Why Give a Dead Man a Body Scan?

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.