Terrorists frequently engage in surveillance activities when selecting a target and planning an attack. Needless to say, when we are able to spot such surveillance activities, we stand a greater chance of preventing an attack. In 2007, for example, authorities thwarted a terrorist plot in Germany when they caught people surveying U.S. military facilities near Hanau. In 2006, two men were charged with videotaping the U.S. Capitol building, the World Bank, a Masonic temple and a fuel depot in Washington, D.C., to send to overseas terrorist groups. And in 2004, the U.S. Department of Homeland Security raised the terrorist threat level following reports of terrorist surveillance of key financial institutions in New York City, New Jersey and Washington, D.C.
Using 911 calls to detect terrorism threats
Strom, K., Hollywood, J., & Pope, M. (2009). Using 911 calls to detect terrorism threats. NIJ Journal, 263.