would i shoot an intruder in my home? yes. would i shoot someone trying to rob me in my store? yes (if i had a store) would i stop to help someone who was being attacked? yes.
but if push came to shove and i had a gun and people we're running (armed or not, robbing me or not) could i pull the trigger? i cannot see me doing that, no.
and i dont understand why i've had to defend my position on this all day.
I'd say it is far from certain that the suspects were shot in the back as they were running away. This article, for instance, says the suspects and the employees exchanged fire. I would also say that even if someone is running away but still manages to exchange fire, they are far from harmless.
"Investigators say that as the three suspects began to leave, two employees at the business, who were armed with guns, exchanged fire with the teenagers and all three teens were shot."
http://www2.wspa.com/news/2010/may/08/7/teen-killed-apparent-robbery-attempt-ar-154075/