Why police should use new crime scene mapping technology
A picture may be worth a thousand words, but crime scene mapping using 3-D laser scanners provides context, accuracy and speed
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By Joe LeFevre
In crime scene work, good photos are necessary to tell the visual story of what took place. Photos may lack context, however, making a diagram necessary. Rooms with alcoves, made in odd geometric shapes or just plain not square don't always display well with pictures alone.
Mapping a crime scene factually takes time. It can be the most time-consuming and tedious part of some investigations. But creating an accurate diagram helps to preserve the location of evidence and aids in putting it into context. Diagrams convey scale and distance in a way that photos often cannot capture.
Historically, mapping was done through measurements taken via tape measures. Steel and fiberglass measuring tapes are the workhorses for collecting measurements. For larger, outdoor scenes a walking wheel might be added.
Technology has decreased the time it takes to map a scene, and some newer technologies promise to help further reduce the time needed. More importantly with the newer technologies, the time reduction does not come at the cost of accuracy.
3-D laser scanning
One of the newer technologies for mapping crime scenes is the 3-D laser scanner. The original technology was developed in the 1960s. By the mid-1990s advances in technology allowed scanners to become portable. In the last 15 years the cost of a scanner has decreased, and police agencies can now reasonably afford one.
A 3-D scanner is like mating a total station (surveying instrument) to a digital camera and pumping it full of steroids. Unlike the total station, a 3-D scanner does not need targets. The laser can reflect off the majority of surfaces to produce measurements on everything within its line of sight.
The laser takes a measurement, moves a millimeter and then records the next measurement. It repeats this, measuring out tens of thousands of points every second. After about six minutes a scan is completed, and the device can be set up for the next scan. The device also has the ability to record digital photos of the scene.
Due to line-of-sight issues, it might take multiple scans to fully cover a room. However, the time to move a 3-D scanner is quick compared to a total station.
Once the data is downloaded, all the separate scans can be stitched together to create a 3-D model of the crime scene. Each dot measured becomes a point known as a point-cloud. All the points in the point-cloud are overlaid with color from digital photos, converting them into a photorealistic 3-D environment.
The crime scene model is almost like the environments in first-person video games like “Call of Duty.” It is not an animation or a simulation. It is a faithful and accurate recreation of the scene. Unlike an animation, this rendering is not based on opinion. It is a purely fact-based recreation of what was at the scene.
Having a photorealistic model of the crime scene allows anyone to walk around a pristine version of the event. It is not a computer drawing of the scene with cartoon symbols representing evidence. It is scale simulations of the real walls and the actual evidence from the scene.
Using a photorealistic model to conduct a walk-through of a scene can be powerful. Imagine after an officer-involved shooting being able to virtually allow investigators to stand in the spot where an officer stood to see his or her view of the suspect. Picture the power of walking a jury around a scene versus presenting them with overhead sketches and still photos.
Court case scenario
I assisted on a case that was the first time a 3-D scanner crime scene model display was used in a Wisconsin court. In this case, a woman was found dead in her bed with a gunshot wound to her temple. A second bullet hole was on the wall just to the left of her.
Scanning the room of the shooting took less than 30 minutes. We conducted four scans with our 3-D scanner. Each scan took six minutes, and it took less than a minute to move the scanner from spot to spot. Additional work was done after the scanning, but the scanner and operator were out of the scene quickly to allow other investigators space to do their jobs.
The victim’s husband was the suspect, and it took a day to locate him at an address out of state. There were a few variations to his story, but all of them involved a malfunction with his firearm leading to an unwanted discharge. Tracking back the possible trajectories for the two rounds did not line up. Some lateral movement took place.
A two-dimensional overhead sketch of the scene did not show the scene as accurately as the 3-D model. As I testified, the jury did not look confused. Moving about the virtual scene illustrating details, I could see comprehension in their facial expressions.
To this day we don’t know why he fired two shots. Our best theory was that his first shot missed and thus he moved to fire the second shot. The jury seemed to agree. They found him guilty of first-degree intentional homicide after only a couple of hours deliberating.
The defense had used a strategy of trying to confuse the jury. They put multiple experts on the stand to talk about firearm malfunctions and ballistics. These technical confusion tactics did nothing to undermine the virtual environment we created.
Affordable and accurate
Crime scene 3-D scanners are getting into a price range more departments can afford. A proficient operator can have a scene scanned faster than traditional tape measure mapping techniques. This means that for some agencies, this technology can have a cost savings effect over time.
The technology can also improve investigations and better serve citizens. Longer times at a crime scene create more issues. At an outdoor scene, it leaves investigators exposed to the elements and allows onlookers an easy view of the scene. At vehicle crashes it causes roadways to be closed longer, creating a risk of other crashes due to traffic backups. For indoor scenes, it requires businesses to be closed or residents restricted access from their homes.
Modern 3-D scanners enable faster times on scene, as well as a high degree of accuracy. The 3-D scanners record more points of measurement than other traditional measurement techniques and provide a photo-realistic virtual environment that can be invaluable during the investigation and in the courtroom.