Popular Science: May 2007 Archives

It's arson, bomb, and booby trap week at one of the nation's toughest forensics academies.

Copyright Jessica Snyder Sachs, as first published in Popular Science

All photos courtesy NFA.

A morning mist clings to the foothills as 15 crime scene investigators from across the country approach a shrapnel-pierced Pontiac Bonneville outside Knoxville, Tennessee. Minutes before, a fiery blast engulfed the car's passenger area, exploding the side windows and sending the crazed-glass windshield arcing, slo-mo, 50 feet through the air.


Scene commander Tom Sparks, a beefy lieutenant with the Hartselle, Alabama, police department, designates a sketch artist and photographer to record the vehicle exactly as found and assigns five more CSIs the task of dismantling it for evidence regarding the cause of the blast. Another seven line up with Sparks along one side of the scene perimeter. "Step," he bellows. They move one stride forward before bending to mark potential clues. "Step!" Within minutes, the sodden ground blossoms with orange evidence flags.

Back at the Bonneville, Joy Smith, a tall, blonde evidence specialist from Modesto, California, peers into the red-clay hole where the passenger seat and floorboard had been. She searches for anything remotely bomb-like in the surrounding jumble of shredded wiring, metal and plastic. "Now I see the wisdom of spending time at Radio Shack," she says. "It all looks like car parts to me."

Thirty minutes into the investigation, crucial clues emerge. From inside the passenger door a team member pulls a chunk of galvanized steel with threads on one side and the raised imprint "1 1/4" on the other. "Looks like we've got a 1 1/4-inch pipe," he says. Others pull matching bits of steel shrapnel from the perforated headliner. A cobalt-blue sheen marks the shorn edges of several pieces-the signature of a high-power explosive.

From the shredded driver's seat, Ohio crime technician Matt Dulaney digs out a curl of flattened metal and holds it to his nose. "Gunpowder," he says. "Doesn't a windup clock have a round spring?" The perimeter searchers, for their part, have found shreds of duct tape that, all agree, could have held a pipe bomb and detonator together. The CSIs confront a grizzled former Marine turned explosive ordnance expert. "Very good," he says, nodding. "I put a pound of C4 in the pipe, used a clock timer, and shoved it all under the passenger-side seat."

Time to move on: Knoxville bomb-squad commander Van J. Bubel has other surprises in store this morning. He directs the group's attention to a shoe bomb laced to the elegantly turned foot of a fashion mannequin standing across the field.

"She's just like that guy on the airplane," says Bubel, a detonator cord in hand, "only smarter."


So goes a typical day in Week 7-arson, bombs and booby traps-at the National Forensic Academy, a joint project of the National Institute of Justice, the University of Tennessee, Oak Ridge National Labs and a host of state and local law enforcement agencies. The 10-week course includes units on postmortem fingerprinting, blood spatter, skeletal scatter, grave detection, cybercrime and weapons of mass destruction, and wraps with students resolving a gauntlet of mock crime scenes under the demanding eye of an FBI evidence recovery team.


Now in its second year, the National Forensic Academy aims to establish high national investigative standards for a field that sorely lacks them. The truth is, unlike the highly specialized lab scientists on TV's CSI, most U.S. crime scene investigators come from the rank and file of local police departments and sheriffs' offices. Their training varies as widely as the budgets of their municipalities. The result: Countless cases get dropped when lack of expertise results in missed clues and spoiled evidence; other cases get shredded in court a la O.J. Simpson, when defense attorneys attack less-than-perfect crime-scene procedures.

Not that the academy's cadets are greenhorns. Virtually all the men and women in this, the school's fifth session, have already attended a half-dozen or more courses in evidence collection and served years on the CSI beat. Modesto evidence specialist Smith, to name one, arrived with more than 450 hours of training and eight years of field experience under her belt. "But you can't compare sitting in a classroom listening to someone lecture out of a book to coming here and getting hands-on training from the best people in every field," she says.

Indeed, the academy has already earned an international reputation for the sharp realism of its training exercises and the unprecedented caliber of its faculty. One has only to consider the macabre list of school supplies: Each class works with a half-dozen human cadavers, two sets of skeletal remains and several pints of fresh blood. Academy coordinators Jarrett Hallcox and Nathan Lefebvre also scrounge up two cars and a couple of condemned houses for each class to blood-spatter, burn, and bomb.

The academy's hallmark style of extreme authenticity stems in large part from the University of Tennessee's world-renowned forensic anthropology department. Its outdoor anthropological research station-widely known as the Body Farm-is the only place where exercises in grave detection and body recovery involve actual (donated) human remains.

The value of working with "the real stuff" can't be overstated, says Hallcox. "Some of these investigators come from areas where body exhumations are once-in-a-lifetime events. But after our training, they'll be able to meet the challenge with genuine experience." There are limits, Hallcox admits.

