This question cannot be answered here with any certainty. In a situation in which you are the only defender, it's certainly possible, perhaps even likely, that any person (other than the AS) whose life would be at risk by such a taken shot would be at even a greater risk if the shot were withheld. Only the actual elements of the event, and the defender's very-hurried analysis of those events, are going to play a factor in determining the response. The defender's skill in making that analysis, and in the shot itself, combined with other variables too numerous to predict here (such as sudden movements on the part of the AS, the person(s) whose life the defender might be risking, and others in the immediate proximity) will play a major part in the final outcome of the shot (or shots.)
With other defenders already engaging, it's likely the other "innocents" are not in much risk from the AS if he's focusing on who is shooting back at him, but they could be from you. I won't risk an innocent if the risk from me would be greater than that from the original threat.