In the words of Thomas Sowell:
Full article: The Bullet Counters by Thomas Sowell on Creators.com - A Syndicate Of Talent
Its not the same situation, he eliminated the threat, went and got an entirely different gun and pumped 5 rounds in him while they were laying on the ground. This isnt the same as someone pointing a gun at you and you unload a clip on them.
I am a gun lover and always the first person to defend someone in this store owners position but I think he went beyond self defense, I couldnt believe it when he walked in back and grabbed another gun and unloaded it.