Malcolm Gladwell, one of the foremost public scholars to disseminate sociological explanations of major social issues of our time, provides an insightful use of emergent norm theory in explaining mass school shootings in recent years.  Students of collective behavior should be particularly interested in his examination of these events.  Read the story here:

http://www.newyorker.com/magazine/2015/10/19/thresholds-of-violence