Mass shootings in the US, 1982 - 2016 (June 12)
Data from 1982 to 2012 include mass shootings with four or more fatalities. Following a change in the baseline in 2013 by the authorities, data from 2013 onward include mass shootings with three or more fatalities. Shootings stemming from more conventional crimes such as armed robbery or gang violence are excluded.
Source: Mother Jones