Were the bombings at the Boston Marathon the work of a sleeper agents or just rogue terrorists? This is just one of the many questions law enforcement will need to sort out during its investigation. However, it’s doubtful the America public will ever hear of these findings, despite rumors that everyone from Al Qaeda to mother Russia has been slowly placing sleeper cells into key cities throughout the United States.

Only months after the September 11 attacks, Newsweek ran an article describing how the FBI and the intelligence agencies were able to thwart a possible sleeper attack against the U.S. Capital. In 2002, an internal report by the FBI indicated 50 to 100 terrorist operatives had infiltrated the U.S. Just two years later the bureau suggested Al-Qaida sleeper cells were operating in 40 states. Earlier this same year Fox News reported possible links between the Al Jazeera network and Muslim sleeper cells in the city of Detroit. Although none of these confirm the existence of either foreign government or terrorist sleeper cells, it does warrant further investigation.

Made up of highly skilled individuals, sleeper agents receive training and instructions long before establishing themselves within their target’s borders. Once in place, the group begins gathering information, establishing logistical support mechanisms and penetrating government agencies in order to carry out acts of espionage, or, as may be the case in Boston, terrorism.

Because sleeper cells work independently, it’s nearly impossible to detect them through electronic monitoring. Generally, it’s the dedicated work of local law enforcement officials and counter intelligence agents, often acting on tips from citizens, to identify these clandestine organizations. What makes sleeper cells such a difficult problem for the U.S. is the groundwork necessary to catch them, often goes against the very nature of our society. For most Americans, the sacrifice of any amount of freedom isn’t something we’re willing to give up.

Whether these men acted alone or utilized a secretive support network is irrelevant regarding America’s need to develop methods to not only locate but also effectively prosecute sleepers before they strike.