Navigation auf


UZH News

Forensic Medicine

Gantenbein's Shot

With virtually reconstructed crime scenes, suspects, lawyers and judges are instantly transported to the spot where it all took place – and clues to the crime are revealed.
Marita Fuchs
Direct confrontation in court: Being immersed in the virtual crime scene can loosen suspects' tongues. (Illustration by Christoph Fischer)
Franz Gantenbein is a retired office worker from Lucerne, chairman of the gymnastics club, and member of the local adult education center. From time to time he is invited by friends to go hunting. No criminal record, not even a mention of a misdemeanor. Everything would be fine, if it weren’t for the matter with his wife. He has been married to Silvia for 40 years, but what was once a loving relationship has turned into domestic hell. Now, after retirement, things have become unbearable for Franz. His wife despises him. Franz is now 66 and no longer knows how to go on.
One day the neighbors alert the police because the door at the Gantenbeins' is open. The police discover the wife's body lying on the sofa in the living room, hit by a bullet. In front of her on the table is a bottle of gin, lemon slices, an overturned glass. No trace of Franz. Eventually his hunting friends find him on the raised hunting blind in the forest. Franz is arrested.

Franz and his wife are fictitious persons, but a case like this could easily have taken place as described. As it is forbidden for legal reasons to write about proceedings in progress, we are using this case to demonstrate how the police, forensic scientists, the UZH Institute of Forensic Medicine and the Canton of Zurich's public prosecutors today all work together.

To solve crimes, these investigators turn to the latest scientific technologies: Laser scanning at the scene of the crime, computed tomography, magnetic resonance imaging, body surface scanning of the corpse and virtual 3D replicas of the crime scene, all of which which have revolutionized forensic medicine. Unlike what is shown in many crime series on TV, police officers in the Canton of Zurich don't use a camera, tape measure and chalk to record the scene of the crime – they scan the area with laser devices.

Everything is digitally recorded down to the smallest detail. The firearms experts analyze the bullet's trajectory and the shooter's firing position, and DNA traces are captured: Every clue could be important for the later court hearing. One advantage of this approach is that all the data from the crime scene can be re-examined, even after decades. The same applies to the Gantenbeins' living room.

Shooter as avatar

The 3D-Zentrum Zürich – a joint center set up by the UZH Institute of Forensic Medicine (IFM) and the forensic institute of the cantonal and city police – is the next step. Here, forensic scientists, police officers, and coroners bring together information of relevance for the public prosecutors at the hearing. Representing the very heart of criminal investigation, this center at Zurich's Waltersbachstrasse is only accessible to authorized persons with the required security codes.

Lars Ebert, a privatdozent at the University of Zurich and IFM employee, runs the cursor across his computer screen. He is only permitted to discuss pending cases if his interviewer has signed a confidentiality agreement. On the screen, Ebert demonstrates how laser-scanned data taken by the police at the crime scene is used to recreate the room to scale, showing the location of the sofa, the table, and the overturned glasses; even details like electric sockets, a lampshade, the carpet. And the body is also seen lying as it was found.

Anyone not knowing that a crime took place here could be excused for thinking it was an interior in a computer game. It would even be possible to place the shooter in this room as an avatar, a virtual person, says Ebert. He is now working on a project involving the use of a position sensor to calculate and reconstruct the head movements and head positions of people present at a crime scene.

In the middle of the action

It is with the use of a virtual reality (VR) headset that the digitally created interior is made tangible – and the effect is astounding. The scene of the crime becomes vividly real and the user can even walk around in it. Seen from the outside, the person with the VR headset moves across a 5m-by-5m space, holding a pointer in their hand with which they can, for instance, teleport themselves from the virtual door into the living room.

Previously, public prosecutors were provided with documents about the crime scene on a printout or on their screen. "But spatial information can be lost this way," says Ebert. With 3D reconstructions of the crime scene, police and prosecutors see the details in their third dimension. Nowadays, by putting on the VR headset, the public prosecutor can view the scene from the perspective of criminals, victims or witnesses present at the crime without ever having been there. The ability to virtually visit the crime scene also allows experts abroad to make an assessment.

"With this headset, you can jump straight to where it all happened," explains Ebert. In the Gantenbein case, for example, users would see that the shot must have been fired from low down, almost from the ground.

