Amor Masovic has the gaze and mournful air of a man who never gets enough sleep. For nearly two decades, his job has been to find the mass graves containing thousands who disappeared during the Bosnian war. He is very good at what he does, and he has a mind for numbers. When I first met him in the summer of 2012, Masovic calculated that he and his colleagues at the Bosnian government’s Missing Persons Institute had found more than 700 mass graves, containing the remains of nearly 25,000 people.

“I think we’ve found all the larger ones now,” Masovic told me as we sat in a smoke-filled cafe in Sarajevo. He had just returned from another foray into the field; his boots were still caked in mud. “But that still leaves a lot of smaller ones.” Exactly how many more depends on the definition of “mass grave.” If you go by the current definition (a grave that contains three or more people), then Masovic’s guess is that there are 80 to 100 still to be discovered. Of those, he suspects that 15 to 20 contain more than 50 bodies.

He has any number of methods for locating the graves. He goes by the testimonies of survivors or by cajoling people in Bosnia’s small villages and towns into pointing him toward places they know about. Other times it’s simply a matter of reading subtle changes in the landscape. “I’ve been doing this for so long,” he said, “that I can be walking or driving somewhere, and I see a spot and think, Hmm, that would be a good place for a grave. I’ve found some that way.” In fact, “grave” is often a misnomer. Masovic has found human remains in mineshafts and caves and dry lakebeds. “They’re everywhere,” he said. “Everywhere you can think of.”

Of all the atrocities committed throughout Bosnia between 1992 and 1995, the one that compels Masovic the most is Srebrenica. In some respects, this is hardly surprising: Srebrenica has come to symbolize the Bosnian war’s unspeakable brutality and the international community’s colossal failure when confronting it. Located in a tiny valley in eastern Bosnia and Herzegovina, it was the site of one of the war’s most desperate contests, a marooned enclave in which a couple of thousand government soldiers, along with as many as 40,000 mostly Muslim refugees, held out for three years against a siege by Serb separatist fighters.

For more than half that time, Srebrenica was under international military protection, one of six United Nations-designated “safe areas” established throughout the country in 1993. That status proved meaningless when the Serbs launched an all-out assault in July 1995. Instead of resisting, the U.N. Protection Force in Srebrenica stood down, and over the next few days, the Serbs hunted and killed more than 8,000 men and boys, most of whom were trying to escape the enclave by foot. It was the worst slaughter, and the first officially recognized act of genocide, to occur on European soil since World War II.

For Masovic, the massacre in Srebrenica presents a special professional challenge. Only about a thousand of those fleeing were killed outright. The other 7,000 were captured and taken to various killing fields for execution, their bodies dumped into mass graves. Shortly afterward, however, Serb commanders ordered the original graves dug up and the remains moved to a series of smaller mass graves along the Drina River basin — the so-called Valley of Death — that they hoped would never be found. “This has made Srebrenica our greatest challenge,” Masovic said.

But there is something else, too. The slaughter occurred in the waning days of the war, when the signs were that the international community was about to force a political settlement in Bosnia. Consequently the killings were particularly senseless, one last orgy of bloodletting before the fighting stopped.

“You could say that maybe I am even haunted by that,” Masovic said, staring at the cafe table and absently kneading his fingers. “The evidence gives the chance for moral satisfaction,” he said. “To try to give it some kind of meaning, to at least help the families, this is why it’s so important to me to find those men.”

Masovic began to muse on the potential whereabouts of the 1,100 or so men still unaccounted for. “Probably it means there are some graves we haven’t found,” he muttered, “or maybe a lot of them were thrown in the Drina.” Periodically he hikes portions of the trail that the doomed men tried to take out of the valley. In the early years, he almost always came upon remains, but that has now become rare. “At this point, I don’t think there’s many more still in the forest,” he said. “Maybe 50, 100.”

Masovic is one of the point men in an extraordinary international effort to identify the victims and the perpetrators of the Bosnian war. In 2012, after years of meticulous labor, the Norwegian-funded Research and Documentation Center in Sarajevo released “The Bosnian Book of the Dead,” a four-volume compendium that sought to list every known fatality of the conflict (a tally that came in at slightly more than 100,000 rather than the 200,000 figure often cited by the media). That report also underscored the highly sectarian nature of the conflict; of the 43,000 civilians killed, 82 percent were Muslims, and 10 percent were Serbs.

