Another criminal with an illegal gun, another gun free zone where he could kill at will. Only way to stop an active shooter is for potential victims to kill him.
Why do democrats want victims disarmed when their laws cannot disarm someone willing to commit suicide.? what sort of punishment would deter a Kamikaze? Nothing, like my late father ( a Deck Gunner in the Pacific Theater) noted, the only way to stop a Kamikaze was to shoot it down before it could hit your ship.
The only way to stop an active shooter is to kill him before he kills other people