Watch the CBS Reports documentary "The Watchlist: 20 Years of Tracking Suspected Terrorists" in the video player above.

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The U.S. government's terrorist watchlist has nearly doubled in size in just six years, a recent investigation has revealed. 

An extensive analysis of various sources, including court records, government documents, and interviews with numerous intelligence community leaders, has shown that the consolidated database of individuals has not only been quietly expanding in number but also in its scope of targets.

The figures speak for themselves. When it was initially launched on Dec. 1, 2003, the consolidated watchlist — now referred to as the Terrorist Screening Dataset — contained approximately 120,000 individuals. By 2017, the most recent publicly confirmed numbers, it had grown nearly tenfold to include 1,160,000 individuals. Now, at the end of 2023, the Terrorist Screening Dataset encompasses the names of around 2 million people that the government considers known or suspected terrorists, including thousands of Americans, according to the investigation.

"It doesn't necessarily mean they are terrorists," cautioned Russ Travers, a veteran of the U.S. intelligence community for four decades who played a role in creating the watchlist. "It simply means that there is something that has prompted a department or agency to believe, 'This person requires closer scrutiny.'"

Consequences of Being on a Watchlist

Being on a watchlist can have significant consequences on people's lives. In countless civil lawsuits over the past 20 years, people have described how they believe the watchlist caused them to be stopped from flying home after a vacation, to fail a background check to get jobs, or to have their phones and computers searched. Others said it triggered law enforcement to handcuff them at gunpoint, or that they were detained and interrogated by foreign intelligence services.

The TSA redress department director stated in late 2006 that over the preceding year alone, the names of approximately 30,000 airline passengers were mistakenly matched with those appearing on federal watchlists.

Someone who believes they've been wrongfully impacted by the watchlist can file a complaint with the Department of Homeland Security requesting redress. However, this is unlikely to help those who are on the watchlist, whether they're innocent or not. In one case, it took a Stanford PhD student fighting a nine-year court battle to prove that she was wrongfully listed; the FBI finally admitted she was watchlisted by mistake because an agent had accidentally checked a wrong box.

The FBI recently updated its criteria for adding individuals to the watchlist, requiring more identifying information. If sufficient information is not provided, individuals won't be listed, and those already on the list may be removed if their files are deemed too thin under the new standard. The collection of biometrics, particularly faces and fingerprints, is also being prioritized to reduce cases of mistaken identity, according to officials.

U.S. national security assessments for 2023 and 2024 indicate that both foreign and domestic terrorism threats are increasing. The government views the watchlist as an essential component of its "early warning system," according to intelligence community insiders.

However, civil liberties advocates and former counterterrorism insiders have expressed concerns about the expansion of the watchlist. They highlight government abuses, errors, and a lack of accountability over the past two decades since its inception.

"People might think that the watchlisting system is a remnant of 9/11. It is not," said Hina Shamsi, National Security Project director at the American Civil Liberties Union. "This is a system that has only expanded."

A number of federal lawsuits allege that FBI agents have violated policy by adding innocent people to the database to coerce them into becoming informants. Critics argue that efforts at accountability have been hindered by a culture of secrecy and a lack of transparency, issues that the Biden administration acknowledges.