"Terrorist precursor crimes, offenses committed to facilitate a particular attack or promote a terrorist campaign's objectives, are thought to be often carried out far away from the primary theater of conflict associated with a terrorist group. Much of the precursor activity, especially with regard to crimes conducted for the purpose of fundraising, takes place in wealthy Western countries, including the United States. Precursor crimes, known and/or alleged, include various fraud schemes, petty crime, identity and immigration crimes, the counterfeit of goods, narcotics trade, and illegal weapons procurement, amongst others. The implications of domestically occurring terrorist precursor crimes on the current threat environment, and specifically the United State's security posture, are not fully understood. It does appear, however, that the likely presence of terrorist groups or their sympathizers conducting precursor crimes within the United States presents a series of unique problems and challenges for U.S. law enforcement and intelligence communities' counterterrorism programs, many of which have important implications for Congress. As Congress conducts oversight of the federal agencies engaged in terrorist precursor crime investigations and intelligence efforts, this phenomenon and U.S. efforts to identify, investigate, and counter it may be of particular concern."
CRS Report for Congress, RL34014