"Across the United States, Americans congregate in faith-based venues to worship, learn, play, and bond as a community. However, public gatherings are vulnerable, and adversaries may perceive houses of worship as attractive targets where they can inflict mass casualties, cause substantial psychological impacts, and draw extensive media coverage. The Department of Homeland Security (DHS) offers numerous resources to assist faith-based and community organizations with their efforts to prepare for all types of hazards, whether natural or man-made." This factsheet provides information on how to prepare for and respond to an active shooter, how to protect businesses, what to do until help arrives, and how to prevent arson in houses of worship.
Federal Emergency Management Agency (FEMA): http://www.fema.gov/