KNOXVILLE, TN — The nameless teenage Mexican immigrant killed in a drug skirmish could hardly have imagined that this would be his final resting place. His knees are drawn up into the fetal position; his body appears almost mummified, the skin a leathery brown merging with the fall leaves underneath. The sloped woods around him hum with cicadas. All is deathly peace in this hillside spot. A few feet away, a leg lies perfectly camouflaged in the brush, given away only by crimson strips of flesh still clinging to it.

Under a row of trees nearby, a woman lies on her back, half rotted away, her arms outstretched in a frozen gesture and her hair lying in a molted mat around her skull.

Three yards further on, a raw foot protrudes from a body bag. As it is lifted, a mass of maggots is suddenly scattered by the sunlight. The body is pale gray-green, quivering with the larvae feeding on its back, which has melted into a liquefied surface as soggy as a bar of soap. The sugary porcine smell in the air is unmistakable.

Researchers at this facility have been observing bodies decay in order to uncover the secrets of death.

Under spice bushes and saplings, little piles of bones lie quietly decomposing. The setting all looks rather pastoral, except for the two rusting cars and cases of scientific instruments nearby. Cemetery it may be, but conventional it is not.

In life, the Mexican boy didn't know the other two dozen people scattered around this gated two-acre copse belonging to the anthropological research facility at the University of Tennessee. But in death, they have been united by an unsettling experiment. Since 1977, researchers at this facility, located on the edge of the university medical center in Knoxville, have been observing bodies decay in order to uncover the secrets of death. It is the only such experiment in the world. Bodies are buried, left in the open air, covered with canvas (which encourages maggots to go at them) or entombed in one of the rusting cars to test how decomposition rates vary.

In the summer heat, for example, a body can go from flesh to bare bones in a mere two weeks. Murray Marks, a forensic anthropologist, gestures at the wrecked cars. "Inside cars, the bodies rot faster," he says quietly as we pick a path gingerly through denuded tibias, femurs and mandibles. "Of course, the police often find bodies in the trunks of cars. A car, you see, is much hotter than underground. It accelerates the timetable of decay. Our work is really all about temperature."

"Death is a process, not an event," he adds softly. "It's beautiful if you consider it calmly."

We stop by a bloated woman, her body turned a scabrous orange and cranberry red, her ankles thinned almost to the bone. "Eventually, we want to make a complete atlas of decomposition," Marks says. "We take digital photographs of the process every three hours, We want to know exactly what happens when your body rots."

We pause to stare at the woman's perfectly preserved hand clenched into an eternal fist. "Death is a process, not an event," he adds softly. "It's beautiful if you consider it calmly. It's Nature at work. I mean, I love that woman's hand. I often stop and admire it." He reaches down with his own hand sheathed in a surgical glove and strokes the mortified knuckles. "To me, there's nothing horrific in all this. Nothing whatsoever."

Higher up the slopes, there are other bodies. Three men embalmed by a local funeral home are spread in a row, their well-preserved flesh noticeably thicker and tougher. Marks stoops to examine their dark orange toes. It seems that the raccoons have sneaked in again, and they have a fondness for toes. For this reason, another more recent arrival sprawls protected behind a wire cage. It's a middled-age [sic] woman who has begun to bloat slightly. Honeybees swarm her mouth and nostrils, searching for the eggs that blowflies like to lay in the body's dark cavities. To me, this intense insect commotion adds a note of horror, but Marks insists that the interaction between insects and corpses is one of the crucial areas of his research.

"Insects are a vital key for us," he explains. "More than anything, we're trying to establish the exact time since death. We can determine that often by seeing how fat the maggots are or what stage the insect cycle is at. Insects are our friends. I especially love maggots. They're information bombs!" The Knoxville facility, he goes on, is the only place in the world where the cadaver-insect symbiosis can be observed through all its cycles. Every murder, he says, is simultaneously an entomological detective story.

He touches my arm gently. "Are you all right?"

I say that the stench is getting to my stomach.

"It gets to me, too, sometimes," he admits. "But as it happens, we're studying the stench, too."