This accounting has been especially comprehensive with Srebrenica. Since 1999, Masovic and his colleagues have transferred any remains discovered there to a mortuary in Tuzla that was built by the International Commission on Missing Persons (I.C.M.P.). Working off a DNA database of more than 22,000 living relatives of the missing, the I.C.M.P. has positively identified nearly 7,000 of those killed — and Masovic’s organization has come up with a remarkably specific number for the dead: 8,372. At the same time, international war-crime prosecutors have intently focused on the massacre, indicting 21 people on charges that include everything from “inhumane acts” to genocide. All of these efforts taken together make Srebrenica one of the most thoroughly documented war crimes in history.

Amid Masovic’s grim recitation, though, there was something I found puzzling. Mass murder on the scale that occurred in Srebrenica must have required hundreds of actors — to stand guard over the captives, to transport them to the killing fields, to bury and then rebury them. At least some of these participants must have confided to a wife, a brother, a priest. Given this enormous pool of potential informants, how could there be many secrets left, many more graves to be found? I asked Masovic what percentage of his discoveries had been a result of conscience-stricken Serbs’ coming forward.

“Percentage?” He smiled thinly. Other than a posthumous letter, he has received only one other tip, a note signed simply, “A Serb from Foca,” that led him to a mass grave. “Maybe you can say this man was stricken by half-conscience,” Masovic said, “because he still didn’t have the courage to sign his name. But other than that Serb? Not one. In 17 years, not one.”

That detail goes to the heart of the struggle facing Bosnia nearly two decades after the war: How do you knit back together a society when those primarily responsible for tearing it apart don’t believe they did anything wrong?

As battlefields go, the topography of Srebrenica is unusually simple: a pretty Alpine valley, seven miles long and perhaps a half-mile wide, with a fast-flowing stream running through it. The hillsides are green pastures dotted by whitewashed farmhouses that gradually give over, in the higher reaches, to thick evergreen forest. At the southern end of the valley is the small town of Srebrenica. At the other end, where the land opens up and the stream joins the much broader Drina River basin, is Bratunac. Roughly halfway between these two settlements is the village of Potocari, where the United Nations military compound was located during the war.

Directly across the road from the former compound is a cemetery reserved for those massacred in the summer of 1995, more than 6,000 graves climbing the hillside in an undulating expanse of identical white stone steles — the traditional Bosnian Muslim headstone — a single one marked with a Christian cross. Next to the Potocari cemetery’s gates stands a small gift shop that sells shawls and jewelry made by the female relatives of the dead. It is operated by a 64-year-old Muslim woman named Fazila Efendic, whose husband and only son are interred on the hill above her shop.

Within the Balkan mélange of competing religious and ethnic groups (the so-called powder keg of Europe), Bosnia and Herzegovina was regarded as an especially volatile place, a country with significant populations of Muslims, Catholic Croats and Orthodox Serbs. Over the centuries, religious tensions periodically led to paroxysms of violence, but the rivalries appeared to be finally put to rest when the strongman Josip Broz Tito consolidated the federation of Yugoslavia after World War II.

Fazila Efendic recalls that time in almost nostalgic terms. I spent an afternoon with her in the living room of her pleasant, modern home in Potocari — her old one was destroyed in the war — a quarter mile or so from the cemetery. “During the Tito time,” Efendic said, “we got along perfectly with the Serbs. There was no separation, no difference, we really didn’t think about these things at all.”

Rather than disappearing, however, it seems the ethnic hatreds went underground during the Tito era, and they came raging back when Bosnia declared its independence from the disintegrating Yugoslav federation in April 1992. Within days, separatist militias made up of Bosnia’s Serb and Croat minorities rejected the central government in Sarajevo and, with major military and financial support from the republics of Serbia and Croatia, seized huge swaths of Bosnia to establish their own minirepublics.

The Serb leadership had a radical solution to the old Balkan riddle of competing heritages: They would solidify their claim to what they now called Srpska through ethnic cleansing. Within weeks, thousands of Muslim civilians had been murdered, with tens of thousands more forced from their ancestral homes through an organized campaign of terror, mass burnings and rape.

Nowhere was this ethnic cleansing more systematic or brutal than in the Bratunac-Srebrenica area. In the first few days of the war, Bosnian government forces took control of the Srebrenica valley, but they were soon trapped there by Srpska militiamen, aided by soldiers from neighboring Serbia.

Very quickly, the Bratunac region was purged of most of its Muslim residents. Mosques were ringed with dynamite and blown to pieces, their ruins then ground to dust by bulldozers. Vacated Muslim farms and hamlets were destroyed. In many places along the Drina, the eradication effort extended to Muslim historical sites and cemeteries.

At her home in Potocari, Fazila Efendic heard horror stories of torture and mass executions from the refugees who began flooding into the Srebrenica valley. “At first, I didn’t completely believe them,” she told me, “because it was like hearing of things from the Dark Ages.”

