For as long as there has been organized law enforcement in the U.S. there have been “active shooter” scenarios, though that term has only been in vogue for a decade or so now. Historically, active shooting situations are byproducts of other felonies—most often bank robberies. A crime that started out as a robbery, or perhaps a kidnapping, would go bad and turn into a shootout. We used to simply call these events gunfights. The normal situation has involved the bad guys (crooks) shooting it out with the good guys (cops). Law enforcement and society in general have looked at this as something that happens periodically and that is, for lack of a better term, a part of doing business.
On April 20, 1999 in a Colorado town of less than 30,000 people, an event occurred that changed the way law enforcement would view felonious shootings forever. We all know what happened at the Columbine High School. What is most significant is that the accepted thought process for law enforcement at that time was the old standard: a bad-guys-versus-good-guys gunfight. The rules had changed, but we didn’t yet know it.