The new technique has been made possible by a tracking technology required for 3D reconstruction. Ebert is a qualified computer scientist who, after a PhD in medical technology, wrote a habilitation thesis entitled The Forensic Holodeck which explores how 3D technology can be used to take the virtual representation of a crime scene to the next level. What particularly matters is that the VR content is adapted to any movement: When movements and images are not synchronized, the VR user will feel sick. "We therefore have to know at every millisecond exactly where the person is," says Ebert.

The other piece of the crime-solving puzzle is added by the IFM at Irchel campus. Here, autopsies are performed on all corpses resulting from deaths that occur suddenly, unexpectedly and under suspicion of violence in the cantons of Zurich, Zug, Schwyz, Lucerne, Obwalden, Nidwalden, Uri and Glarus. Mrs. Gantenbein's body would also be brought to IFM.

Virtual autopsy

Before the body is dissected, it is run through a computed tomography (CT) scanner. At IFM, the rule is: No manual autopsy without a prior CT examination. "Conventional autopsies destroy the body. By contrast, scanning technology is non-invasive," explains Michael Thali, director of IFM and co-founder of virtual autopsy.

Anatomical and morphological findings are clearly visible in the computer images of the body. Certain features, such as air inclusions, can be seen even better than with scalpel autopsies, because the air cannot escape as it can with incisions. In a 3D reconstruction of a body, forensic scientists can also calculate the exact angle of incidence. "Today, 60 to 80 percent of forensically relevant causes of death can be determined using virtual autopsies alone," says Thali. The forensic scientist calls his virtual autopsy method "virtopsy".

Delirious or just tipsy

In addition to CT, magnetic resonance imaging (MRI) is also used, depending on the situation. While CT is good for representing bone injury and air-containing structures, MRI is suitable for injuries to organs such as the heart, brain or liver. In addition, contrast media is injected into the blood vessels, enabling miniscule findings in the cardiovascular system to be detected. However, it is important that the body has not yet started to show any signs of stronger decomposition, as autolytic processes make the blood vessel wall fragile which can lead to a leak of the contrast media.

In the meantime, forensic doctors have developed the use of MR spectroscopy to determine whether the deceased person had alcohol in their blood. "We can establish whether there was a high concentration of alcohol or whether the victim was only tipsy – only slightly intoxicated," explains Dominic Gascho, radiology technologist at IFM.

But the body is not only examined in detail on the inside; the surface of the body is also of interest. A 3D surface scanner is used to record gunshot or bite wounds and external injuries such as kicks or indentations from the impact of a heavy object. All the findings from the skin surface, CT and MR examinations are combined, and the body is displayed on the screen in a three-dimensional reconstruction. The forensic doctors can view the blood vessels or bones, turn them around and locate injuries with a click of the mouse. As Michael Thali explains: "The various imaging methods provide the raw data but we do the evaluating and interpreting work." This is where specialist expertise comes in.

Direct confrontation

Before the court hearing, the public prosecutors make use of the chance to virtually inspect the crime scene using a VR headset giving them a detailed picture. They also have all the forensic information available on the condition of the body. Present at the trial are the defendant, the defendant's lawyer, the public prosecutors, the judge and the forensic doctors. The defendant is asked to put on a VR headset. Direct confrontation, i.e. total immersion in the virtual crime scene, can loosen suspects' tongues. However, if a suspect starts to weave a web of lies, he or she needs to be extremely skilled to catch the scientists and investigators out.

The headset also transports Mr. Gantenbein back to the scene of the crime; he can even walk around his own living room. He describes the course of events. His wife had been drinking and insulting him once again while he was cleaning his gun, he remembers. When she threw the glass at him, he ducked to the floor and fired a shot. It was not intentional. An accident.

This is Gantenbein's version. But according to the forensic scientists' calculations, it couldn't have happened like that: From the virtual autopsy they were able to prove that the wife had been shot but that – due to the detection of a laryngeal fracture – the death was not caused by a gunshot, but by strangulation.

With the help of the UZH Institute of Forensic Medicine, virtual crime scene inspections have been put to use in two real court cases to date. However, says Lars Ebert, although these new means can be used to search for the truth, responsibility for ultimately establishing the truth still lies with the courts.