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Have TSA screeners ever actually prevented a terrorist attack?

Citing national-security concerns, the TSA will not point to any specific cases in which a screener stopped a would-be terrorist at a checkpoint. Nonaffiliated security experts, such as Bruce Schneier (who coined the term "security theater") argue that that's because this has never happened. It's true the TSA doesn't make a habit of keeping success stories a secret. In April 2008, the TSA touted the arrest of U.S. Army veteran Kevin Brown at Orlando International Airport as a victory for its behavioral detection program. Brown was arrested after trying to check luggage containing pipe-bomb-making materials. Airline officials insisted passengers were never in danger, since Brown didn't intend to assemble the bomb on the plane. Moreover, he did not have ties to organized terrorism, and it's not apparent what he wanted to do with the hazardous materials after arriving at his destination. Brown fits into the category of troublemakers that Schneier says the TSA does catch: random nut jobs. (Not professional terrorists with thought-out plans.)
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related: TSA's $200M Sham