The University of Chicago on Sunday announced that its main campus would be largely closed today, with classes called off, due to a threat of gun violence. The development comes amid worries at many colleges about threats as well as incidents of actual violence. Last week, Western Washington University called off classes on Tuesday due to threats that the university's president has now detailed. And Sunday evening, two film students in Los Angeles set off a panic -- and were arrested -- when they appeared with replicas of weapons on a freeway overpass. During the day on Sunday, a former employee of Ohio State University killed himself in a campus arts center.