"We didn't use a real body for the shoe bomb," he explains apologetically during bomb week, "because Nathan and I would have gotten stuck with the cleanup." Students also spend three days at the state medical examiner's office in Nashville, where they learn to fingerprint cadavers (a chunk of Silly Putty helps roll prints off decomposing fingers) along with trickier techniques such as lifting prints off thighs and buttocks. The latter can prove crucial to cracking homicides that include rape or physical struggle. But no students in the class had ever mastered the skill before Week 4, when Art Bohanan-inventor of the portable "superglue" fuming technology featured on CSI-taught them to warm the body part to around 70?F, fume it with cyanoacrylate (heated superglue), dust it with magnetic powder, and lift the clearly visible print with contact paper.

The academy's world-class faculty also includes renowned forensic anthropologist and Body Farm founder William Bass, who in Week 5 taught the class how to extract fingerprints from the sloughed off "glove" of skin sometimes found next to a decomposed cadaver. (Soak the tissue overnight in a bucket of water, and slip your own hand inside the stocking-like glove.) Paulette Sutton, the widely published protegee of Herbert MacDonnell (the father of bloodstain-pattern analysis in North America), runs blood-spatter week; and forensic biochemist and time-of-death expert Arpad Vass of Oak Ridge National Labs does triple duty with bloodborne pathogens (Week 1), human decomposition (Week 5) and weapons of mass destruction (Week 9).

Day two of burn and bomb week finds the National Forensic Academy's forensic anthropologist Joanne Devlin striding away from a kerosene-doused Chevy Citation she just torched. A burned-bone expert, Devlin teaches fire-fatality and arson investigation, with special emphasis on the recognition and recovery of charred skeletal remains. Her expertise lies in the interpretation of the burn-altered signs of bullet wounds and other trauma. She has also become the academy's designated arsonist, having spent the previous weekend burning down a four-room farmhouse for a Wednesday field practicum.

Today Devlin and her co-instructors intend to teach these CSIs to make preliminary, on-the-scene determinations concerning the possibility of arson-whether for profit (insurance scam), for revenge or to cover up murder. Such quick determinations often prove crucial, because getting results from a crime lab can take weeks to months, and clues missed at the start may be washed away or demolished in the interim.

Already, the class has watched Devlin, veteran fire investigator Mike Dalton and special agent Dennis Kennamer of the Bureau of Alcohol, Tobacco, Firearms and Explosives burn two furnished "burn cells" (mock rooms with one wall left open for viewing) to illustrate the aftermath of accelerant-fueled arson and the results of a lighted wastepaper basket strategically placed in the corner of a room.

The most obvious clues of criminal intent include gasoline trails or "splash and dash" burn marks on carpeting, furniture and walls. Window glass provides other clues: Long shards directly inside the windowsill point to a prior break-in, while small chunks of crazed glass suggest a heat-related shattering.

Where did the fire start? Look up: "Lightbulbs have the obliging tendency to bubble and extend toward intense heat, as if to say, 'Look here, dummy,'" explains Dalton.

Earlier the same morning, the class looked without a flinch at Devlin's PowerPoint presentation from hell. The close-up photographs featured one fire fatality after another, each graphically illustrating the telltale signs that distinguish victims who perish during a fire from those already dead when the fire began-the latter being a red flag for possible homicide.

A mask of soot around the nose and mouth, for instance, paints the picture of a fire victim still gasping for breath when engulfed. A face-down position suggests an attempt to crawl to safety or huddle from overhead smoke. A face-up victim raises more questions. On the other hand, Devlin warns her students against mistaking the drawn-up "pugilistic pose" of a severely burned corpse as a sign of struggle or self-defense. In fact, the pose results from the contraction of cooked muscle.

After a break to let the torched Chevy cool, Devlin herds students to the smoldering vehicle and cajoles them to reach into the char to gauge the fragility of the cremated remains. The student investigators have more difficulty with Devlin's mock human victims-three animal carcasses were burned in this car-than with the half-dozen cadavers they handled in previous weeks at the state morgue and Body Farm. They hang back. So Devlin pushes open the trunk and picks up a molar from the blackened remains of a raccoon. "What if this is the tooth you need to make a positive ID?" she asks, pinching it to dust between her thumb and forefinger. "Oops."

As students begin handling the charred bones, Devlin points out that though the hands, feet and facial characteristics have burned away, the underside is intact: There is not so much as a singed hair where the body rested against the trunk floor.

Devlin also wants her CSIs to experience the difficulty of distinguishing charred bones from other fire debris. Among her class exhibits she includes a dark version of "Where's Waldo?"-a trough of charred skeletal remains mixed with look-alike fire debris such as burned and crumbled ceiling tiles.

