You can see the owner shooting at the BG before he even enters the picture. I'd bet at least one of those shots him him, along with the shots fired as he's much closer. You can see the the owner is standing in a nice position and taking aim. He's not frantic like you usually see in these types of scenarios. 2 shots to the torso, and 1 to the arm and one to the leg, and he runs off as if nothing happened.
My only arm-chair-QB comment (that I'm making from the comfort of my home, in front of my computer, while sipping cocoa) is that if I owned a place like that, in my office, there would be a quick-access long gun available for any time that I had to run onto the store floor and stop a threat. Also, he needs to learn to 'move off the X' when engaging. Regardless, nice job mr. owner!
And thank God the clerk wasn't killed. 