The horrific mass murder at a movie theater in Colorado on July 20 and another at a Sikh temple in Wisconsin on August 5 are the latest in an epidemic of such gun violence over the last three decades. Since 1982, there have been at least 58 mass murders* carried out with firearms across the country, with the killings unfolding in 30 states from Massachusetts to Hawaii. We've mapped them below, including details on the shooters' identities, the types of weapons they used, and the number of victims they injured and killed. Of the 134 guns possessed by the killers,...