麻豆传媒

JENNIFER SYNSTELIEN emerges from the tool shed wearing a knee-length plastic apron, surgical face mask and thick latex gloves. Unfazed by the smell of death wafting through the warm autumn air, she kneels next to a decomposing corpse. Her practised hands wave at hovering flies as she opens the chest cavity and pokes around for the heart with long, stainless steel forceps. It鈥檚 gone liquefied 鈥� after a month of decay. 鈥淎t this point, I don鈥檛 know if there are any organs left,鈥� she says.

So begins a normal day at the Body Farm, a gruesomely remarkable research facility where 20 or so bodies at a time rot in the open air in the name of forensic science. Synstelien is a forensic anthropology graduate student from the University of Tennessee, and is working with Arpad Vass, a biochemist at Oak Ridge National Laboratory. For more than a decade, Vass and his students have used the corpses to study how time and nature treat the human body. They have discovered ingenious biochemical ways to measure the time since a person died, and have been instrumental in solving upwards of 100 murder cases. And now Vass鈥檚 team has uncovered a whole new set of biochemical markers that will allow investigators to pin down the time of death even more precisely, perhaps to within an hour.

Based at the University of Tennessee (UT) at Knoxville, the 20-year-old site is officially called the Anthropological Research Facility. It is the legacy of UT鈥檚 William Bass, a pioneer in forensic anthropology. His exploits in identifying remains and fingering suspects inspired Patricia Cornwell鈥檚 1994 novel The Body Farm 鈥� a name that has stuck, much to the chagrin of its staff.

As we drive to the site, Vass explains the layout. Over the years, more than 300 bodies have decayed on the 3-acre patch of wooded hillside just across the Tennessee River from downtown Knoxville. Arrayed in settings resembling crime scenes, the bodies are tucked in the back seats and trunks of rusting cars, hidden beneath underbrush, buried in shallow graves, laid out naked in the grass, or simply left in the body bag they arrived in. Vass says his work is not about death but about science. Each corpse serves as an experiment, a scientific stand-in for someone who is, or might one day become, missing or murdered. 鈥淲hat you鈥檒l see here is what鈥檚 going to be happening at a real crime scene.鈥�

There are four stages of decomposition after death: enzymatic liquefaction of cells, bacterial decomposition of tissue, drying of the skin and remaining soft tissue, and then skeletonisation. These processes occur in the hours, days and months after death. The rates depend on environmental conditions, especially temperature and humidity. 鈥淚n the heat of a Tennessee summer, I鈥檝e seen the progression from fresh body to bare bones in a mere two weeks,鈥� says Vass.

In the 12 to 24 hours after someone has died, visible changes in the body allow a medical examiner to give an accurate enough estimate of time since death. But when corpses are days or weeks old it becomes more difficult because the complex chemistry of decay takes over and, until recently, no one understood much about it.

Vass and I pull up in the parking lot behind UT鈥檚 Medical Center, where the morgue has become a way station for cadavers destined for the Body Farm. Ignoring 鈥淜eep Out鈥� and 鈥淣o Trespassing鈥� signs, we approach a chain-link fence, which has been topped with razor wire to keep out vandals. Ever since tricksters attempted to steal some skulls one Halloween, the site and its silent inhabitants have been under 24-hour surveillance.

Life and death

Swinging open a chain-link gate, and then a higher wooden one, Vass ushers me in. What鈥檚 inside is not for the squeamish, he warns. But there鈥檚 no way to prepare for the onslaught of sights and smells. A skeleton, part of its rib cage clad in leathery skin, gapes face-up through honeysuckle vines. A plastic body bag quivers in the sunlight as masses of maggots feast within.

Vass leaves for a moment to warn his colleague, Synstelien, that we鈥檝e arrived. 鈥淲e don鈥檛 see a lot of live people out here, so I don鈥檛 want to scare her,鈥� he whispers. This gives me a moment to adjust to the sickly sweet stench: a melange of rancid meat, eggs and butter intertwined with honeysuckle. Moments later, Vass signals me to join him and Synstelien.

Behind us, under a large oak tree, is the desiccated corpse of an old man whose few remaining hairs cling desperately to a barren skull. Close by, a once-plump woman is reduced to overlapping folds of dried, beet-red skin. Because these two bodies look very similar, medical examiners might think they died on the same day, explains Vass. He, on the other hand, could tell you they died weeks apart.

