First, CNN's David Frum:
Next, Buzzfeed's Andrew Kaczynski:
How the NRA handles a mass shooting: Silence http://t.co/vKT2cXqTp5— Andrew Kaczynski (@BuzzFeedAndrew) September 16, 2013
It should be noted Washington D.C. is a gun free zone, as are military bases and the Navy Yard.
UPDATE: The Coalition to Stop Gun Violence has weighed in.