Outside of everyone wearing flak jackets in the DC metropolitan area, anyone who has a video camera should have it fully charged and with them and at the ready when/if they go outside. If there were any witnesses to a shooting w/cameras, they could get immediate initial video of fleeing vehicles from the scene, or whatever. If there was a shooting announced on the radio and somebody in traffic nearby noticed a vehicle speeding away or matching the description and acting odd, they could video as well. This will at least proactively involve the people in the area and give them something to do so they don't worry to death and they can feel they are a part of the solution. We could catch the bastard(s) yet by this kind of cooperation, FBI Most Wanted-show-style.
(Of course, in an area like DC and environs, most common street thugs would be tickled at the prospect of being able to rip off videocameras from vehicles!)