Here's something that almost all the mass killers of the last fifteen years or so have in common: they've been called "nerds." James Holmes, who allegedly murdered 12 people in a crowded Colorado movie theater on Friday morning, was described as a "nerd" by his uncle within hours of the shooting. Norwegian mass murderer Anders Behring Breivik is, in the Telegraph, a "puffy-faced computer game nerd." Columbine killers Eric Harris and Dylan Klebold were "innocuous nerds," the Los Angeles Times claimed in 1999.

But, uh, were they? Sometime in the last 15 years or so, "nerd" became the catch-all category for mass killers. It's both an identity and an easy explanation: the shooter was quiet and awkward; he must have been bullied; he lashed out. The problem is that it rarely works out that way.

With almost no information about the shooter out on Friday morning, a profiler on MSNBC proposed that Holmes might have been a "dark Trekkie-like person." Over the weekend, ABC News uncovered an "exclusive video" of Holmes giving a short talk at — where else? — science camp. "By most accounts, Holmes lived the life of a normal teen — with a particular interest," the article read, ominously, "in science."

Holmes' science background gets attention only because — weirdly enough for a supposed nerd — he doesn't really seem to be into video games. Breivik was, and his Call of Duty and World of Warcraft fandom got plenty of attention, as did the Doom levels Harris built. Focusing on the perceived nerdiness of the killers helps categorize and demystify them. It explains the anger they're supposed to have felt. It also provides people with a bit of rhetorical revenge: he may have killed dozens, but he's still just a nerd.

But this is inadequate — as explanation, as identification, as stereotyping. Breivik loved video games and sci-fi TV shows — nerdy! — but he also lifted weights, did steroids, and got cosmetic surgery. Harris and Klebold played Doom and built websites — nerds! — but Klebold went to prom with his girlfriend and Harris wrote about bullying "fags" in his journal. If Breivik was a nerd, he wasn't the kind of nerd I'm familiar with; neither were Harris and Klebold; nor was Holmes. And they certainly weren't nerds who would have gotten along with each other.

In this weekend's Times, Dave Cullen — who wrote Columbine, the definitive nonfiction account of Harris and Klebold's massacre — wrote about the kinds of assumptions that tend to follow mass killings: "[W]e all know what happened [at Columbine], right? Two outcast loners exacted revenge against the jocks for relentlessly bullying them." Cullen points out that "Not one bit of that turned out to be true," but who cares? Holmes is already getting painted with the same brush: "Mr. Holmes has already been described as a loner... Nearly every shooter gets tagged with that label, because the public is convinced that that's the profile... [but] the Secret Service report determined that it's usually not true."

Cullen is right to warn against making quick conclusions. ABC reported on Friday that Holmes' mother knew her son was the shooter without reporters needing to tell her — implying that Holmes had been displaying warning signs. Yesterday she categorically disputed ABC's version of events. Sometimes the good and easy story isn't the right one. Not that it necessarily matters. Nerds — self-identified — fear a backlash: "I readied myself for pointed questions which I expected to get from outside the geek community," CNN's Ann Hoevel wrote on Friday evening. "'Why "Batman"?' 'Is the shooter a nerd?' 'Why is it always the loner?'"

Here are some of the things Holmes has been called by people who knew him: a "nerd," as "quiet," "aloof," "reserved," "creepy." Here are some of the other things: "intelligent," "normal," "everyday," "easygoing," "respectful," a "typical American kid." He was into "strategy games" and also football. He joined sex sites and played soccer. One of his neighbors said, in the same breath, that Holmes had "geeky glasses" and also "swagger." Before the narrative locks in it might be worth asking: is James Holmes actually a nerd?