On Tuesday night, George Sodini executed a terrible plan. He opened fire at an aerobics class in Bridgeville, Pennsylvania, and shot 12 women, 3 fatally, before turning the gun on himself. This was not a spontaneous attack: he had mapped out his plan in painstaking detail in notes kept in an online diary. Those notes now provide a stark look at the mind of a killer. Dr. Michael Welner, a forensic psychiatrist and adjunct law professor at Duquesne University in Pittsburgh, who studies killers, joins us with a look at the psychological profile of a mass murderer.