The previous weeks of fieldwork have already sharpened the students' powers of observation in ways they had not imagined possible. During a Week 5 daylong exercise in "surface scatter," the class divides into two teams, each assigned to recover a separate set of 30 skeletal fragments in different sections of the Body Farm. Instructors planted the weathered bones in the wooded enclave's thick underbrush, just as wild animals might scatter the remains of a homicide victim. "The bones looked just like sticks and chunks of wood," says Baton Rouge crime tech Pammy Anderson. Nonetheless, Anderson's team found all but one of its scatter set while the other team found every bone plus an ulna (forearm) left by the previous class. It's a matter of utmost pride: The score of the two teams combined surpassed that of any previous session.

By Thursday night, the academy's fifth class is ready for some mindless entertainment, having doffed class uniforms (black boots, combat pants, and polo shirts emblazoned with a skull, gun and fingerprint) for jeans and sweats. By 9 p.m., most of the crew has settled, beer and pizza in hand, in front of the TV at one of the corporate apartments that serve as the school's upscale dorms. It's time for America's favorite prime-time drama, a show that some in the room love and some hate but all agree features a lot of "in your dreams" stuff: CSI. The show has also heightened the public's expectations of what CSIs can do and how fast they can do it.

For starters, several rush to point out, CSI's college-educated, city-roaming cast of characters would, in real life, belong to the ranks of don't-get-your-hands-dirty "lab rats" who work within the confines of state and regional crime laboratories. Some of these labs do, in fact, field mobile units to assist local police with the occasional scene investigation, "but most of the time, we're on our own," says Tim Horne, an investigator with the Orange County, North Carolina, sheriff's office. "We collect it, and 90 percent of the time, we process it ourselves." And in a typical, medium-size law-enforcement agency such as Horne's, in-house processing means whatever the local investigators can pull off in the ad hoc evidence room.

As for the technology employed on CSI, this audience agrees that, for the most part, it's real, even if pricey, exaggerated and needlessly flashy. Hooting begins as they watch an audiovisual expert in the fictional Las Vegas crime lab zoom in for a close-up of a mole on the neck of an out-of-focus figure in a confiscated snuff film. As every investigator learns when dealing with security camera videos, you can't focus an already out-of-focus picture. (Digital sharpening can produce an image that looks more focused but at the cost of detail and accuracy.) Nor, investigators point out, can you get blood to fluoresce in broad daylight, something the fictional Warrick accomplishes after the next commercial break.

But the biggest beef this class has with Hollywood's glitzed-up version of their work is the speed with which the prime-time CSIs get their results. "They scan in a fingerprint and presto, up comes the name of a convicted felon," scoffs Houston crime technician Christopher Duncan. "I wish!" In reality, fingerprint matching takes days to weeks using AFIS, or Automated Fingerprint Identification Systems, the computer database that searches for matches against the prints of persons arrested in a given state or region. Even then, the computer database spits out not one but an array of close matches, leaving it to the investigator to make the painstaking side-by-side print comparisons.

As for getting a match for a DNA sample lifted from a crime scene, try months to over a year, depending on the backlog of cases being run through such state and national databases as CODIS, or Combined DNA Index System. "All you can do is submit your evidence and take a number," says Horne. "Our case may be important, but so are those of every other agency in the state."

All agree that the show has wildly distorted crime victims' expectations as to what investigators can or will do. "One lady demanded to know why I wasn't swabbing her windowsill for DNA," relates Mississippi detective Craig Burdett. "Even if I could get a sample, we're not going to run a $500 DNA test over a $50 stolen TV."

Whether they come from rural sheriffs' offices or big-city police departments, every one of these crime scene investigators knows the frustration of begging for funds to pay for outsourced tests such as DNA fingerprinting, as well as the basic chemicals and equipment needed for evidence processing. "Just because we know how to do it doesn't mean we'll get the materials," explains Horne. "So while we appreciate all the cutting-edge stuff we've been learning, the best is when they give us the Wal-Mart version."

Which explains why the class's hands-down favorite technique is an on-the-scene print-lifting method learned in Week 3. It employs superglue and cigarette ashes in a jerry-rigged print-fuming chamber made from a Styrofoam cup. They also enthuse over recipes for fingerprint-lifting gels and strips cooked up using dollar-store items like glue sticks, glass cleaner and a dozen-odd types of duct, masking and adhesive tapes. "Our department's a lot more likely to let us buy a $3 stick of Elmer's blue glue than a $25 bag of chemicals," Horne says.