Vass鈥� research into the chronology of death began in the late 1980s while he was a graduate student at UT, studying under Bass. With the help of the Body Farm鈥檚 subjects, Vass went in search of 鈥渄eath markers鈥� that would indicate time since death (TSD). He first tried to identify the myriad of bacteria that come and go as the body decays, but soon gave up because he found thousands of species. 鈥淚t was out of control,鈥� he says.

So Vass turned to the soil beneath a corpse. As a body decomposes, volatile compounds are released, and as organs liquefy, complex fats and proteins are broken down and seep into the ground. Vass spent four years prying apart and quantifying the unique chemical profile of the dead. By 1991, he鈥檇 worked out two methods for dating remains.

The first tracks the ratio of five volatile fatty acids, the breakdown products of fat and muscle, which can be sampled from any material around a corpse, including soil, vinyl, carpet, clothing and body bags. With each day that passes after death the concentrations of all five rise and fall, but their ratios vary systematically as long as there is soft tissue 鈥� skin and organs 鈥� still on the body. A similar technique looks at the ratios of seven inorganic compounds, including sodium, potassium and calcium, which leach from bones into soil. This turns out to be an accurate marker in the absence of flesh, which usually disappears a few weeks after death.

These ratios are the same for everyone because we all have the same basic chemical blueprint, and each body constituent, such as fat and muscle, has a characteristic breakdown pattern. The only variable is weight, which Vass estimates using information from a driver鈥檚 licence, a person鈥檚 clothing and the size of the skeleton. With that he can standardise the varying concentration of fatty acids and bone minerals. The more accurate the weight estimation, the more accurate the TSD determination. 鈥淚f you only have the skull,鈥� Vass notes, 鈥渢hen it鈥檚 pretty hard.鈥�

Using the ratios, Vass creates a set of tables that correlate the decay markers to TSD at different temperatures. Combined with temperature data from the National Weather Service, the chemical 鈥渟ignatures鈥� let him estimate TSD with an accuracy of two days for every 30 days of decomposition. He can do this for up to seven years after death in any temperate climate.

The technique was first put to the test in 1992, when Bass returned from Georgia with soil from a case he had not been able to solve using traditional methods. Vass estimated the TSD, but the case remained unsolved because the body was never identified. Soon after, little bags of dirt from crime scenes across the nation started arriving in the lab. Eight years later, Vass is still busy consulting with FBI medical examiners and local police, bringing the Body Farm鈥檚 grim harvest of knowledge to bear on baffling and high-stakes cases. 鈥淚 always get the really weird ones,鈥� admits Vass, whose approach is now widely accepted by forensic scientists.

In a 1994 Florida trial, soil analysis by Vass became the damning evidence that convicted a man of murder, even though the victim鈥檚 body was never found. Vass says a prisoner bragged to his cell mate that he abducted a woman after she left a convenience store and then raped and killed her. The prisoner also revealed that an accomplice had helped him bury and move the body several times. The cell mate told the police, who tracked down the conspirator and persuaded him to cooperate.

They sent Vass soil samples from several potential temporary grave sites. By analysing the minerals and fatty acids in these samples, Vass found clear evidence of a dead body in all but one of the sites. The amounts of the chemical markers confirmed they came from a large mammal, and the lack of fur or animal bones convinced the jury that the mammal was a person. The suspect received a life sentence.

Not every case ends so neatly. Vass tells me about a man in Ohio who killed his wife and hid her in the trunk of his car. To mask the odour, he sprayed the body with insecticide. Several days later, he dumped her in a field, where she was eventually found. By using insecticide, the husband unwittingly prevented insects and microbes from digesting the body. 鈥淪he didn鈥檛 rot at all,鈥� says Vass. 鈥淪he was perfectly preserved and I couldn鈥檛 do a thing.鈥�

Vass frequently teams up with forensic entomologists, who use maggot and beetle ecology and behaviour to date remains. Neil Haskell, a 30-year veteran in entomology at Saint Joseph鈥檚 College in Rensselaer, Indiana, says Vass鈥檚 biochemical methods are 鈥渁n excellent sounding board to nail down the time of death鈥�. Insects are good, but once the soft tissue is gone, so are the bugs, and then, he says, 鈥渨e鈥檙e lucky to get TSD to plus or minus three weeks鈥� 鈥� insufficient precision for a court.

