What could make 11- and 13-year-old boys meticulously plot an ambush and then lie in waiting outside an Arkansas school to mow down classmates and teachers?
Or make a 14-year-old shoot to death three and wound five others at a Kentucky school three months ago?
Or make a 16-year-old kill two and wound seven at a Mississippi school five months ago?
Officials say the number of incidents of school violence has not grown significantly over the last two decades.
But that's of little comfort to a nation grappling with three such deadly incidents that defy easy explanation, and grappling with youth violence in general even as adult crime rates dramatically decline.
There are no pat explanations. But there does seem to be at least one common denominator: young people who felt aggrieved or left out for one reason or another.
As police searched for a motive in the Arkansas shootings, one early report pointed to the fact that the older boy was upset after breaking up with his girlfriend. Schoolmates said he had vowed to shoot all of the girls who had ever broken up with him.
That sounds suspiciously like the search for "respect" -- and vengeance when it's not given -- that motivates many urban kids who get caught up in deadly violence. And it proves how vulnerable all kids -- urban, suburban or rural -- are as they grapple today with questions of identity and belonging.
In the other incidents -- in which one young killer felt bullied and the other reportedly had fallen into a cult -- similar questions of what these kids were searching for hung in the air after the gunpowder had settled.
Of course, teens and preteens have always felt alienated. It is almost a rite of transition.
What is different is that they didn't always live in a culture saturated with so many guns or with messages everywhere that guns are a way to attack any problem -- including the problem of not being accepted.
The gun lobby will protest that people will always find a way to kill and that guns shouldn't be blamed. But does anyone believe so many people would have died or been wounded in this incident if the boys had been forced to rely on knives, fists or baseball bats?
The impersonal nature of being able to kill from a distance -- coldly, almost antiseptically -- makes killing easier for kids whose psychological faculties haven't developed enough to let some of them even appreciate the full magnitude of what they're doing.
Maybe that's why doctors have urged Americans to begin thinking of gun violence as a public-health epidemic and note that more teens die from it than from all natural causes combined.
Such realities give this society two obvious choices. It can better regulate access to guns -- locking them up, for instance -- that can be used to act on teen-age angst. And it can search for ways to reduce that angst with programs that reach out to kids trying to cope in a society that is much more atomized and that sends them more inappropriate messages than the society their elders faced.
Though neither can save all teens from their own demons, both approaches make sense. And both typically get little attention -- until something like this happens.