Sure enough, a reader has proven me wrong.
I was just directed to this 2005 Associated Press article:
ALBUQUERQUE, N.M. - One man was killed and a woman was injured during an apparent domestic dispute inside a Wal-Mart on the city's southeast side, the second time in less than a week that one of the retail giant's Western stores has been the scene of deadly violence.
Police spokeswoman Trish Hoffman said a witness told authorities that a man had been stabbing the woman inside the store when another man intervened and shot her attacker.
... "It looks like it's a possibility that the guy who shot the other man will be justified," Hoffman said. "From what witnesses are telling us, it corroborates his story that the male was stabbing the female and he intervened."
So there, I stand corrected. Don't shoot.