QuickTake Q&A: Accounting for the Rise of Lone-Wolf Terrorists

A mass killer, acting alone, strikes in the name of a political cause but without belonging to an organized movement. A disturbed criminal, or a committed terrorist? Security scholars put such murderers in a middle category: the lone-wolf terrorist. The phenomenon isn’t new. But one of the great worries of security officials across the globe is that social media and the active encouragement by groups like Islamic State may be making for a surge in these hard-to-stop killers.

Differing definitions coalesce around these criteria: the perpetrator acts alone and without specific instructions; is politically motivated; and has no formal ties to an organization. So the husband and wife who killed 14 in San Bernardino, California, in 2015, generally aren’t thought to have been lone wolves. Nor is Adam Lanza, who killed 26 people at a school in Newtown, Connecticut, in 2012, and seems to have had only a personal motive. Experts say lone wolves tend to harbor both personal and political grievances. More often than not, they display signs of mental instability. One study found that lone wolves are 13.5 times more likely to have a mental illness than a terrorist acting within a group.