Eager to apply their new tricks, the students mull the convictions that might have been: "For years, I've been trying to get prints off the cheap sandwich bags our druggies stuff with marijuana and crack," says crime technician Steve Smith of Montgomery, Alabama. (Apparently, higher-grade Ziploc bags give up their secrets more easily.) But now Smith knows a correspondingly cheap trick that will bring out prints on the flimsiest of plastic. Using an ordinary aquarium as a fuming chamber, he will heat a few drops of superglue to create a cloud of whitish fumes that adhere to the print's amino acids. He'll then gently stretch his evidence across an embroidery hoop and spray the print (faint white from the superglue) with a fluorescing dye so that it pops up bright orange for a photograph clear enough to run through the AFIS database. Others brood over the killers they might have put behind bars had they known then what they know now. Tim Carnahan of Burlington, Kentucky, describes a case in which a young woman was bludgeoned to death in her garage after a wild chase that started at the front door and wound throughout the house. "We had a good idea who did it," says Carnahan. "But we didn't know how to read the blood spatter to determine the weapon, or even the number of attackers. Next time will be different," he vows. (A suspect has since emerged and Carnahan plans to revisit the blood-spatter evidence.)

Already, alumni of the academy's inaugural year, 2001, have begun to make their mark. Back in Cocke County, Tennessee, detective Derrick Woods prepares for grand jury testimony with full confidence that he has a murder conviction all but in the bag. "I told the guy flat out that it couldn't have happened that way," he says of a shooting to which he responded a week after graduating from the academy in the summer of 2002. When Woods arrived on the scene-a disheveled mobile home-he found a corpse crumpled in front of a couch and a suspect. "The individual told me he'd pointed the gun at the victim just to scare him," Woods recalls. "He claimed that the victim jumped up and grabbed the gun," which went off accidentally during the ensuing struggle.

The shot was at close proximity all right, says Woods. "But there was no blood above the couch. It was on the side wall, and when I looked closely I saw that both the direction and depth of the spatter pointed down." Woods says his academy training told him that the victim had to have been shot at an angle from above. "When I confronted the individual with what I saw, he admitted I was correct."

For session four graduate Bobby Moore, a Lynchburg, Virginia, investigator, the puzzle pieces began falling together even before he left Knoxville. Moore describes a shooting that occurred 6 months before he left for the academy. Police found the victim, a middle-aged woman, shot in the head and sitting upright on the floor in a room barely heated by a wood-burning stove. Crime-lab tests on the gloves she wore came back positive for gunpowder residue, suggesting she'd been handling a gun, though no gun was found at the scene. Even more confusing, bleeding from her massive head wound had produced a strange pattern of staining: strips of blood-soaked clothing alternating with completely blood-free fabric.

"It was one of those cases that just didn't add up," Moore says. "When I came to the academy, I left behind a lot of uncertainty as to what happened and exactly where this woman had been when she was killed." By the time Moore got back, he says, "I could see the whole scene play out in front of me." Moore applied his new understanding of gunshot residue and bloodstain pattern analysis to reconstruct how the victim, shot from the front at close range, had tumbled forward onto the wood-chip-littered floor, then raised her gloved hands to her face, smearing them with gunshot residue from her skin. Blood pouring from the wound soaked through her clothes, except where folds of fabric had crumpled together when she fell. Consistent with this scenario were the splinters and wood chips Moore had noticed in the victim's hair-a sign that at some point she had been on the unswept floor. "What I found really interesting," says Moore, "is that someone had then lifted her up off the floor to look at her." And in so doing, had unfolded the pleats of clothing that had remained clean. "Only someone who cared about the victim would have done that."

On his return from the academy, Moore went to the prosecutors who were considering pressing charges against the dead woman's boyfriend. "I could explain a lot of things to them," he says, "and we were able to line up all our evidence in a row." Faced with the overwhelming case against him, the boyfriend pleaded guilty to second-degree murder.

Such stories validate the academy's mission of raising the caliber of crime scene investigation in this country through effective training. Already, 66 graduates have returned to their communities not only to use what they have learned but to disseminate it to colleagues. Still, with classes kept small to maximize hands-on training, there's little hope of teaching even a single representative from each of the nation's approximately 18,000 local law enforcement agencies.

"We see ourselves as a model," says Hallcox, "and a possible avenue for setting national training standards in many aspects of crime scene investigation." The Department of Justice appears to agree, if its award of an additional $1 million in hard-won federal funding is any indicator. The money will subsidize police departments and sheriffs' offices that can't afford the $6,500 tuition, and provide seed money for the first research grants awarded by the academy's umbrella group, the National Forensic Science Institute at the University of Tennessee.

Not that real-life crime investigation will ever resemble the seductive wizardry that has turned blood-spatter analysis into prime-time entertainment. "In real life, it's down-on-your-hands-and-knees dirty business," says Anderson. "Ninety percent of the time, what we do is tedious," she adds. "But that other 10 percent makes it all worthwhile."

Contributing editor Jessica Snyder Sachs is the author of Good Germs, Bad Germs: Health and Survival in a Bacterial World (Hill&Wang/FSG) and Corpse: Nature, Forensics, and the Struggle to Pinpoint Time of Death (Perseus).

