Liberal/progressives don't like guns. Now, they like gated communities and armed security to protect themselves, but, inherently they don't like guns. With that, the MSM feels the same way.
As with the Zimmerman case in Florida, a simple manipulation of the facts, editing of the 911 call and George Zimmerman is made out to be a racist stalker looking for a reason to shoot some young innocent black.
With this instance, don't wait for the facts, but, create the story that supports your position on guns. What gets the most press, handguns, or assault weapon. Hmmmm, lets go with assault weapon.