Three miles down the road from Efendic’s home, in Bratunac, I met a 48-year-old Serbian woman named Radojka Filipovic, who told a very different story. We sat in the unheated office of a group called the Association of Families of Captured and Fallen Soldiers and Civilians of Republika Srpska, and as Filipovic talked, there was the disorienting sense of having entered a universe in which all historical facts were reversed. Here, it was the Muslims who were the aggressors, the Serbs the victims. Filipovic wanted to discuss the “atrocities” committed by the Bosnian government forces in Srebrenica. Effectively cut off from the rest of government-held territory, and saddled with the task of protecting tens of thousands of refugees who fled into the village, the government fighters periodically launched raiding parties across the Serb siege lines in search of food. During these raids, they occasionally killed Serb civilians and Filipovic appeared to have memorized the date and precise circumstances of each of these deaths.

“We know that on Aug. 8, 1992,” she claimed, “the Muslims killed a man by cutting off his head. Then they took his head back to Srebrenica and used it as a soccer ball. This has all been thoroughly verified.”

Understandably, the centerpiece of Filipovic’s narrative was the death of her husband, Dragan, and her father-in-law in Bjelovac, a village a few miles from Bratunac, on Dec. 14, 1992. “The Muslims surrounded it the night before,” she said, “and then they came in at dawn to kill everyone they could find. They butchered 68 people in Bjelovac that day.” (According to the Research and Documentation Center, a majority of those killed in the Bjelovac area on Dec. 14, 1992, were combatants. Of the 17 confirmed civilian fatalities, five were victims of bombs dropped from a Serbian government warplane. Further, the center can confirm only 154 Serb civilian deaths in the Bratunac region over the course of the war, many of them victims of collateral damage.)

“You will not find one Muslim who will admit to these things,” Filipovic continued. “If we are ever to have peace here, we must stop trying to place blame on one side or the other and recognize that both sides suffered, both did bad things.”

At least initially, this spirit of moral equivalence was shared by many of the outside powers that might have helped bring the carnage to an end. Well into 1993, the ongoing Bosnian tragedy provoked intense hand-wringing in Washington and Western European capitals. When finally the sheer scale of Serbian atrocities compelled the international community to act, it was with an ever-changing grab bag of half-measures, all of them overseen by a political and military chain of command so complex as to induce paralysis.

Though that might have been the point. Just as the reluctance to affix blame meant there was no moral imperative to forcefully respond, so the unworkable apparatus set up once the international community did intervene meant all parties could profess to be engaged without any one being held accountable for the intervention’s futility.

For the refugees crowded into the Srebrenica enclave, the arrival of U.N. peacekeepers in April 1993 at least meant that their tenuous hold on life would continue. “The situation was terrible,” Fazila Efendic explained, “because we had to survive on whatever supplies the U.N. could bring in. But still we were very grateful to them. At last we were protected, we wouldn’t be overrun.”

In the spring of 1995, the faith in that protection was put to the test. Over the course of the war, the president of Srpska, Radovan Karadzic, had consistently flouted the ultimatums of the international community and grown openly contemptuous of its threats. Amid growing signs that outside powers, especially the Clinton administration, were determined to finally force a political solution in Bosnia, Karadzic chose to go for broke. He ordered his military commanders to cut off the flow of U.N. supplies into Srebrenica and an adjacent safe area. The ultimate goal, Karadzic wrote in a directive, was to “create an unbearable situation of total insecurity, with no hope of further survival or life for the inhabitants.”

In Srebrenica, the Serbs steadily ratcheted up the pressure on the Dutch U.N. Protection Force: turning back humanitarian supply convoys, denying re-entry to soldiers who’d left on leave, sniping at their observation posts. Then they launched their assault. As the Dutch soldiers stood down and the Serbs poured in on July 11, thousands of panicked refugees fled up the road to Potocari, searching for safe haven in the former battery factory now serving as the U.N. military compound. One of them was Fazila Efendic.

“It was madness,” she recalled. “People were crying, screaming, children were wandering lost. And from the hills all around, gunfire, explosions.”

In testament to the harsh fate the men and boys of the enclave expected at the hands of the Serbs, some 15,000 of them began to flee the valley on foot. Initially, Efendic’s husband, Hamed, and her 19-year-old son, Fejzo, joined in the exodus, but they turned back when they decided their odds of survival were better at the Dutch compound.

