Coincidence or cause? In 2011, Norwegian Anders Behring Breivik bombed government buildings in Oslo, and then went to a youth camp where he shot and killed 69 people, mostly teens. As a player of first-person shooter games, Breivik stirred debate when he commented that “I see MW2 [Modern Warfare 2] more as a part of my training-simulation than anything else.” Did his violent game playing—and that of the 2012 mass murderer of Newtown, Connecticut’s first-grade children—contribute to the violence, or was it a merely coincidental association? To explore such questions, psychologists experiment.

Andrew Berwick via www.freak.no/Reuters/Landov