To save an 82-year-old grandmother huddled alone in her house in Pec, one rare Serb soldier who had not lost his own humanity posted an eloquent sign on her front door: "A person lives here."

But most of his comrades apparently had learned to see Naxhie Salilu as something less than a person. Despite the sign on the door, Serb soldiers set fire to her house -- and when she managed to douse the flames, they tried again, and then a third time, according to an account by Washington Post reporter R. Jeffrey Smith. Only the arrival of NATO troops and the withdrawal of the Serbs saved her life.

Many others were not saved, of course -- how many others we still do not know. Ten thousand, one British official guesses, but the estimate will likely rise. Every village, it seems, has its mass grave, its blood-stained cellars, its scraps of clothing and bones poking above hurriedly shoveled earth.

And so once again the rest of us are left to wonder: How could people do such things? How could Serb soldiers, some of them hardly more than boys, loving sons in many cases, one perhaps an affectionate tease of his kid sister back home, another devoted to a grandmother of his own -- how could they try to burn an 82-year-old grandmother alive, and joke about eating her once she was cooked?

How could they shoot old men, throw grenades into rooms packed with women and children, decapitate and mutilate and torture?

These are not new questions, and there will be no new answers -- on some level, no answer at all. And yet, as after the Holocaust, Cambodia's killing fields and Rwanda's genocide, it will not be enough to say that these atrocities are inexplicable.

They were, it's important first to note, planned and deliberate. Slobodan Milosevic's campaign to force most ethnic Albanians to leave Kosovo was carefully organized, highly complex and astonishingly efficient. It relied on terror -- on "demonstration killings," as Kenneth Roth of Human Rights Watch said last week -- as a motivating force.

And though most deportees are now likely to return, it would not be accurate to say that Milosevic's campaign entirely failed. NATO did well to stand up to Serbian aggression, but that does not mean that, as President Clinton said Friday, "We have reversed it."

Kosovo is laid waste. Everything of value -- from washing machines to medical equipment to children's doll collections to German marks -- has been looted and carted back to territory that Milosevic still controls. The once lively market town of Pec, like other Kosovo towns and cities, is in ruins. Virtually every family has lost a loved one or suffered in some other way. Far from being "reversed," the damage that Serb forces inflicted will reverberate down through generations.

But if Milosevic had a plan, that does not explain how he found so many people willing to carry it out. And yet here, too, there are answers of a sort.

They start, as always, with a dictatorship using a closed and manipulated press to dehumanize its intended victims. Neil Kressel, author of "Mass Hate: The Global Rise of Genocide and Terror," notes that Nazi Germany made movies alternating footage of rats gnawing through granaries with footage of Jews working in Germany businesses. Rwandan Hutus referred to Tutsis as "insects." In Serbia, Kosovo Muslims were dehumanized as backward, overbreeding infidels and demonized as dangerous rapists of Serbian women.

The next step is authorization, the apparent granting of legal and moral approval from someone higher up. Finally, Kressel said, comes routinization.

It's not yet clear how many of the worst atrocities were committed by the army and police, how many by local Serb civilians and how many by paramilitary thugs such as those led by the war criminal Arkan. Such thugs often develop such a strong sense of identification with their groups, psychologists say, that when an order comes to kill or rape, refusing becomes too painful a repudiation of identity. Rebels in Sierra Leone have taken that phenomenon to its extreme, seizing pre-adolescent boys and forcing them to kill their own relatives or villagers so that the criminal band becomes their only possible family.

A principal motive for the paramilitaries in Kosovo, according to Branimir Anzulovic, was plunder.

"You can find such criminals in any society," said Anzulovic, author of "Heavenly Serbia: From Myth to Genocide." "But then there is another question -- the silence of most Serbs, their failure to express any outrage."

There are a few brave and honest Serbs who have spoken out against Milosevic's war against civilians. But all of Serbia's institutions work against such voices. The media are controlled. The Serbian Orthodox Church, even as it called for Milosevic's resignation last week, could summon indignation only about the Serb exodus from Kosovo, not the atrocities committed against the Muslim Kosovars.

For neither side can there be rapid repair. For many Kosovars, euphoric now at going home, there will soon come "a period of real recognition of the extent of their loss and the difficulty of recovery," said Dr. Jennifer Leaning, who has worked with Kosovars in association with Physicians for Human Rights.

In the long run, though, it may take Serbian society even longer to heal, since even the first step -- acknowledgment of its crimes -- seems so distant.

"We can all start working like nothing happened," a municipal Serb police chief in Kosovo, Tomislav Simic, said last week. Of all the imaginable outcomes to this tragedy, that is probably the only one that can be ruled out with certainty.

The writer is a member of the editorial page staff.