He points to a small box that has been suspended above one of the bodies. It's called an electronic nose. Inside it lie 32 sensors that ingest the various malodorous compounds given off by decomposition. These compounds, which have gothic names like cadaverine and putrescine, are collected in a vial and from there fed into a gas chromatograph that identifies them. Since putrefaction follows a predictable cycle, a kind of olfactory time chart can be deduced from these smells, helping law-enforcement officers and forensic experts determine when an unidentified corpse might have met its end. It's all part of establishing a minutely dependable chronicle of death, which may soon make committing the perfect crime a forbidding prospect.

"We can't necessarily identify a corpse with this new research," Marks says. "But we can recover its history, the secret of its death. We can reach back and see how long it's been lying there. Surprisingly, we know very little about death. It's the ultimate mystery, because we never really see it close up. Except here."

THE DEPARTMENT OF FORENSIC ANTHROPOLOGY is housed in the bowels of the university's Neyland Stadium. "Home of the Vols" says the pale orange sign towering over this dreadful cousin of the Coliseum, making it perfectly clear to the scientists crammed inside it that football is far more important to Knoxville than forensics. Inside the dark, ovular corridors that follow the walls of the stadium, spic-and-span labs are filled with skeletons, trays of vertebrae and skulls resting on little colored cushions. In one room, huge casseroles filled with fully decomposed remains from the nearby woods are being boiled clean in detergent.

The department's unofficial in-house identification badge features a skull with two crossed sabers. It's one of the morbid touches favored by the program's founder, Bill Bass, who at 73 is now a professor emeritus. Of the 61 specialists certified nationwide by the American Board of Forensic Anthropology, one-third were trained by Bass.

In an average year, the hills and streams of Knoxville alone yield about 40 to 50 unidentified bodies.

He's the founding father of the field. His work at Knoxville has influenced more than just scholars. In 1994, Patricia Cornwell published a novel inspired by Bass and his research. She titled it "The Body Farm," lending the facility a ghoulish sobriquet. "I rather like the term," says Bass in a soft Southern lilt. "I think it says it all. Though some of my colleagues consider it tasteless."

Bass came from the University of Kansas in 1971. "Back then, there was almost nothing 'in the literature about decay," he recalls. "I hadn't thought about it much either, because in Kansas most of the bodies are dry, post-decay specimens. But Tennessee is hot and moist, with twice the population per square mile of Kansas. That means a lot of active-decay corpses!" (Today, in an average year, the hills and -streams around Knoxville alone yield about 40 to 50 unidentified bodies, some of which end up at the farm.) Bass asked the dean for a plot of land in which to strew some bodies — mostly cadavers of homeless men — and was given a parcel on a university-owned pig farm nearby. The present site was opened in the early 80's and contains for the most part the remains of people who have willingly bequeathed their bodies to science, mixed with a smattering of deceased and unclaimed undesirables.

In 1977, Bass's ignorance was brought home to him when he identified a well-preserved corpse with a gunshot wound to the head as being merely one year old. There was, he reasoned, flesh still hanging on the bones, much of it still noticeably pink. In fact, it was the body of William Shy, a Civil War colonel killed in battle and buried in a sealed lead coffin. "Well," Bass muses, "I only missed it by 113 years! It made me realize how totally clueless we were about death. The only way to do it, I realized, was to let a body rot and watch it."

With the decay evidence, Bass proved the body had been killed a week before Rogers had tried to burn it.

Since then, Bass has used his research at the Body Farm to crack some horrific crimes. On July 21, 1997, for example, the Tennessee Bureau of Investigation called Bass to the house of one Matt Rogers in Union County, 30 miles from Knoxville. Rogers's wife, Patty, had been missing for two weeks, and agents had just found a trash can filled with charred bones.

A cool Rogers claimed they were goat bones. "Well," says Bass, "the guy did raise goats, so we had to take a closer look." Identifying the bones as human, as it happened, wasn't hard, nor was piecing together poor Patty's disassembled skeleton. Bass then uncovered gunshot residue on the skull and proved that, according to the decay evidence, the body had been killed a week before Rogers had tried to burn it. Such data is important in criminal cases, as it was in this one, because it can demolish a seemingly watertight alibi. "I think he carried her around in his car for a week, but we never found the car," Bass says. "It's always bothered me that we never found that car — it remains an annoying secret. I'm still obsessed about it."

