Sources:
2013 Report by U.S. Department of Education: “School Crime and Safety”
Report page 7, Adobe page 31 @ http://www.bjs.gov/content/pub/pdf/iscs13.pdf
Are School Homicides ‘Becoming the Norm’? By Jesse Walker – June 11, 2014
http://reason.com/blog/2014/06/11/are-school-homicides-becoming-the-norm
Are mass killings on the increase? Criminologist says no.
By Laura Smith-Spark, CNN – April 3, 2012
http://www.cnn.com/2012/04/03/us/us-mass-killings/
polination.blog 