For the next three days, life for the refugees at the Dutch camp was one of unremitting fear. Before the Dutch soldiers barred the compound gates, several thousand of the luckier refugees took shelter in the main warehouse building, leaving the rest to huddle on the lawn outside. There, marauding Serb fighters picked out women to be raped, the occasional man to be murdered. All the while, the Dutch commander negotiated with Gen. Ratko Mladic, the Srpska military chief, for the refugees’ safe passage out of the enclave — but having already surrendered most of his battalion’s weapons and vehicles, he had little to bargain with. Finally buses and trucks were brought in to transport the refugees to Tuzla, 60 miles away. As the evacuation got underway, those “of age” boys and men who had stayed behind — more than 1,000, ranging from teenagers to men in their 80s — were separated from their families and put in different vehicles, ostensibly to be taken to “temporary detention centers.” Among them were Efendic’s husband and son.

“When we saw them separating the men,” Efendic said, “that is when we knew exactly what was to happen. The Dutch soldiers knew, too. Some of them were crying. Others just walked away. They couldn’t look for the shame of it.”

For reasons that would soon become clear, Mladic quarantined the Dutch on the Potocari compound for the next week. During that time, Serb fighters staged a hunt for the 15,000 fugitive men, killing an estimated 1,000 and capturing 6,000 more. As to why so many would surrender knowing the fate in store for them, that was at least partly explained by trickery: Driving the white U.N. vehicles and donning the blue U.N. helmets they had taken from the Dutch, the Serbs lured many out of the forest by claiming to be U.N. soldiers there to rescue them. Within days, all these captives, along with those taken at the Potocari compound, had been led to the killing fields. The Dutch soldiers could now be released. In a final act of mockery, General Mladic forced the departing Dutch commander into drinking a farewell toast.

To Radojka Filipovic, very little of this narrative holds true. She believes the number of Muslim dead is greatly exaggerated and that many of those who died were killed in combat or committed suicide — even that they were dispatched by fellow Muslims. As for the 6,000 graves in the Potocari cemetery, that’s highly suspect, too. “There are people buried there who died after the war,” she claimed. “And what of our people? There are still over a thousand Serb victims from this district missing from the war. Many believe some of those buried in Potocari are actually our people.” She gave a contemptuous snort. “This is their genocide.”

Robert Zomer doesn’t like crowds. And he felt especially uncomfortable standing with the crowd massed around the entrance to the old battery factory warehouse in Potocari on the morning of July 11, 2012.

“I’m very recognizable,” Zomer said, indicating his reddish-blond hair. “And there are a lot of people here who have a problem with me.”

The 30,000 people who converged on Potocari were there for the annual Srebrenica memorial ceremony, marking 17 years since the village fell. Zomer was one of the Dutch soldiers in the valley that day.

He stopped inside the doorway to the warehouse, where thousands of refugees once cowered, and took in the dreary, cavernous space, a bare concrete floor the size of two football fields enclosed by concrete walls.

“You can’t imagine what it was like,” Zomer said. “Everywhere people — screaming, crying, people being sick, some dying. And there was just nothing we could do. You could smell the fear. Before that day, I didn’t know that fear had a smell.”

He led the way along the north wall until he came to a low hole, a crude drainage outlet, presumably, leading outside. He pointed to a spot just to the left of the hole.

“There was a young woman sitting here by herself,” he said. “Crying, really hysterical, and I thought to comfort her. So I sat down next to her and placed my arm around her. I don’t know if she understood me, but I was telling her that it would be O.K., that everything would work out, when all of a sudden, a little cat came in through that hole.” Zomer chuckled. “It was so strange! But I picked up the cat, and I put it in the woman’s arms — I made her take it — and I said, ‘Here, now there is something that depends on you, now you have a duty to stay alive.’ ” He appeared lost in thought for a moment, then shrugged. “Well,” he said, “the odd things you remember.”

After his deployment in Bosnia ended in 1995, Zomer returned to the Netherlands, left the military and tried to forge a normal life. He married and had a daughter, but he found it hard to control his anger and ended up losing his first civilian job when he punched his boss. He eventually became a locksmith. “It’s a job you do alone, which I like,” he said. In 2011, Zomer’s marriage fell apart, and the following year he came back to Bosnia, where he had bought a 10-acre tract of forestland on the hillside above Potocari, less than a half-mile from the former Dutch headquarters.

“It’s much cheaper than Holland,” he said when I first asked him why he would return here. “And the weather is better.” He got a good deal on the property, because most of it fell within the old no man’s land between the Bosnian and Serbian front lines, and there was concern about land mines. He knows the mined areas to avoid, and on most days he takes his two dogs on long walks through the woods or heads down the hill to the old battery factory. He has discovered a break in the fence, and he likes to wander through the compound, largely deserted except on every July 11, by himself.

