A man walks into a bank. He shoots the guards, he shoots the tellers, he executes a dozen hostages, and is eventually overpowered and killed by the police. He killed twenty people -- he's a psychopath and a murderer.
Now, rewind the clock. A man walks into a bank, and the guard notices that the man is armed. The guard draws his gun and orders the assailant to drop his weapon. Instead, the assailant shoots a teller. Then another. Then a customer. The guard watches down the barrel of his own weapon and waits, and watches, and waits, occasionally shouting threats and orders, until bodies of women and children litter the floor in blood. Then, the police arrive, overpower the criminal, and kill him. The guard does nothing. Does he sleep at night?
THIRD SCENARIO -- it's not a guard, but another patron, licensed to carry a concealed weapon and trained, competent, and able to operate it.
I DIDNT BRAKE MAH RULE TECHNICALLY