The only thing that can stop an atrocity like this one is a good person willing and able to use deadly force (whether that's with a gun, a knife, an improvised weapon, or martial arts skills) to stop the killer in their tracks. Because of that, yes, the government and the politicians do have the ability to stop these types of atrocities, but instead they like to encourage these events by making it so fewer good people are able to employ deadly force to stop the bad guy.