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Forensic scientists in Switzerland are pioneering a whole new way to do autopsies. No scalpel required.


Copyright Jessica Snyder Sachs, as first published in POPULAR SCIENCE magazine


A light shines under the closed door of a radiology suite, down a darkened hallway deep inside the University Medical Center in Bern, Switzerland. Outside the building, under the glow of a fluorescent street lamp, an empty hearse waits in the loading dock. Tonight the local undertaker is earning some extra money making a special delivery. Entering the radiology room through a back door, he gently deposits a body-double-wrapped inside a blue bag-on the sliding bed of a full-body scanner. The bag, through which x-rays can easily pass, will remain closed while the body is scanned, both to respect the privacy of the dead and so as not to disturb any nonforensic personnel in the room.


Without the bag, the university's Institute of Diagnostic Radiology would not have approved the use of its aseptically clean research facilities for postmortem studies, says forensic pathologist Michael Thali. The Swiss emphasis on orderliness and precision extends to the task of death investigation.


This cultural passion-some would say obsession-for precision becomes clear to any visitor arriving by train here in Switzerland's 800-year-old, meticulously preserved capital. Rows of clocks line the train station corridor, all perfectly synchronized down to the sweep of their prominent second hands. In this spirit, Thali and his colleagues at Bern's Institute of Forensic Medicine are perfecting the ultimate no-mess autopsy: precise, objective and nondestructive, with death's every data point captured permanently on compact discs that the scientists store in the vault of a nearby Swiss bank (where else?).


Thali calls the technique "virtopsy," or virtual autopsy. Specifically, his research team has adapted the twin medical- imaging technologies of computed tomography (CT) and magnetic resonance imaging (MRI) to create three-dimensional, high-resolution computer images of a crime victim's internal organs. Thali pours these digitized blood and guts into a hollow-man replica of the victim. The result is a head-to-toe cybercorpse that a pathologist can view-wounds and all-from any depth and angle, including inside out.


Besides being a bloodless approach to an otherwise messy job, the digitally preserved bodies of the Virtopsy Project have the added benefit of permanency. "Murder victims have the unfortunate habit of decomposing," Thali notes. Of course, police and pathologists have long documented such disappearing evidence with photographs and detailed medical reports. Photos, however, are limited by their two-dimensionality and the inherent distortion of camera angles. And medical reports, according to Thali, remain unacceptably subjective.



It's a criticism supported by the cacophony of the courtroom, where prosecutors and defense lawyers often present dueling pathologists, each reinterpreting autopsy reports to favor one side or the other. Complicating a jury's difficulty in following such arguments are the typically gore-drenched autopsy photos that prompt many to turn away in horror. "We [in Switzerland] are not so used to shows like CSI," Thali points out. "It can be a real problem."


In the future that Thali envisions, any pathologist taking the witness stand can bloodlessly redissect the victim in full view of the jury by calling forth the original data stored on the discs. "Graphic, yes. Gory, no," he says.


Over the past three years, Thali has performed more than 100 virtual autopsies, each followed by a traditional autopsy to confirm his findings. Although his experimental technique has proved highly accurate, he expects to complete at least 100 more cases before the first virtopsy debuts in a court of law.


"Virtopsy is still like a little baby," Thali says. "It is not yet ready to stand alone." First he must show that it is at least as accurate as traditional autopsy. So far, he says, virtopsy has been particularly good for detecting the internal bleeding, bullet paths and hidden fractures that can be maddeningly difficult to

isolate amid the mass of blood and gore that results when a pathologist is forced to essentially eviscerate the body.


Best of all, perhaps, is the way CT and MRI scans highlight emboli-air bubbles that obstruct blood vessels and that have most likely entered the body through a wound of some sort. Such effervescent evidence can vanish as soon as a pathologist slices open a vein or organ to look for it, Thali explains. "So difficult is this problem that some have proposed performing underwater autopsies in swimming pools to detect escaping air bubbles," he says.

The scans also make it much easier to detect aspirated, or inhaled, water and blood in the lungs. These forensic "vital signs" tell a pathologist that a victim was alive when he entered the water or sustained an injury, which can be crucial for determining whether an apparent drowning or car crash was staged to cover up a murder. Pockets of air, blood or water show up clearly on CT and MRI scans as spots-black, bright white or gray-against the background of body tissues.


On the negative side, virtopsy remains woefully inadequate for diagnosing poisoning, as well as common natural causes of death such as infection or heart failure. "Obviously," Thali admits, "it's very important to be able to rule out such natural causes in a case of suspected murder."