Bass similarly used his Body Farm insights to unravel a would-be "perfect crime." On Dec. 16, 1993, the Mississippi police were called to a cabin in the small town of Summit. Inside were the decomposing bodies of Darryl Perry, 24; his wife, Evelyn Ann, 20; and their 4-year-old daughter, Krystal. The immediate suspect was Darryl's stepfather, Michael Rubenstein, who, according to the district attorney, appeared to know telling details about the three deaths. It was Rubenstein himself, however, who made the 911 call — and nothing directly linked him to the crime. He claimed to have driven 120 miles from New Orleans just to make a family visit. He also claimed to have visited the cabin on Nov. 16 and 27 and to have found nothing amiss.

When the district attorney brought charges against Rubenstein in 1998, he called in Bass to study the crime-scene photographs. "I saw at once," Bass remembers, "that there were empty pupal cases left behind by maggots as they turned into flies. So I knew that at least one fly cycle had taken place. That takes at least two weeks." From his observations at the Body Farm, Bass also knew that autumnal decomposition, with cold nights, is much slower than summer decomposition — and that since the bodies were much decayed, the time of death was probably at least 35 days. He estimated death at mid-November, that is, at exactly the times of Rubenstein's visits to the cabin. Bass's evidence was enough to sentence Rubenstein to death in a Pike County, Miss., courtroom earlier this year. As Bass puts it, "The guy had an alibi for the beginning of December — but not for the middle of November."

As Bill Goodwin, the Pike County district attorney, concluded after the trial, "Without Bass's testimony, I think there's a good chance they'd have let Rubenstein go."

Bass chuckles with satisfaction. "I liked that case. The pupal cases nailed him, all right."

Forensics can't solve every crime, of course. "Murder is still one of the easier crimes to get away with," says Richard Jantz, another anthropologist at the facility."We have dozens of unidentified murder victims in our labs. I have a 12-year-old girl in here now we can't make head or tail of.

"Murder is still one of the easier crimes to get away with. We have dozens of unidentified murder victims in our labs."

And nationwide, hundreds of enigmatic bodies show up every year. You have to remember that our understanding of dead bodies is still in its relative infancy."

To help spread their forensic knowledge, Body Farm scientists work closely with law-enforcement officials. "The F.B.I. began coming here for instruction this March, and we do hope to have a fruitful relationship with them," Jantz says. "We've set up courses for their field teams, so they can see what crime scenes with real decomps look like. But we all have a lot to learn."

As for preventing crime, Jantz points out. that the police could "forensically map" the population at large. far more exhaustively than it actually does: "I mean, we could fingerprint bullets, for example — give each one an identifying mark. But will gun manufacturers agree to it? There's no political will to push this to the limits, because people are scared of a police state. Do we really want to live in world without any secrets? Maybe not. But it could be done."

MEANWHILE, THE TECHNIQUES FOR RETRACING the evolution of a murder are getting ever more refined. Take soil samples. As bodies decompose, they leak five fatty acids into the ground beneath them. Each day after death, the various profiles of these acids will vary. Analysis of them can reveal the time of death, as well as pinpoint exactly how long any given body has been lying in a particular place. The soil can also reveal the presence of a corpse, even if the body itself has been removed or destroyed. The "stain" left by a body's volatile acids, which also suppresses plant life around it, can last for up to two years, leaving a kind of phantom fingerprint in the earth.

Another promising area of inquiry has to do with the smells emitted by rotting corpses.

Thus, soil, like maggots, becomes an "information bomb," and the dead can be reconstructed (if not resurrected) long after they have disappeared physically. In a recent case in Florida, a prison inmate confessed to a cellmate to having raped and murdered a woman he had abducted from a convenience store.

Police couldn't find a body, but soil samples in several sites named by the inmate proved that one had indeed been there. The samples of earth saturated with bone minerals and fatty acids were enough to convict him.

Another promising area of inquiry has to do with the smells emitted by rotting corpses. Jennifer Love, an anthropologist at the Body Farm, has been studying death smells in association with the Oak Ridge National Laboratory. The goal of the project is to develop techniques to estimate time since death during the early stages of decomposition, specifically targeting the breakdown of soft tissue.

Love thinks her research will transcend the time-of-death question. "Once we understand the composition of decay odor, we can develop better synthetic sprays to train cadaver-hunting dogs," she says. "Eventually, we can also design hand-held instruments that could potentially sniff out corpses at crime scenes by picking up the aromatic compounds of decay odor."