From almost the moment Zomer’s unit arrived in the area in January 1995, the most persistent question in his mind was what exactly they were supposed to be doing there. “To look after the refugees, O.K.,” he said, “but from a military standpoint, it made no sense. We were only given 20 bullets each, and our orders were to never shoot at anyone.”

His main assignment was to a forlorn observation post at the far southern end of the enclave, and he retains vivid memories of the march to Potocari as the enclave was falling.

“It seemed to go on forever. Mothers kept coming up to me and forcing their babies into my arms, ‘Please save my baby.’ So I would take these babies and carry them for a time and then just put them in one of the cars trying to move down the road.”

Zomer’s plan is to make his home on the hillside a kind of retreat for former military comrades who want to visit Srebrenica. “A lot of them worry that they will be attacked here,” he said. “They ask me, ‘But don’t they all hate us?’ By being here, I can show them that everything is O.K.”

Though he recognizes that he suffers from PTSD, Zomer seems almost willful in his efforts not to make a connection between his symptoms and the events that took place here. During the tense standoff at the compound, numerous refugees reported seeing women being raped, and several Dutch soldiers observed men being dragged off to an outbuilding, followed by the sound of gunshots. “I was inside the compound, so I didn’t know anything of what was happening outside,” Zomer said. As for the separation of the men at the buses, that was merely standard operating procedure. “It’s the same in any emergency,” Zomer explained, “women and children first.”

The July 11 ceremonies culminate each year in the burial of the dead. The night before, remains are brought in from the central mortuary in Sarajevo in a long convoy of trucks, the coffins then set out in neat rows in a smaller warehouse that was once the Dutch soldiers’ barracks hall. The summer that I attended, there were 520 coffins, all made of the same thin wood and wrapped in the same green Islamic burial cloth. Here and there, the tidy rows were broken by the presence of much smaller coffins, some no larger than footlockers.

Upon entering this room, Zomer stopped at the threshold, then leaned against the wall and stared at the coffins. “Of this, we knew nothing,” he said. “We only started to hear about it when we got back to Holland and people were saying, ‘You did a bad job, you let this terrible thing happen.’ But how could we have ever expected something like this?” He ran a hand through his close-cropped hair. “By the time you figure out you have to do something, it’s already too late.”

In early afternoon, several hundred men began carrying the coffins to the cemetery. A couple nearly tipped while being lifted, the pallbearers apparently thrown off by the lightness of their loads. The men found a rhythm, and as they carried their burdens across the road, other mourners lined their path to touch each coffin as it passed and mutter a prayer. As the ceremony began, Robert Zomer made for the break he’d discovered in the back fence and walked back to his home on the hill.

By outward appearances, the Srebrenica district looks to be slowly on the mend. Several small mosques have been built, replacing some of those destroyed in the war. The bullet holes and shell damage that once marked almost every building have been largely patched over. What is not readily observable is the radical demographic transformation that has occurred. Muslims, who made up three-quarters of the population before the war, are now a minority. That shift is largely explained by the fact that the district is now a part of the Republic of Srpska, which was allowed to remain in existence after the brokered end of the war.

Among the Muslims who have returned, the outspoken Fazila Efendic is the anomaly. Far more common is the case of Suleiman Mehmedovic, a 31-year-old laborer who lives with his wife and two children in a tiny apartment at the edge of the town of Srebrenica. Only 12 in July 1995, he left the enclave on a bus with his mother, but his father perished; his wife lost her father and all five brothers. “We just keep to ourselves,” Suleiman said of his life today. “I work alongside Serbs, and it’s O.K. We just never talk about what happened at all.”

To Milos Milanovic, a Serbian member of the Srebrenica City Council, that’s the best that can be hoped for. “There is never any discussion about these things, only arguing,” he told me. During the war, Milanovic, now 50, was a member of the Srspka armed forces and was present at the fall of Srebrenica. “It’s mostly propaganda,” he said of the numbers killed in the July 1995 massacre. “The Muslims have even presented our victims as their victims. They need to keep the death count high to present Serbs as the only criminals and to cover up their own war crimes.”

The annual July 11 ceremony is especially galling to Milanovic, and as a city councilman he has proposed that any municipal funds spent on that event be matched by a fund to commemorate Serb victims. “I think this is the only way we can start to get past the Muslim manipulations,” he said.

This historical revisionism is evident throughout the Drina River basin. Perhaps its most startling manifestation is a 25-foot-high Christian cross in Kravica, a village 10 miles west of Bratunac, erected to honor the “3,267 Serb martyrs” from the district who were killed in the war. While this figure doesn’t correspond to any figures in the authoritative “Bosnian Book of the Dead,” the placement of the cross in Kravica appears deliberately provocative: A few hundred yards down the road is a storehouse, where on the evening of July 13, 1995, at least 1,000 of the Srebrenica victims were dispatched with machine guns and hand grenades. There is no marker to indicate what happened there, and it has returned to its old function as a storage shed for farm equipment.

