As training and preparedness for active shooter situations continue to grow, so does the risk of confusion in the critical moments when first responders arrive at the scene.
In two recent incidents, "good guys with guns" were mistakenly shot and killed by police responding to the crime in progress.
A mall shopper with a legal handgun carry permit was killed in Hoover, Ala., as he was attempting to help respond to a shooting that terrified Thanksgiving night shoppers. The young man who lost his life was mistakenly identified as the assailant for hours until police realized their mistake and announced the actual shooter was at large.
In another tragic mistake, police responding to a night club shooting in the Chicago area shot and killed the nightspot's armed security guard as he was trying to subdue the suspected shooter.
Active shooter drills and hoax calls can also be a source of danger and confusion.