Other areas still to be explored are DNA extraction from cadavers and putrefaction in different contexts — from inside plastic bags, say, or underwater. "We know little about these two areas," Bass says. "How does a body rot in water? I'm very excited, too, about experiments with the plastic bags.

Other areas still to be explored are DNA extraction and putrefaction in different contexts — like inside plastic bags.

It's fascinating." A recent grisly find in a Minnesota cornfield revealed two bodies wrapped in plastic that had remained well preserved in direct sunlight. "Why?" Bass grins. "We have no idea."

Jantz shares Bass's enthusiasm. "In the near future," he says, "we will rely more heavily on biochemical and molecular evidence. I think you will see forensic-anthropology applications along the lines of extracting DNA from bones, hair and teeth. In addition, determining the victim's sex and ethnic background from small pieces of bone or other biological residues will become more common."

In addition, studies of how changing social conditions — like improved nutrition and greater life expectancy — have affected the human body may soon allow experts to make very accurate estimations of the date of a skeleton's birth. "We will understand variation in skeletal biology in the American population much better than we now do," Jantz says. "In the end, what we do is work backward from this kind of knowledge to make inferences about a specific set of bones." Even a pile of bones, in other words, will be made to speak.

In one recent case, bones were made to do just that. In August 1997, Murray Marks was called to an abandoned house outside of Knoxville where a 21-year-old woman had been found floating in a septic tank on the property. Marks and a local pathologist pored over the bloated, maggot-infested corpse and estimated time of death to be between four and seven days. "When we got there, the body was headless," Marks says. "The head had sunk to the bottom of the well, from where we had to fish it out." The cranial bones were confusingly scattered in refuse and once recovered had to be painstakingly reassembled.

"Every wound tells a story. We've learned a lot about head traumas from the mission skeletons, and a lot about scalping."

Marks, who is a specialist in facial reconstructions, pieced together not only the dead woman's face but also the trauma wounds of the skull, which established a "blunt force instrument" as the killing weapon. "In this case," Marks goes on, "we used all our insights into maggots, fly cycles, bloating and bone reconstruction to piece together this dead person.

It was pretty humbling, I have to say, to have that woman's skull in my hands, knowing that I was unraveling this dreadful secret — that I was solving the timetable of her death."

While at the forensic anthropology department, I visit a group of graduate students. One of them, Corey Sparks, has made a special study of the trajectory of bullets as they enter and leave the body. Standing by a skull held delicately in place by clay clamps, he shows me how digital scans are taken as the skull is rotated minutely, degree by degree. The computer image shows the bullet holes in bright blue and the trajectory as a yellow line. Sparks is currently involved in a 15-year-old murder case in Georgia in which a man claimed to have accidentally killed his wife while cleaning his rifle.

"But," says Sparks, smiling broadly, "we scanned her skull, which is sitting in a fridge in Memphis. And we found that the bullet had to have come from directly above her. 'So we proved it was murder." The digital scans, he adds, make for more palatable objects in court than a rotting head — as well as being, according to Sparks, the first digital forensic testimony ever used.

In another research project, Sparks is studying the century-old remains from a Spanish mission in Texas. Many of these colonists, he explains, were killed in Indian raids. "Every wound tells a story, and we've learned a lot about head traumas from the mission skeletons," he says. "We've learned a lot about scalping."

Back at the farm, Murray Marks shivers at the sight of a spider hanging from a large web obstructing our path.

"Frankly" he sighs, "I'm more scared of spiders than I am of dead bodies."

We lock the gates behind us, admiring for a moment the crenelation of razor wire and a shed piled high with salt. He tells me they have had only one skull stolen in 25 years. I ask him then if he thinks criminals are wising up to the new techniques in demystifying death.

"A decomp is a thousand times more interesting than a skeleton. Skeletons are just boring eye-candy."

"They are, yes. They're beginning to cut bodies up more and make more of an effort to dispose of them. But fortunately for us, most murderers are still pretty dumb."

We breath the sweet stench for the last time. "You get used to it," he says. "To me, a decomp is a thousand times more interesting than a skeleton. Skeletons are just boring eye-candy."

Later, I ask Bass himself if anything in his dealings with the dead had ever disturbed him.

"Not really," he says without missing a beat. "I hate death itself. I hate funerals. But dead bodies? Then again, as my wife points out, I have a very poor sense of smell."