Why?Because they didn't have at the moment.

Have you ever thought about this: before the firing, for how long the polices and army tried to stop the 'mobs' with their bare hands? What I saw from the TV was: the polices and soldiers built human wall to stop the crowd, not even used any 'civilized' weapon like those in civilized governments do. Have you seen any civilized government doing these? Show me some pics that the polices of the civilized governments facing the similar situation with their bare hands, no guns, no bats, no sheilds, no horses, no water canons... Show me!!