Postwar Bosnia wasn’t supposed to look like this — and for a long time it didn’t. In the fall of 1995, President Clinton’s special envoy to the Balkans, Richard Holbrooke, finally compelled the warring factions and their regional allies to the negotiating table. Because neither side had been militarily defeated, the Dayton accords laid out a novel solution: The Bosnia and Herzegovina government would be joined in a confederation with that of the Republic of Srpska, while each would maintain its separate status through an “inter-entity boundary line.”

As for just how this nonintegrated integration was to be achieved, Dayton laid out a comprehensive blueprint that included the establishment of a joint parliament, a co-presidency and a mixed judiciary. At the same time, there would be a thorough accounting of supposed war crimes, with those indicted made to stand trial. With the path eased by the generous response of the international community — billions of dollars in foreign aid earmarked for development and reconstruction — the hope was that the two communities would gradually come to regard the notion of parallel governments in such a tiny nation as a kind of embarrassing anachronism and would move toward full unification.

The linchpin in this whole plan was the creation of something called the Office of the High Representative (O.H.R.). The high representative eventually became the equivalent of a modern-day viceroy, with sweeping powers to appoint or promote any Bosnian official he or she deemed helpful to the peace process — and likewise to sack any who stood in the way.

“And it worked,” said an international diplomat serving in Sarajevo, who, because of the nature of his post, would speak only on the condition of anonymity. “This was an enormous challenge, because the war had been artificially ended, with no outright winners or losers, so how do you get these guys who’ve been killing each other to turn around and cooperate? The O.H.R. was the key, and if you look at how it operated in the early years, the locals quickly figured out that they had to toe the line or they’d get tossed out.”

Certainly the most remarkable development was a spirit of contrition within the Bosnian Serb community. In 2004, the Srpska government issued its own report on Srebrenica, fully acknowledging both the scale of the massacre and Serb culpability, with the Srpska president going so far as to issue an official apology to the victims’ families. Even if progress toward reconciliation lagged in other areas — the return of refugees to their former homes proceeded at a glacial pace; the worst of the indicted war criminals, including the architects of the Srebrenica massacre, remained at large — it was through such gestures that the schism running through society appeared to diminish.

Yet Dayton was built on a risky presumption. Because there was no internal mechanism to compel reconciliation, it meant the international community had to stay vigilant and resolute in imposing it. If the Bosnian war had revealed anything, however, it was that neither vigilance nor resolve was that community’s strong suit. By 2006, with the Bush administration mired in far more pressing foreign issues, the European Union had effectively taken over the running of the O.H.R. and displayed little interest in using its “soft power” to force reform. Unfortunately that coincided with the return to power in Srpska of Milorad Dodik, a former basketball player turned politician.

As prime minister of Srpska in the late 1990s, Dodik was regarded as a moderate and conciliatory figure, but he reconstituted himself as a Serb ultranationalist for his political comeback in 2006. Dodik repeatedly sought to scuttle whatever fragile power-sharing systems had been achieved and to portray the Serbs as the true victims of the war.

Why the about-face? Over the years, Dodik has been repeatedly investigated by the central government on allegations of corruption, and he has just as repeatedly suggested he is the target of a witch hunt by political enemies. “There’s very little margin being a moderate in Srpska politics,” the diplomat I spoke with in Sarajevo told me. “So when Dodik started getting into trouble, he turned to the race card.” The only thing standing in his way, the diplomat said, was the O.H.R. “But for the past eight years Dodik has constantly tested what he can get away with, and the message he’s received from the O.H.R. is that he can get away with anything.”

Leading up to the 2010 Srpska presidential election, Dodik’s government issued a new report on Srebrenica renouncing his predecessor’s conciliatory 2004 report. Not only had Srebrenica not been an act of genocide, Dodik proclaimed, but the number of victims was greatly exaggerated.

Rather than censure Dodik, the O.H.R. meekly urged his government to “reconsider its conclusions.” Instead, Dodik chose a memorial service in Bratunac on the day after the 15th anniversary of Srebrenica to assert, “If a genocide happened, then it was committed against Serb people of this region, where women, children and the elderly were killed en masse.”

The efficacy of this shift is clear. Running as a moderate in 1998, Dodik became prime minister only by forming a coalition with other political parties. Running as an ultranationalist in 2010, he received more votes than the nine other candidates combined.

