Actual Shootings: Did a civilian with a gun stop the criminal?

Does just the average Joe with a concealed gun stop a criminal intent of killing others or does it take more training?  Here are some real cases.  Again, not what the NRA is pushing with everyone should have a gun.

I was trained on the M-16 in the Army and I will say that I would want to continually use the gun to be able to be proficient and NOT DANGEROUS to others in a time of crisis.  Using a gun against another human being is not to be taken lightly - emotions can take over.  A person is not in the same frame mind as they normally are.

Real situations: Did the concealed shooter (untrained) make things better or worse in a crisis?