Well let me just start by saying that if we find out there were more than 11 shots fired (from shell casings) then this won't be correct, but the reason I'm assuming the shot to the arm came from behind is because without that being true, the math doesn't add up. So let's start with a big IF.
IF there are only 11 shots, then group B had to be the six shots fired. Group C only has 4 shots fired, so that cannot possibly account for all six hits. IF the autopsy is correct, and 5 shots are from the front with 1 shot being possible as being from behind, then logic says the shot by the car had to have hit.
Picture a math logic puzzle:
So that's why I think it went down the way I've been saying. Now, if there were more shots fired, again, this all changes. But since most people agree that the police issue gun would hold what, 12 shots max? Then where would there be time to reload in all this?