Try that stunt most places and see if the results are even close to similar.
Based on the limited info provided, the use of deadly force was never legally appropriate.
I applaud the guy's getting involved and trying to help out, but absolutely condemn the methods he used when he got involved. All the pursesnatcher needs is to find an attorney willing to do up the paperwork for a civil suit - and there are probably lots of such available - and go to town on "Our Hero's" head and wallet. And win!
If you are wearing a gun for anything other than defense of self or innocent others from imminent death or serious bodily injury you need to have sucessfully graduated from the police academy or be wearing the uniform of an armed private security guard.