First Responder's Toolbox: Planning and Preparedness Can Promote an Effective Response to a Terrorist Attack at Open-Access Events [open pdf - 1MB]
"This product is intended to assist public safety personnel, security personnel, and other event stakeholders in understanding and implementing protective measures to protect crowds at open-access events, especially those that may have limited security support. This information is a starting point to encourage stakeholders to collaborate and seek further advice, resources, and authorities. This product is meant to be scalable to accommodate a variety of locations and venue sizes."
Office of the Director of National Intelligence: https://www.dni.gov/