In the quiet upstairs dining room of a restaurant in downtown Podgorica, the capital of Montenegro, I met a short, bull-shouldered man named Nenad. He bore a striking resemblance to a young Joe Pesci, the same olive complexion and intense, dark-eyed stare. Today he operates what he vaguely described as an “international security service,” which requires him to constantly shuttle among Serbia, Cyprus and Lebanon, but during the Bosnian war, he was in the elite special-forces wing of the Srpska Army, the so-called Red Berets. It’s a distinction he remains proud of; within minutes of our meeting, Nenad brought out his cellphone to show me pictures of his old red beret, carefully set on a pillow on the floor of his car. “I carry it with me everywhere,” he said. “It’s part of what defines me as a man.”

That pride seemed at odds with what he had agreed to talk with me about — his wartime experiences at Srebrenica. “When it comes to Srebrenica,” he explained, “the Serbian side can never admit what really happened there — ‘Oh, the numbers are exaggerated. There was killing on both sides’ — because then they have to face what was done in their name. But I think it’s important to tell the truth about that war.”

Despite Nenad’s willingness to talk, a precondition for our interview was that I not use his last name — “I’m worried about being called to The Hague,” he said, referring to the international war-crimes tribunal — and that no photographs be taken.

When the war began, Nenad was 19 and living in Gorazde in eastern Bosnia. Putting aside his hopes of becoming an engineer, he immediately answered the call to mobilization issued by Srpska’s president, Radovan Karadzic — “As a Serb, I was glad to do it” — and was dispatched to Bratunac for military training. He spent the next three years patrolling the Srebrenica siege line.

“It was almost like a game,” Nenad said, “a cat-and-mouse hunt. But of course we greatly outnumbered the Muslims, so in almost all cases, we were the hunters and they were the prey.” Aiding that hunt was a natural bait. “We needed them to surrender, but how do you get someone to surrender in a war like this? You starve them to death. So very quickly we realized that it wasn’t really weapons being smuggled into Srebrenica that we should worry about, but food. They were truly starving in there, so they would send people out to steal cattle or gather crops, and our job was to find and kill them.”

Because it was these same raiding parties out of Srebrenica that occasionally killed Serb civilians, Nenad and his comrades had a simple policy: “No prisoners. Well, yes, if we thought they had useful information, we might keep them alive until we got it out of them, but in the end, no prisoners.”

In fact, there was the occasional exception to this rule. With the Srpska soldiers’ no-prisoners policy, local Serbs who wanted revenge for the Bosnian soldiers’ raiding parties were being denied the opportunity. “The local people became quite indignant,” Nenad explained, “so sometimes we would keep someone alive to hand over to them just to keep them happy.” He then quickly added: “I didn’t do such things on my patrols — I was actually highly professional — but I know it happened quite often.”

By the time of the massacre in July 1995, Nenad said, he was no longer in the field but working at headquarters as an assistant to an officer close to Gen. Ratko Mladic. If that posting enabled Nenad to avoid any direct participation in the executions, as he claimed it did, it also placed him close to the inner circle where the decision to massacre was made.

“Within two days, we had a big problem on our hands,” he said, “because there were so many prisoners — about 7,000, all told — and what would happen if we just let them live? Then we would be left with snakes in our pockets, 7,000 more able-bodied men to wage war against us. So that was the solution. Everyone from the age of 15 was to be killed. It was a clear order that came in, and it was very specific: 15 on up. It came from the political side.”

When I asked whom he meant by “the political side,” Nenad offered that it was the Srpska president, Radovan Karadzic, along with the Serbian government of Slobodan Milosevic. “Everything was always coordinated with them.”

On the night of July 13, Nenad visited the small town of Kravica, where just hours earlier his colleagues killed more than 1,000 captives in the agricultural storehouse. “Because they used grenades, it was a real mess, just pieces of bodies and blood running everywhere. And now there was the problem of how to get rid of all these bodies.” He shrugged and gave a dismissive sniff. “Well, that was Engineering’s problem.”

The longer we talked, the more perplexing I found Nenad. He didn’t appear remorseful about his wartime actions, and even his description of the horrific scene at Kravica was presented in a flat, matter-of-fact way. He said that he had never spoken of these things to anyone before, and when I asked if there was any other reason that he was doing so now, a bitterness and sense of personal betrayal began to seep through.

“You know, I gave three years of my life over to this,” he said, “and at the end of it, I had nothing. I was actually hungry. Truly hungry, even close to starving sometimes. And what I saw was that it had all just been for the top men to line their pockets. I knew all the companies that Karadzic and the people around him controlled. Everyone else lost, but the generals and politicians, they all made millions off the war.”

