In this instance banning guns probably wouldn't have done any good anyway since it is looking more and more likely it was a terrorist attack as IS have claimed responsibility .
Unless all the guns sold in America are going to be reclaimed by the authorities and destroyed then banning guns is pointless for the purposes of restricting the availability .We have fire arms bans in place in this country and it is ridiculously easy to get a gun
especially when we have characters like this turning blank pistols into deadly fire arms