I never said the gun went off "accidentally", you added that word to support your otherwise baseless argument. Guns go off during robberies because the robber got nervous or impatient, because there was a melee, because a third party got involved. By deliberately bringing the gun into the situation, the subsequent claim of an "accidental" firing is nullified.
A guy drinks two quarts of whisky at his favorite bar then drives home. On the way in his drunken state he runs a red light, smashes into a school bus and kills a 9 year old he never met named Mikey. Whoops, sorry Mikey's mom and dad, it was just an accident! Because Tchaffee says so.