On the last day of classes this year at Crosby High School in economically hard-bitten Waterbury, Conn., a fight broke out that spilled onto the street. Police responded with pepper spray, and six students were arrested. Tragedy was averted—for now. Who knows if those resentments will fester over the summer and return with renewed vigor (and guns) in the fall? Who knows anymore at any American high school?

During the last week of classes at Columbine High School in an affluent suburb of Denver, two students acted out their own anger with guns, at the cost of 12 lives. That "massacre," which took place on April 20, 1999, is the subject of Dave Cullen's harrowing new book Columbine. Just that word, "Columbine," appears on the cover, above a photograph of the school. No other words are needed.

The day began and ended very much as it had for the 18 Islamic terrorists on Sept. 11, 2001: the desired carnage inflicted, the perpetrators dead, the rest of the world to sit back and wonder "Why?" The difference, and what makes Columbine particularly chilling, is that the perps, Eric Harris and Dylan Klebold, were our own homegrown terrorists, and their goals were even less clear than bin Laden's.

Barely out of their boyhoods, one wore a black T-shirt with "Wrath" emblazoned across its front and a Red Sox cap turned backwards, while the other sported a T-shirt that read "Natural Selection." They both wore black combat boots. They were, apparently, going to war, but against what? Boredom? And against whom?

Each of these killers inexplicably had (illegally obtained) semi-automatics and shotguns, as well as backpacks filled with pipe bombs. It's a miracle of sorts that the carnage wasn't worse, because their original plan was to blow up the school with propane bombs and then pick people off as they ran outside in a panic. Bombs were planted throughout the building, some in such a way as to snap concrete pillars and crush victims to death at the peak of lunch period. Harris and Klebold were not without ambition: they aimed to top Tim McVeigh's death count in Oklahoma City.

But the bombs didn't blow. So the two killers stormed the school, laughing as they blew people away, as if playing a violent video game. Some of the other students even laughed at this pair when they first opened fire, thinking it was a prank. Oh, Eric and Dylan were such pranksters!

Arguably even more frightening than the 40 pages of Cullen's minute-by-minute account of the massacre are the 300 pages of reaction that follow it—the lives ruined, the attempts to find meaning, the fundamentalists whipping up a fury, some even couching it as part of biblical revelation, sending the twisted message to 2,000 high-schoolers already traumatized beyond any adult's conception, the ignorant zealots heaping more trauma on them after the fact. How does one find meaning in an essentially meaningless act?

Complicit as always, Cullen says, was the media, for fomenting instant myths about the killers. It seemed so simple: Goth losers were shooting jock winners. Outcasts shooting the future cream of the crop. Except it wasn't true. Both Eric and Dylan were as fully engaged in high school life—and well liked by a circle of friends—as anyone at Columbine. Though all of these themes were floated as motives for the killers, and then quickly proven false, Cullen writes, "the public still takes them for granted. Why?"

Because it's easier and less threatening than having a civil conversation about the easy access to guns in this country. Until that discussion occurs, and appropriate actions taken, expect more of the same. And consider it a miracle if it doesn't recur.