Worn and muddy, the passports and identification papers rustle in the hot wind of a Kosovo summer, stuck gently amid the roses scattered on piles of fresh red earth.

There are 21 booklets in all, one for each of the bullet-riddled corpses that lay below. The ethnic Albanian victims were apparently sprayed with gunfire as they cowered in a gully three yards away. Fifteen were members of the same family; six were less than 10 years old when killed; the youngest wore diapers.

A third of a mile away, perched on a hill above the red-tile roofs and carved-wood gates of this typical Kosovo Albanian village, Detective Superintendent William Gent of New Scotland Yard huddles under a sweltering tent. He is poring over evidence, preparing to unearth the bodies below.

Passports, jewelry, bloodstained clothing and other personal items will help identify victims. Eyewitness accounts and spent bullets will aid in determining who did the killing. Autopsies will confirm the ages and cause of death.

Gent's 18-member team--along with a half-dozen other groups from the FBI and other Western law enforcement agencies--are at ground zero in the U.N. war crimes tribunal's effort to build a case against Serbian and Yugoslav officials for atrocities committed against ethnic Albanians in Kosovo, marrying the established discipline of criminal investigation with the uncertain efforts of war crimes prosecution.

The investigators are using the same basic forensic techniques that they would at any murder site, except that most murder sites don't have scores of victims. Most victims aren't buried on top of each other in remote fields, charred or decayed beyond recognition. And most killers don't come in uniformed squads, armed with machine guns and hand grenades.

"At its core, it is exactly the same as any other standard, forensic crime scene investigation," Gent said, standing 100 feet from a burned farmhouse that held seven executed ethnic Albanians. "The difference is the size of the crime scene, the sheer number of victims, and the brutal, brutal way they were killed. . . . Everybody here is experienced in dealing with murders, but no one has experience dealing with anything quite like this."

Celina is at the epicenter of what is proving to be the heaviest concentration of mass graves in Kosovo. More than 50 bodies, mostly women and children, have been exhumed so far from eight grave sites in this 3,000-person settlement, and investigators expect to find as many as 50 more. Hundreds of others have been unearthed from the clay soil in the surrounding area, and U.N. officials suspect thousands more will be found.

"This whole village is a crime scene," said Keith Martin, one of the tribunal's field investigators.

The bodies from Celina are transported to a special U.N. pathology center a few miles north in an abandoned granary. The morgue is a truck-size freezer that held about 20 corpses last week; there was room for 30 more.

Inside the decrepit granary, pathologist Jack Crane of Queens University in Belfast and his team perform autopsies at the rate of one per hour, 10 per day. The power needed for the morgue and an X-ray machine, used primarily to locate bullets and their paths, comes from a generator. Eight black, zippered body bags were piled around the stench-filled room with two others on gurneys; anthropologist George Maats was sawing through the leg of a young girl to determine her age, much like counting the rings of a tree.

Crane, who has conducted autopsies from Bosnia to Northern Ireland, said the severe decomposition of the Celina victims provides the greatest challenge for a pathologist. Bullets are perhaps the most important pieces of evidence, he said, because the team's ballistics experts can link certain types of bullets with Serb-led Yugoslav troops and can use their trajectory to determine how the victims were shot.

The shooting in Celina began on March 25, the day after NATO airstrikes against Yugoslavia began. It was cold but sunny, after days of icy rain. Yugoslav army soldiers and Serbian special police stormed the village that afternoon, survivors say, executing some against stone walls and hunting down others in the woods nearby. The killing continued into the next day, and those who were not slain fled into the eastern hills or to the western mountains toward Albania.

Among the dead were more than 20 people, including 15 members of the extended Zeqiri family, who made their flight down a streambed and into the gully on the first day. The bare trees could not hide them: Three Serbian policemen armed with AK-47s just up the hill killed members of the group as many crouched on their hands and knees for cover; an older man was picked off trying to escape up the hill.

Six hours later, another Zeqiri and four other people were caught trying to creep into the same woods. This time soldiers and police lined them up against the inside of a concrete shed, killed them and burned the bodies along with an Opel sedan. They also shot the Zeqiris' shepherd dog, whose corpse lies chained under a small wood shed.

"They were yelling to us that we were KLA [Kosovo Liberation Army, the ethnic Albanian separatist group], that we were terrorists," said Nustret Salihu, 23, who escaped the killing by hiding under a stairwell. "They told them the truth, that none of us were KLA. That's when they started shooting."

The final story of what happened in Celina will come not just from autopsies and ballistics tests, but from witnesses like Salihu. Firsthand testimony will go a long way toward proving whether the dead were innocent victims of war crimes, or casualties of war.

"That's vital to any criminal investigation, and this is no different," said Martin, the tribunal's liaison to the Scotland Yard team. "Witnesses are one of the keys to our case."

Proving crimes committed during something as inherently lethal as war is a tricky business. In general, Martin and other tribunal officials said, purposely killing any civilian who has not actively taken up defense of an area is a war crime.

Thus, investigators are looking particularly hard at clothing, witness statements and other evidence to determine if victims were members or allies of the KLA.

In the case of Celina, the point may be moot; Gent said there is no evidence of KLA affiliation or weapons among the victims. Most were women and children.

"What we are looking to try to prove for [the tribunal headquarters at] The Hague is that in any given case, there were women and children that were mercilessly killed for no reason at all," Gent said. "If we can establish how people died, and establish that they were ordinary women, children and men going about their lives, that will go a long way to proving that crimes occurred."

CAPTION: Investigators exhumed these bodies from a mass grave in the Kosovo village of Celina on Thursday. Most of the dead were women and children.

CAPTION: These photographs of the bodies exhumed Thursday were taken by a survivor of the murders. Villagers gathered recently to examine them.

CAPTION: Hazir Zeqiri walks away from the site where more than 20 bodies were exhumed. Fifteen of the victims were members of his extended family.