On the search for clues with a laser scanner after fires and homicides

What exactly happened here? This is the central question after a fire or violent crime. The St. Gallen Cantonal Police use state-of-the-art laser technology from Leica Geosystems, part of Hexagon, for evidence collection. The forensic experts at the Forensic Competence Center must work quickly and precisely to reconstruct events, provide evidence, and evaluate them – essential for proving cases in court.

It smells of burnt wood and melted plastic. Extinguishing water drips from the blackened roof beams to the ground floor. The ceiling has collapsed, and the walls are missing. Debris is everywhere: charred furniture, broken roof tiles, bent metal parts. Everything is sooty, damp, devastated. The fire in this single-family house leaves behind great destruction and many unanswered questions. This is where the police’s forensic crime scene work begins: determining the cause of the fire, documenting crime scenes, and reconstructing events. Or as Sven Gustavsson, an expert in fire and special cases at the St. Gallen Cantonal Police, says: “Freeze the moment and capture all traces.” A job with many challenges and adversities.  

Leica Cyclone REGISTER 360 (BLK Edition) - scan of a fire-damaged building

Forensic Science with State-of-the-Art Technology

“Determining the causes of fires is one of the most difficult fields in forensics,” admits Sven Gustavsson. “Arson can never really be ruled out. Manipulated electrics or deliberately set fires are hardly distinguishable from normal fire events.” Additionally, fire or explosion sites are often dangerous. Unstable building parts and toxic fumes make the work difficult. The forensic team must document the fire site quickly and efficiently. The St. Gallen Cantonal Police use state-of-the-art technology – including the Leica BLK2GO, an advanced, portable, and imaging laser scanner. 

Leica Geosystems BLK2GO used at St. Gallen Police for fire, arson and explosion investigation

However, laser scanners are not only used for fires. Their versatility allows us to use them in various forensic investigations, from documenting crime scenes to creating scaled plans after serious accidents.

In special cases, such as violent crimes, it is also necessary to quickly and visually capture the crime scene with all its details. The St. Gallen Cantonal Police also have a GNSS-RTK rover, a Leica GS18 T, especially for creating scaled plans after serious accidents.

Leica's original tilt compensating GNSS RTK rover

Top Documentation in Minutes

There are well over 300 fire cases annually in the canton of St. Gallen. Most of them are small fires. “Our department is only called in when the property damage is high or arson is suspected, i.e., when an event has criminal aspects,” explains Sven Gustavsson. “In such cases, top documentation is needed that can be used in court.” After all, the special department is called in for about 135 fire cases annually – about every third day. The Leica BLK2GO is always in their luggage. This lightweight and easy-to-use laser scanner allows forensic technicians to create a detailed 3D image of the fire site within minutes. “With the Leica BLK2GO, we simply walk through the building while the device scans fully automatically,” explains Sven Gustavsson. The advantage: Unlike terrestrial scanners, the Leica BLK2GO is carried and, therefore, does not require extensive cleaning after use, as it does not come into contact with the “dirty, sooty, and damp environment.”

Every Detail Can Be Relevan

For the experienced forensic technician, the Leica BLK2GO offers another decisive advantage: “We can capture a location incredibly quickly – usually a few minutes are enough. This is also important because the Institute of Forensic Medicine always wants to examine the deceased as quickly as possible in cases of death to determine the time of death.” Additionally, the device’s high precision captures a situation in detail. An essential point for forensic work, says Sven Gustavsson: “We never know in advance what is relevant at a crime scene. Only in the course of the investigation can an object, for example, prove to be important, perhaps because it is a murder weapon. For this, everything must be precisely documented, which is easiest with laser scanning.”

Always Back at the Crime Scene

The room of the Fire and Special Cases Department resembles a tech lab. “All the technology here is state-of-the-art,” says Sven Gustavsson proudly. Almost 10 monitors stand on the four worktables, between microscopes, headphones, and other technical devices. Various VR glasses are stored on the shelf. The latest model is wired on the floor. “This VR headset is the best product currently available on the market. It is very valuable for our work because you can revisit a scanned room or a fire ruin at any time. You can return to a crime scene or inspect a building that has since been demolished.” The corresponding software makes it possible.

Indispensable for Police Work

The Leica BLK2GO takes millions of precise measurements to recreate the space in 3D. The BLK2GO GrandSLAM technology simplifies the representation of spaces in real time. The data forms the basis for accurate floor plans and 3D visualisations of fire sites and crime scenes. To create and edit the 3D views, the St. Gallen Cantonal Police use the Cyclone REGISTER 360 PLUS software from Leica – a point cloud registration software for 3D laser scanning and a “command centre for reality capture.” Cyclone REGISTER 360 PLUS is available in a special BLK edition optimised for use with the BLK Reality Capture product family.

In homicide cases, ballistic analyses and other investigations complement the 3D documentation. When Sven Gustavsson and his team have completed a case and everything is documented, they send the documents to the internal investigators and the public prosecutor’s office. The 3D visualisations help them find causes for fires, search for traces, and convict perpetrators. “Laser scanning has taken police work a decisive step further – this technology is indispensable today,” says Sven Gustavsson, turning back to the screen to prepare the 3D scan of the latest fire case for his colleagues. The Leica BLK2GO is not just a tool; it’s a game-changer in the field of forensic investigations, significantly enhancing our ability to reconstruct events and provide crucial evidence.

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The Expert: Sven Gustavsson