Police and Federal Agents need to be careful they are not allowing the sniper and those behind him to set them up for a major terrorist incident.
I envision a sniper attack causing authorities to close the highway system around DC then the main elements of the Terrorist cell detonating a Chemical, biological or dirty nuke, possibly by remote. My guess is a biologic like smallpox because of the difficulty of detecting it.
I think we are playing right into their hands by locking down a major corridor like that and need to be alert to the possibility of a larger plan. We are getting people out into the open and concentrating them at a location of their choosing.