I'd like to say I'd have handled this shooter had i been there, but in reality without being in that situation its impossible to tell how it would have played out. Personally, I believe i would have made the attempt. Maybe it would have affected the outcome, maybe not. I daresay that the proposed situation would be far too chaotic, and the target far too armored to put betting odds on any particular intervention attempt, other than that the distraction created by return fire may have lessened the damage.
-Ex-army and familiar with tear gas and movement under fire.
Oh, normally carry a PX-4 .40 S&W 11+10+10