I'm not sure about rifles (I think they have to be put in a gun case if its in public) but you can carry handguns either concealed or not.
The right to carry concealed weapons is different depending on the state. Here in lllinois, you can't carry a concealed handgun in public. But if I hopped in a car and drove a few miles over to Saint Louis, on the Missouri side, you CAN carry concealed handguns there. I doubt there's any state that will let you carry long weapons in public.
Related to OP, copycat killers. 'Nuff said. A murder spree happens like that, people will start copying it because people are morons.