Understanding people’s motives may be useful for developing countermessaging, Dr. Cohen said, but it has little value in predicting who will commit future harm. Though many mass shooters have bought into extremist views including radical Islam, misogyny and white supremacy, a vast majority of participants in any given chat room devoted to those beliefs are not plotting mass murder.
(By the same token, a vast majority of people with mental illnesses are not violent, and research suggests that most perpetrators of mass shootings had never been diagnosed with a mental disorder.)
A 2018 F.B.I. report analyzing 63 mass shootings barely mentions the word motive, instead focusing on what experts call pathways to violence. The report describes stress factors and “pre-attack behaviors,” like signaling an intent to harm or displaying an unusual interest in guns. The gunmen in the study exhibited, on average, between four and five such behaviors.
“We have a thing called narrative bias where people like to construct a story that they understand, that’s fairly simple and straightforward and they can apply retrospectively,” said J. Reid Meloy, a forensic psychologist and F.B.I. consultant. “Narrative bias can get in the way of us looking at all the possible motivations or contributions to the risk.”
Decades of data show that most lone actor killers are not motivated by pure ideology, but are nurturing a personal grievance — usually a loss, as of a partner or a job, that is accompanied by anger, humiliation and blame of a particular group, Dr. Meloy said. Of those people with grievances, Dr. Meloy said, only a small subset views violence as a solution, and an even smaller subset has the wherewithal to carry it out.
When presented with the detritus of a killer’s mind, the strands society chooses to extract can tell us less about the perpetrator than they do about ourselves. The fondness of Timothy McVeigh, who bombed a federal building in Oklahoma City in 1995, for “The Turner Diaries,” a book describing a government overthrow and a race war, was initially understood as evidence of his antigovernment views. More recent accounts have used it to underscore his ties to white supremacy.