Last August, Haskell sent Vass a cup of dirt that he had collected from beneath the badly decomposed body of a woman found in field near Philadelphia. There was some dried skin, explains Haskell, but no fluids or bugs. He was only able to say that two maggot-growing seasons had come and gone and so the body was about a year and half old. But Vass鈥檚 fatty acid profile pinned it down to within four days.

Still Vass is not satisfied. He wants to expand his forensic tool kit to give a more precise TSD for fresh corpses, like those of four women found strangled in a wooded area in Knoxville in 1993. A local man was accused but the charge didn鈥檛 stick. Vass used fatty acids in the soil to give the police a TSD within a range of a few days, but the man had alibis for each of those days. 鈥淲e needed hours, not days,鈥� says Vass. The case remains open.

In the future, Vass may be able to solve similar cases by looking for TSD markers inside the body. Although soil analysis can be done with fresh corpses, it can鈥檛 narrow TSD to hours because of the lag time between decomposition and the draining of fluids into the soil. Vass鈥檚 team is searching for proteins and other molecules that start to break down and accumulate in cadaver tissue within hours of death.

Synstelien鈥檚 autopsy today is part of that study. Undeterred by her failure to find an intact heart in the body, she shifts her attention to the abdomen. To her delight, the liver is still in decent shape. She snips a piece, drops it in a vial, and moves on to the legs. Amidst throngs of gorging maggots she cuts into the thigh and collects a stringy inch of muscle.

So far, the group has discovered a few promising indicators in the heart, liver, kidney and muscle. As organs liquefy, says Synstelien, there is a steady increase in certain amino acids, the by-products of protein decay, as well as putrescine and cadaverine, molecules resulting from the breakdown of the amino acids lysine and ornithine. Vass鈥檚 team is also tracking the transformation of a brain chemical called glutamate into gamma-hydroxybutyrate, or GHB 鈥� the compound also found in a 鈥渄ate-rape鈥� drug. This technique is accurate when organs and deep muscle tissue are still on the body. After that, Vass must switch to the soil.

To maintain the Body Farm鈥檚 authenticity, there are no restrictions on insect and carnivore activity there. Large iridescent blowflies deposit eggs freely in any available orifice; beetles and spiders ravage skeletons from skull to metatarsal; vultures, possums, rats and raccoons make a meal of defenceless limbs. Vass points out a handful of sites where he buried bodies in preparation for a training visit by FBI agents, to take place later this year. Agents will try to locate the corpses with ground-penetrating radar 鈥� an antiquated technique, according to Vass, who wants to develop better ways for locating bodies (see 鈥淪hallow graves鈥�). 鈥淲hen they鈥檙e found it鈥檚 usually accidental, like a dog comes back with a hand in its mouth.鈥�

To improve on the current technology, Vass wants to couple radar with sonar to make a device capable of penetrating deeper into the ground while giving a clear picture of what鈥檚 there. The combination of waves, he explains, will pick out the unique vibrations of human bones.

Vass and former graduate student Jennifer Love have already trained an electronic nose that can detect airborne vapours emitted by corpses in shallow graves and on the ground (麻豆传媒, 17 June 2000, p 21). The next step is to identify individual chemicals within those vapours, as well as figuring out which chemicals are used by police dogs to sniff out missing bodies, so that e-noses can do the job.

We head back to the tool shed, where the newest arrivals are laid out in the midday sun. The smell of death has attracted swarms of ravenous blowflies, which descend en masse on the ripening feast. People tend to leave their remains to the Body Farm because they鈥檇 rather decompose naturally then be pumped full of chemicals. 鈥淪o many people are interested, I can鈥檛 keep up with the paperwork,鈥� says Synstelien. Local morgues also donate unclaimed bodies, and families who can鈥檛 afford a burial often bring relatives here.

By now I am unfazed by the gruesome sights. But I doubt I鈥檒l be signing up for the Body Farm as my final resting-place. Nor, for that matter, will Vass. 鈥淚鈥檓 not feeding the insects,鈥� he says. 鈥淣o way.鈥