Simran, Though I dont agree with bunty below comparing Sikh carnage with this ridiculous and horrible act of this south korean, we need to keep in mind the professional way how law is enforced by US. Policemen cannot do much if govt allows guns and ammunition to be made available legally in such an easy manner. As you have rightly mentioned, the gun control lobby in USA is so strong, and the only way to control this menace is by bringing in stringent law that makes the access / purchase of weapons and ammunition difficult for citizens.
