Last year James Fitch, chief of campus police at North Central Texas College, patrolled several buildings during an emergency-alert test to see how faculty and students responded. Later that day his office noticed that a student had posted a warning on Facebook: A man was meandering through a campus hallway, the student reported, with a loaded gun.
http://chronicle.com/article/To-Track-a-Predator-How-the/236734 Chronicle of Higher Education