The forensic question before Thali tonight is whether or not the elderly woman inside the body bag was dead before she ended up under the chassis of a Volvo sports sedan the previous afternoon. The Volvo's driver insists that he checked his rearview mirror before backing into the parking stall where the body was found. Given the woman's age-70ish-the possibility of a prior heart attack or stroke seems plausible.


Thali's research team began their examination of the body earlier in the day, as it lay face-up on the stone examining table in the forensic institute's second-floor autopsy bay. Visualization specialist Ursula Buck and pathology resident Emin Aghayev prepared the body by affixing buttonlike reference markers across its surface and photographing it with a digital camera from nine angles. Using an overhead light and transparency, they then projected a numbered grid of black points across the body before initiating a computer-guided 3-D scan using cameras mounted on an overhead beam. Turning the body over, Buck and Aghayev repeated the procedure before placing the corpse in a bag and sending it, by private hearse, to the university's Institute of Neuroradiology, several blocks away, for its MRI scan.


Magnetic resonance imaging has become fairly routine in medical diagnostics since its introduction in 1980. Using radio waves beamed through a powerful magnetic field, MRI produces 3-D internal images of unsurpassed detail. But the process remains far from automated, requiring operators to learn elaborate protocols to extract images from different types of body tissue. Complicating matters for the virtopsy project, MRI technologist Karin Zwygart has had to create special protocols to compensate for the lower body temperatures of Thali's refrigerated research subjects. The cooler temperatures would otherwise wreak havoc on results, because the MRI machine operates by translating the signature vibrations emanating from the nuclei of different kinds of atoms. At cooler temperatures, these nuclear vibrations slow down.


On the plus side, the resulting images are of such clarity that they draw amazed inquiries from radiologists whenever Thali displays them at international conferences. "Not only do they not fidget," he says of the corpses, "there is no beating heart, no circulating blood, no digestive motions to blur our images."The body's final appointment of the night brings it to the University of Bern's Institute of Diagnostic Radiology. Here it passes through the doughnut-shaped hole of a CT scanner, which constructs 3-D images of the body from a series of x-ray slices. In the radiology suite's darkened computer room, Peter Vock, director of the imaging institute, shares a computer with neuroradiologist Luca Remonda. As intent as schoolboys with a new videogame, the two men take turns clicking and dragging screen controls to manipulate the image on the monitor. Vock defines and deletes the CT scanner's bed to leave the woman's body suspended in midscreen. Slowly he melts away silvery layers of skin, muscle and connective tissue to reveal a bare white skeleton. He rotates the image, head over heels, pausing to note multiple rib fractures, a broken sternum, a shattered collarbone and crushed vertebrae. Then, layer by layer, he reassembles the body. When he reaches the level of fascia-midway between bare bones and full muscle-he stops again, intrigued by the abnormally high position of the woman's stomach and the telltale indentation, like an overly tightened belt, around the organ's midsection.


"We call this a collar sign," Vock explains. "We think that perhaps the woman's stomach was pushed up through a break in her diaphragm," the large muscle that separates the lungs from the abdominal organs. To get a better look, Vock finishes reconstructing the torso and then slices down through its midsection, five millimeters at a click, until he discovers a dark gap in the white muscle of the diaphragm.


Vock turns the controls over to Remonda, and Thali asks the radiologist to look for signs of inhaled blood in the woman's lungs. Earlier, during the MRI scan, Thali noted light areas in the woman's muscle tissues. If this represented active bleeding, it would suggest that she was alive when the car crushed her body against the pavement. But postmortem injuries can produce some internal blood seepage. More telling would be a clear indication of aspirated blood-a confirmation that the woman was still breathing when she sustained the injuries.


Remonda is on his second or third slice through the lungs when the first white splotches appear. As he continues to click down through the tissues, each bright spot melts away, only to be replaced by others. Clearly, aspirated blood.


Remonda and Vock turn to Thali for his pronouncement as to probable cause of death. "Thorax instability secondary to crushing injuries," he concludes: suffocation following rib fractures so massive that the victim was unable to take a breath.


The next morning Richard Dirnhofer, Thali's boss and the director of the Institute of Forensic Medicine, will perform a conventional autopsy for confirmation. "It will be a bloody mess, to be sure," Thali says with a grimace. "Nobody likes to show that to a jury."At the same time that Dirnhofer is making his first cut, visualization specialist Buck will be hauling her surface-scanning equipment to the police garage where the suspect's Volvo remains impounded. There she will create a 3-D computer image of the car's surface, the same way she photographed the corpse. Buck and Thali will then bring the body and automobile together in cyberspace, matching wounds to car surfaces until they can determine the woman's position as she sustained each of her injuries. Thali is particularly interested in how well the car's rear bumper and trunk lid will match up against the gouges seen in the surface scan of the woman's knees and the deep bleeding the MRI picked up in the muscles over her hips. "This is not some animation program using artificially created models," Thali insists. "You are looking at real data from the original car, the original person, the original wounds and bones." Depending on how the data match up, the driver could face manslaughter charges.

