a last name "and at least one additional piece of identifying information (for example a first name or date of birth)." Most nominations appear to make the TSDB cut. From FY2009 to FY2013, 1.6 million individuals were nominated. About 1% (just over 14,000) were rejected. (See Figure 2 .) The TSC routinely exports watchlist information to federal agencies authorized to conduct terrorist screening. According to the TSC, this occurs as the information is processed, "seconds later, it shows up with our partners so they can do near-real-time screening.... " According to the TSC, "five major U.S. Government agencies" receive TSDB exports (subsets of the entire watchlist). Each of the agencies gets a different portion of the TSDB, "tailored to [its] mission, legal authorities, and information technology requirements." The agencies and examples of some of the screening systems that ingest TSDB information include the following: The Department of State , whose consular officers draw on TSDB information in the Consular Lookout and Support System that is used for passport and visa screening. The Transportation Security Administration , which uses information from the TSDB for aviation security screening. The No Fly List, the Selectee List, and the Expanded Selectee List are parts of what is known as the Secure Flight program. The No Fly List includes identities of individuals who may present a threat to civil aviation and national security. Listed individuals are not allowed to board a commercial aircraft "flying into, out of, over, or within United States airspace; this also includes point-to-point international flights operated by U.S. carriers." The selectee list includes individuals who must undergo additional security screening before being allowed to board a commercial aircraft. The minimum derogatory information requirements that form the basis for including an identity in the No Fly List and the Selectee List are "more stringent than the TSDB's known or reasonably suspected standard." This makes these lists much smaller than the TSDB. In 2014, there were approximately 800,000 identities in the TSDB according to the FBI, double the figure in 2008. In 2014, about 8% of the TSDB identities—around 64,000—were on the No Fly List and about 3%—roughly 24,000—were on the Selectee List. As an extra security measure developed in response to a failed attempt to trigger an explosive by a foreign terrorist on board a U.S.-bound flight on December 25, 2009, the Expanded Selectee List was created. It screens against all TSDB records that include a person's first and last name and date of birth that are not already on the No Fly or Selectee Lists. Customs and Border Protection (CBP) owns and uses TECS (not an acronym), the main system that CBP officers employ at the border and elsewhere to screen arriving travelers and determine their admissibility. TECS accepts "nearly all" records from the TSDB. CBP also uses the Automated Targeting System (ATS), which is "a decision support tool that compares traveler, cargo, and conveyance information against law enforcement, intelligence, and other enforcement data using risk-based targeting scenarios and assessments." As one of its functions, ATS "compares information about travelers and cargo arriving in, transiting through, or exiting the country, against law enforcement and intelligence databases" including information from the TSDB. As its name suggests, Automated Targeting System-Passenger (ATS-P) is the portion of ATS focused on passengers, "for the identification of potential terrorists, transnational criminals, and, in some cases, other persons who pose a higher risk of violating U.S. law" and is used by CBP personnel at the border and ports of entry as well as elsewhere. The FBI runs the National Crime Information Center's (NCIC) database, which has been described by the Bureau as "an electronic clearinghouse of crime data that can be tapped into by virtually every criminal justice agency nationwide, 24 hours a day, 365 days a year." The NCIC includes 21 files. One of them, the "Known or Appropriately Suspected Terrorist File" includes TSDB records. The NCIC database is used for domestic law enforcement screening. The Department of Defense uses TSDB information to help screen people trying to enter military bases. Employees from U.S. federal, state, and local law enforcement agencies who perform screening activities (screeners) check the identities of individuals they encounter in their daily work against specific subsets of the TSDB. Such queries happen either in-person or via submitted official (electronic or paper) forms. Examples include instances when foreign visitors and returning U.S. citizens enter the United States at a port of entry and are screened by CBP officers; state or local police regularly pull over vehicles for moving violations and interact with drivers and passengers; and foreign applicants submit visa applications which are reviewed by Department of State officials. Likely, every year, screeners make more than a billion queries against information in the TSDB. Queries that yield possible matches between the identifying information provided by individuals and TSDB holdings are known as "encounters." Screeners receive notification of possible matches via their specific screening databases. When a query produces an encounter, screeners are directed to contact the TSC. Employees in the TSC's 24-hour operations center perform additional research to track down any information that "may assist in making a conclusive identification." (Screeners only have access to the identifying information available in the TSDB, while TSC analysts can search through additional datasets and intelligence to clarify a possible match.) If a positive match is made or if the TSC analysis is inconclusive, the FBI's Terrorist Screening Operations Unit coordinates how the government responds. "For example, [the unit] may deploy agents to interview and possibly apprehend the subject." Any new information collected from an encounter is forwarded to the TSC to enhance any related existing TSDB entry. 

Summary: The Federal Bureau of Investigation (FBI, the Bureau) has acknowledged that it had been investigating the shooter who killed 49 people at an Orlando nightclub on June 12, 2016. The gunman has been identified as Omar Mateen, a 29-year-old security guard in Florida who was born in New York. Reportedly, Mateen was watchlisted while under FBI investigation. This report provides background information on the watchlisting process. The Terrorist Screening Database (TSDB, commonly referred to as the Terrorist Watchlist) lies at the heart of federal efforts to identify and share information about identified people who may pose terrorism-related threats to the United States. It is managed by the Terrorist Screening Center (TSC) and includes biographic identifiers for those known to have or those suspected of having ties to terrorism. It stores hundreds of thousands of unique identities. Portions of the TSDB are exported to data systems in federal agencies that perform screening activities such as background checks, reviewing the records of passport and visa applicants, and official encounters with travelers at U.S. border crossings. The TSC, a multi-agency organization administered by the FBI, maintains the TSDB. The TSC was created by Presidential Directive in 2003 in response to the terrorist attacks of September 11, 2001. Before the TSC consolidated federal watchlisting efforts, numerous separate watchlists were maintained by different federal agencies. The information in these lists was not necessarily shared or compared. The efforts that surround the federal watchlisting regimen can be divided into three broad processes centered on the TSDB: Nomination, which involves the identification of known or suspected terrorists via intelligence collection or law enforcement investigations. The U.S. government has a formal watchlist nomination process. Verification of identities for the TSDB and export of data to screening systems, which involves the creation and maintenance of the TSDB, as well as the compiling and export of special TSDB subsets for various intelligence or law enforcement end users (screeners). Screening, which involves end users—screeners—checking individuals or identities they encounter against information from the TSDB that is exported to screening databases.