Here is the story
I have to ask myself why there was an argument? Unless it was the Citizen yelling for the robber to drop the weapon?
There isn't much info in the article, so I will not speculate on what happened. I bet the video will be on youtube or the news soon enough. I'm glad the Citizen wasn't killed, so if you pray, send a kind word for him to your diety(s) for a speedy recovery. The crook got what he deserved.