This dynamic matching of wound to weapon is an offshoot of a larger collaboration between Thali's forensic pathology team in Bern and the Scientific Forensic Service of the Zurich police. In 1995 Bern's Dirnhofer called Zurich's chief of forensics, Walter Brschweiler, with a challenge. He wanted a better way to match wounds and suspected weapons than the usual method of laying a photo of one over a photo of the other.

"That is when I thought of Marcel," Brschweiler says. Zurich traffic detective Marcel Braun had been adapting the new technology of photogrammetry for use in accident investigation. Photogrammetry software-originally developed for topographical mapmaking-turns a calibrated series of photographs into a 3-D model. In essence, Braun was using it to rewind multi-vehicle traffic accidents, extrapolating back from the dents and twisted metal of the final pileup to see who hit whom, all the way back to first impact. In collaboration with Thali, Braun adapted the technique to re-create violent deaths from the resulting damage seen on and within the corpses.


One of the most interesting cases on which the Bern and Zurich forensic scientists have collaborated came to trial in July 2003. It was a triple homicide, with three prostitutes found beaten to death in an apartment outside Zurich. Police had

a suspect who admitted to having sex with the women but insisted that they were all alive when he left the apartment.



The murder investigation focused on a deep bite mark gouged into the shoulder of one victim. The man denied biting anyone, and DNA swabs of the wound yielded a mixture of genetic fingerprints that would not stand up in court. The possibility remained that the women had killed each other. Indeed, judging from the size of the bite mark, police originally proposed that the bite on the woman's shoulder came from one of the other two victims. And when the Zurich police obtained dental casts from the other women's mouths, one did fit fairly well with their photographs of the wound.


Meanwhile Thali's team had completed their virtopsy of the three women, with Braun performing the 3-D surface scans. They could now go beyond matching dental casts against two-dimensional photos, to re-create how the teeth penetrated the dead woman's skin.


On a recent morning in his Zurich office, Brschweiler replays the results on his laptop computer-calling up the digitized, silvery-gray replica of the male suspect's teeth and bringing it in contact with the full-color virtopsy scan of the victim's bruised and bloodied shoulder. As the front teeth begin to enter the skin, Brschweiler switches to an underside view. "You see, there is not yet a reaction from the victim," he

narrates, "only the motion of the biter." But as the premolars break through, the teeth begin to drag laterally, widening the wound. "Now see, the woman reacts to the bite. She begins to pull away."


Re-running the simulation again, even slower, Brschweiler underscores the perfect match between teeth and bite marks. He then calls up the digitized dental cast of the dead woman whom police originally linked to the bite. "It matches on the left, but the angle is not the same," he says. "And look here, the small gap between the front teeth is not a perfect match." Importantly, Brschweiler says, the judge and jury were able to follow the re-creations and the science behind them during the suspect's murder trial, which resulted in a conviction.


In their shared pursuit of more-accurate murder re-creations, the Zurich Police Department and the Virtopsy Project have enlisted the additional help of the Swiss army, which has invested a considerable peace dividend in science. Switzerland has the distinction of ranking simultaneously among the world's most peaceful and most militarized nations, having avoided war for more than 150 years while enlisting virtually every male citizen in its military reserves.


"We have the time, people and peace to spend time in research," says Swiss Department of Defense mathematician Beat Kneubuehl, an internationally recognized expert on wound ballistics-the physical dynamics of how bullets, their fragments and their associated air jets pass through the human body. Kneubuehl's interest in gunshot wounds dates back to 1978, when the Swiss army asked him to design a line of ammunition and demonstrate that it met international conventions against unnecessary suffering.

To prove that his bullets would pass through a leg or arm without causing the kind of massive bone and blood-vessel damage that results in amputation, Kneubuehl decided to use simulated body parts instead of cadavers or animal carcasses, partly for ethical reasons. "We Swiss frown on that sort of thing," he says. But the major offense to Kneubuehl's Swiss sensibilities was the imprecision of such targets. "Every cadaver, every human or animal bone is a little bit different from the next one," he explains. "When I want to isolate one variable-the design of my bullet-I must expunge all other variables from my experiments."


Kneubuehl's line of faux body parts fracture, splatter, and shred like the real stuff-just more consistently so. His simulated bone consists of two layers of polyurethane sandwiching an inner layer of gelatin and coated with a thin veneer of rubber. His skulls are melon-shaped spheres with a corked hole for adding gelatinous brain and fake blood. They have been useful for re-

creating fatal beatings and shootings.

