Perpetrators
Angry young Men and Mass Killings
http://www.huffingtonpost.com/john-roman-phd/angry-young-men-and-mass_b_10503106.html
By continent and region
Why the U.S. Has 31% of the World's Mass Shootings
http://time.com/4007909/gun-violence-mass-shootings/
Mass shooting
ResearchGate - Temporarily Unavailable
https://www.researchgate.net/publication/270480045_Mass_Shootings_in_America_Moving_Beyond_Newtown