You’re on your own

Unfortunately the people calling the police in an active shooter event (or an armed robbery, or a home invasion, etc) don?t have three minutes. Lethal violence typically happens in seconds, not minutes. The bad guys do not announce their presence or intentions ten minutes before they start the fireworks. The police are almost always going to be reacting to an act of violence that is ongoing, meaning they are going to be rushing to the scene where people are already bleeding in a valiant effort to limit the carnage. Not to prevent it. To quote from the report: ?Approximately half of the events (49 percent) ended before law enforcement arrived on scene. This points to the phenomenal speed with which these incidents occur.?
The FBI report is acknowledging a simple, inescapable truth: You are on your own.

– Tim at Gun Nuts Media (Emphasis in original.)
Read the whole thing.