Assuming that one or more rioters *did* fire it matters not whether they *hit* a soldier.
Any dead students found with a gun in their hand????
Again,assuming that one or more shots were fired by rioters,the worst you can say about that is the Guardsmen hit the wrong people...perhaps because of confusion ("the fog of war") or because of poor aim.
All other facts aside, it was my opinion then and now that the Guardsmen were poorly trained and led. Riots had been going on for the previous few years and from what I saw there was a command failure.