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 Terrorist Screening Center, the Hub of Watchlisting

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 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.