Nenad expressed this last feeling with such vehemence that I had little doubt of his answer when I asked if, knowing what he knows now, he would do it all over again. I was mistaken. “Of course,” he replied without hesitation. “If again Serbia is attacked, of course I would fight.”

On a cold day this past February, I visited Robert Zomer at his home on the hillside above Potocari. He’d done a great deal of work on the house in the year and a half since I first met him and had recently taken up raising goats; two were born on the morning I showed up.

At our first encounter, I was struck by how determined Zomer had been to explain away the horrors of Srebrenica. But now that defensive facade had fallen away. Last year, Zomer slipped into a deep depression, one that led him to return to the Netherlands and check into a military psychiatric hospital for two months. While there, he underwent art therapy and was taught relaxation techniques, but his treatment didn’t include much in the way of talking about the events of Srebrenica. Left largely to his own devices, Zomer arrived at a rather novel explanation for the cause of his PTSD. “It wasn’t from what happened here,” he said. “It’s from when we returned to Holland, and everyone there said we had done a bad job.”

On a more hopeful note, Zomer’s 14-year-old daughter visited him in Bosnia last summer, and he said he had hosted about 50 Dutch veterans of Srebrenica. “They’re always very nervous at first,” he said. “But they stay with me, and I take them up to see our old outposts, and after a day or two, they start to relax.”

Most days, he spends several hours communicating with other veterans on a closed Facebook page. It seems to act as a kind of therapy for him, and Zomer believes he’s helping many of his former comrades sort through their complicated feelings about Bosnia. When I asked if he thought some of them also had psychological issues as a result of their tour in Srebrenica, he replied: “All of them. Some don’t realize it yet, but all of them.”

At the end of our meeting, Zomer walked me up the muddy hill to where my car was parked. He had a new extremely friendly puppy, and I asked what had become of the two dogs I remembered. “Gone,” he said, shrugging. “One was hit by a car and the other poisoned. Dogs don’t last too long around here.”

Soon after, I met again with Amor Masovic, the mass-grave hunter, this time in the cafe of the Hotel Europe in Sarajevo. He had news for me. When I last saw him, in the summer of 2012, he talked about the Serb acting out of “half-conscience” who had revealed a grave site, but now there was another. Masovic described several clandestine meetings he had in 2013 with a Serb in northern Bosnia, which led him to a mass grave in Tomasica.

“It was a site we had excavated twice before,” he said, “and we’d found about 30, but [the informant] said, ‘Go back and look again.’ ”

Hundreds of those bodies have now been exhumed. Because the grave is so deep, about 25 feet in places, and the soil mostly clay, there was remarkably little decomposition among the Tomasica victims, their intertwined bodies preserved to form a nightmare tableau.

Masovic suspected that in Tomasica he had most likely found the last large mass grave in Bosnia. I imagined this would give him some grim satisfaction, but Masovic told me he was increasingly dispirited, both by his labors and by the pace of justice in Bosnia. In the 18 months since our first meeting, a string of convicted Serb war criminals had been set free on legal technicalities, while others had their sentences reduced. In The Hague, the trials of the principal architects of Srebrenica, Radovan Karadzic and Ratko Mladic, continue at a desultory pace, although the two have been in custody for six and three years. No verdict is expected for either man until 2015 at the earliest. (By comparison, the Nuremberg war-crimes trials of the Nazi leadership lasted 11 months.)

“Sometimes I wonder what it’s all for,” Masovic said, looking even wearier than I remembered, “if so few are ever brought to justice.”

By coincidence, on the same day that I met Masovic, the downstairs conference rooms of the hotel had been taken over by the United States Agency for International Development for a signing ceremony fostering greater economic cooperation between Bosnia’s two communities. That ceremony came on the heels of the agency’s having just kicked off what it called the “largest reconciliation program attempted in Bosnia and Herzegovina,” which would include a new series of initiatives and would add another $4.2 million in aid to the large amounts the agency has disbursed in Bosnia since the end of the war.

Unfortunately the spirit of the ceremony was somewhat marred by an episode days earlier in the town of Visegrad in eastern Bosnia. One of the first areas to be subjected to the Serbs’ ethnic-cleansing campaign, the Visegrad district was completely emptied of its Muslim population during the war, but some of the returning survivors had erected a memorial in the town’s cemetery to honor the “victims of the genocide.” In late January 2014, local authorities determined the memorial to be inflammatory (there “is no proof of verdict about genocide in Visegrad,” the mayor announced), and the offending word was ordered removed. While 150 Srpska police officers clad in riot gear stood guard, a municipal worker with a power tool methodically ground “genocide” from the stone.