Douglas Fox unearths a little-known 1999 Secret Service study of assassinations and assassination attempts over the last 60 years. Forensic psychologist Robert Fein "was able to distill [attackers patterns of thinking] into a handful of recurring motives for killing a public person":
Some hoped to achieve notoriety by killing a well-known person. Others wanted to end their pain by being killed by Secret Service. Still others hoped to avenge a perceived, idiosyncratic grievance unrelated to mainstream politics. Some hoped, unrealistically, to save the country or call attention to a cause. And some hoped to achieve a special relationship with the person they were killing.
Beyond these findings, the study overturns the image of the political or celebrity killer as a menacing stalker. It’s true that politicians and celebrities receive hundreds of threats each year but those threats come from people other than the itchy-fingered trigger-pullers.