hile breivik had a presence in all these cases, some more strongly than others, he was almost never the only influence. In most cases, these would-be terrorists venerated a number of other violent figures, including the Oklahoma City bomber Timothy McVeigh. But a notable theme emerges among their objects of adulation—more men with manifestos.

There is a potency in the combination of words and action, and lone-actor terrorists who write seek to lead their readers through the same process of self-education that led them to act (a phenomenon especially visible in Breivik’s heavily footnoted tract). McVeigh, although he did not leave a manifesto, pointed the world to the revelatory text that shaped him—the racist dystopian novel The Turner Diaries, a book that has inspired at least 200 murders (including 168 killed in the Oklahoma City bombing). Adding to their status, both men left behind tracts that are not only ideological, but instructional. They describe a process of mental awakening alongside practical physical preparations.

These works enjoy a wide reach in the online age, where self-education is a national pastime and internet sleuths race to decode the significance of violent events in real time. The discovery of a Rosetta stone opens the door to forbidden knowledge more swiftly than it can be shut. A gravity well that draws curiosity seekers into the mind of a killer, a manifesto shapes an explanatory narrative for actions that seem inexplicable, imposing meaning on violence that might otherwise be remembered as shapeless chaos.