I recently took a basic handgun class that was taught by active duty and retired police officers. There instructions in a self defense situation were: "if someone is worth shooting one time they are worth shooting 5 times". Very few normal handgun calibers have the ability to completely incompacitate someone who is intent on doing you harm or killing you. Unless you make a head shot or hit them center mass which does not guarentee that they will drop or retreat. Therefor it may take multiple shots to slow the attacker down or kill them if needed. This makes it that much more important to make sure you are justified before making the decision to shoot someone.

As far as the ferguson case goes, I think a broken eye socket and he still coming forward is justifiable for multiple shots. I am not up on all the details of the case but what I have read I think it was justifiable. My $0.02.

And it helps for the only story of the events to be YOUR story of what transpired.