These studies were modeled after earlier research into whether gory television shows could be linked to increases in violent crime. At first, those studies were equivocal, according to Ferguson. But that changed by the 1970s. Perhaps because the actual murder rate was rising, scholarship on the subject started shifting from inconclusive to absolutely certain that television caused violence—even if only by means of a correlation with aggression.

As subjects of study, video games complicate matters. They aren’t captured on film, like television, so the definition of “violence” in a game has always remained abstract: Is eating a Pac-Man monster violent? What about firing a dot at an insect abdomen in Centipede? Ferguson says the results of early video-game studies were all over the place. Some found effects; others didn’t. But, he told me, “people were honest”: Researchers acknowledged the limitations of the studies and the inconclusiveness of their results.

By the 1990s, the tide had turned. Computer graphics, though still relatively simple, were becoming more realistic. The industry also began targeting the now-older kids (and young adults) who had made up the Atari and Nintendo generations of the prior decade. Soon enough, concerns about violent video games also reached Washington. In 1993 and 1994, Senators Joe Lieberman and Herb Kohl—both Democrats—convened hearings about violent games and their possible effects on children. The interest had been sparked largely by Mortal Kombat, a fighting game with realistic and gruesome details, including spurting blood and decapitation. In the aftermath of the hearings, Lieberman introduced legislation to create a rating commission for games; instead, an independent group, the Entertainment Software Rating Board, was established, the games equivalent of the Motion Picture Association of America.

Then, in 1999, Dylan Klebold and Eric Harris killed 13 people and injured 20 more at Columbine High School in Colorado. During the investigation, it became clear that the two had played and enjoyed Doom, the 1993 game that essentially invented the first-person-shooter genre. Klebold and Harris seemed to have used it as a tactical tool, creating maps to plan their attack. The unique shock of the attack might have accelerated interest from behavioral scientists, Ferguson speculated. “After Columbine,” he said, “the honesty stopped.”

Games also became rapidly more mature in their themes and audiences. Grand Theft Auto added misogyny and criminality atop the violence. Doom’s progeny, such as Counter-Strike and Call of Duty, added human enemies and military themes. Video games had incited moral panics for decades by this time—from concerns about driving over stick figures in 1976’s Death Race to the lurid draw of the video arcade in 1982 to the gore in Mortal Kombat in 1993. Inside the community that played them, the changes seemed evolutionary—and the players had grown older, besides. But from the outside, among those who didn’t understand video games, the early 2000s represented a definitive shift toward moral depravity.