No question it was a horrible thing, with 12 innocents losing their lives, and leaving families to morn.
This one was a bit different. The early reporting started in the direction of turning back to the "gun debate", when it was reported that the shooter was armed with an "assault rifle".
It lost steam when it came to light that the killer was armed with a shot gun.
It also came to light that it was a total failure of the "security systems" that missed many signs that should have prevented this guy from entering the Navy Yard legally, with a "secret" security level clearance.
That made it turn to a story about mental illness, going unacknowledged, and a failed system for security checks. Topics the general public likely doesn't feel they can do much about. Therefore the story doesn't have a "rallying call" for action.