A lot of people have made a lot of good points even if I didn't read every post.
It seems to me the question really come down to two things.
1. Are these people who may or may not be a part of the crime visibly moving for a weapon?
2. Are any of these people close enough or closing to engage you with deadly force? Are you sure this person is not coming to your aid or a undercover officer?
If the answer to either of these is no (I am not a lawyer) then it would seem to me to not be a justified shoot for these other people or at the very least, very, very questionable for these people hanging around.
Would it be reasonable to keep your gun drawn and in a ready position but not directly aimed at these other people until you confirm in your mind that you are in imminent danger of death from a clearly defined individual or individuals or determine that you are safe. - I think it would be reasonable if it was for a very brief period immediately after downing a BG with intent, a prosecutor may disagree but it seems reasonable.