On one of Kneubuehl's recent test days, Thali joins him at the Swiss army's wooded training grounds outside the Alpine village of Thun. The sound of machine-gun fire alternates with that of birdsong as the two men enter the smallest of the site's three underground ballistic-test tunnels. Built in the early 1990s to minimize noise disturbance to Thun residents, the 100-, 200- and 500-meter tunnels are the largest underground firing ranges in the world.


Kneubuehl's goals for the day are to study the fleeting expansion of brain tissue caused by the air jet that accompanies a bullet and to measure the velocity of the skull fragments that enter the "victim's" brain. First he uses high-speed stop-action video to capture the expansion of his skull-brain models as each takes a bullet or shotgun load to the head. He then blasts the same ammo through sheets of synthetic bone strapped to big blocks of glycerin soap. Having thoroughly measured the glycerin's consistency, Kneubuehl can mathematically determine the energy of the imploding bone fragments by measuring how far they pass into this test material.


The glycerin soap has the added advantage of preserving the cavity created by the expanding jet of air that accompanies a bullet's passage through soft tissue. Actual brain tissue, in contrast, would immediately collapse on itself. "We know that the dynamic

cavity during the shot is considerably larger than the wound seen on autopsy," Kneubuehl explains.


Thali's mission for the day is simpler: He slips a wig onto one of Kneubuehl's head models for an "execution style" shooting. Thali wants to determine whether it's better to collect gunshot residue from the hair with adhesive tape or to shave the head and go for the scalp.


To the uninitiated, the test shot appears to result in the ultimate "oops" moment, with the brain ending up on the floor as the shattered skull flies against a far wall. "Actually, we see this sometimes in our cases," Thali says. "In Europe, we call it kroenlien, or evisceration of the brain." He retrieves the gunpowder-speckled wig and skull for later analysis and deposits the blob of synthetic brain in a garbage barrel.


As academically interesting, and even entertaining, as these experiments can be, the question remains: How might the Swiss approach to forensics translate in the down-and-dirty world of American murder investigation? Having spent a year working in the U.S., Thali appreciates that few if any American pathologists have the luxury of pursuing experimental methods and exhaustive research studies. "The medical examiner in a city like Baltimore probably sees as many murders in a weekend as I see in a month," he says.



Try closer to a year. The 10 full-time pathologists at Bern's Institute of Forensic Medicine oversee a region of southwestern Switzerland with a population of 1.5 million and perform about 500 autopsies a year, 10 to 20 of which turn out to be homicides. The Maryland Medical Examiner's Office, based in Baltimore, employs a similarly sized staff of 14 full-time pathologists. But the similarity ends there. Overseeing a state with a population of five million, the Baltimore staff performs an average of 4,100 autopsies a year, including 500 to 600 homicides.


Moreover, Switzerland's six institutes of forensic medicine all come under the auspices of the country's well-funded university system. The offices of American medical examiners, on the other hand, derive their funding from budget-strapped city, county and state governments.


The equipment required for a virtual autopsy includes an MRI machine costing upward of $1 million, a CT scanner priced at about $500,000, and 3-D surface-scanning equipment worth more than $100,000. "A lot of medical examiners consider themselves lucky if they have an x-ray machine," says William Rodriguez, deputy chief medical examiner for special investigations at the Armed Forces Institute of Pathology in Washington, D.C. "For the short term, this type of extremely expensive technology will be considered a big luxury."Meanwhile, the need to be prepared to deal with mass casualties has the U.S. Department of Defense extremely interested in setting up virtual-autopsy facilities-despite their high cost-at its massive morgue at Dover Air Force Base in Delaware, Rodriguez says. "As the technology becomes more efficient, this becomes a way to scan many more bodies in a shorter amount of time with fewer pathologists," he explains.


Already Department of Defense medical examiners use a conveyor-belt scanner, similar to those used to screen baggage in airports, to look into soldiers' bodies for bullets, shrapnel and unexploded ordnance. "As the body goes through the machine, we also see skeletal structures and get a pretty good idea of what we have in terms of large injuries," Rodriguez says. "Something more along the lines of what Dr. Thali is doing would allow us to take this down to levels of minute detail."


"Perhaps we in Switzerland have this role to play," says Thali of the opportunity to explore and perfect techniques that might someday transform postmortem exams for the rest of the world. He predicts that virtual autopsy will eventually speed and improve the procedure by guiding the pathologist's scalpel and preserving a record of what the internal tissues looked like before dissection. Still, the word "autopsy" comes from the Greek for "seeing with one's own eyes," and no one believes that virtopsy will ever replace the pathologist's scalpel completely. "What we see with our own eyes," Thali says, "will remain the gold standard in autopsy."

Science Writer Jessica Snyder Sachs is the author of Corpse: Nature, Forensics, and the Struggle to Pinpoint Time of Death (Perseus Books) and, more recently, Good Germs, Bad Germs: Health and Survival in a Bacterial World (FSG).

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