Over the last few decades, spree killings and mass murders have been on the rise. So-called "rage killers" are different from serial murderers, their anger building until they turn it loose on society, killing as many people as they can in a very short period of time. What links these acts of evil? From Charles Whitman, the Texas clock tower sniper, to Charles Starkweather, the real "Natural Born Killer," science reveals new clues into the psychology behind these seemingly senseless crimes.