I thought that was fairly obvious all along. You usually don't hear about a mass shooter at a gun show.Now some tacticians believe the signs themselves may be an invitation to the active killers.
The psychological profile of a mass murderer indicates he is looking to inflict the most casualties as quickly as possible. Also, the data show most active killers have no intention of surviving the event. They may select schools and shopping malls because of the large number of defenseless victims and the virtual guarantee no on the scene one is armed.
As soon as they're confronted by any armed resistance, the shooters typically turn the gun on themselves.
I actually did once read about a moron who walked around a marked cop car to go into a gun store full of staff, customers and at least one LEO and attempt an armed robbery. That was the last thing he ever did.Or a gun store or gun range for that matter. Wonder why?