Response to the crime scene is fundamentally different than notifying the public that an active shooter is on the loose.  If anything, reports of more people with firearms made them respond faster to the crime scene.  I can understand that it takes longer than normal to identify a suspect given the circumstances, but don't go out and tell the public that your police department didn't make a reverse 911 call b/c you relied on Twitter and the news media to get the word out - that's a pretty lame excuse for compromising the public's safety for 5 hrs last night.