Three-Dimensional (3D) Scanning in Forensic Investigations
Tuesday, June 5, 2018
by: Nicolaus Faino, MS, CFEI

Section: Secondary Article


Author Bio

Nicolaus Faino of JENSEN HUGHES, is a Mechanical Engineer who specializes in laboratory and field analysis of materials and mechanical systems. He holds an M.S. in Mechanical Engineering from the Colorado School of Mines. Mr. Faino investigates residential and commercial plumbing, piping, and appliance failures related to water loss damage and construction defects. He is also experienced in applying 3D laser scanning techniques for scene preservation, computational stress modeling, and dimensional analysis; and he is an operator of the FARO 3D laser scanner. Mr. Faino provides technical support, litigation support, and expert analyses to law firms, insurance companies, and industry.
When an incident occurs, forensic investigators must document the scene to preserve information in case there is future litigation. Many times, an investigator only has one chance to document the conditions of a scene before it is altered by remediation or clean-up efforts. Additionally, relating complicated engineering concepts to a fact-finder or jury can be difficult without clear and concise visual aids. Three-Dimensional (“3D”) scanning enables investigators to capture a large amount of data in a short period of time and to distill that information into a three-dimensional model that people without technical knowledge can visually understand.

3D models enable a viewer to virtually walk through a scene and observe the conditions that were present when the scene was scanned. A 3D scan is essential for preservation of a scene that will be digitally revisited in the future. Fly-through videos can be created from the 3D scan that show the scanned scene or object from various viewpoints and orientations, and provide perspective that can be lost when viewing 2D photographs. Because it is such a powerful tool for preserving evidence, the public and government sector have already begun to embrace 3D scanning technologies for investigations and scene preservation.

Outside of government applications, some of the most prevalent uses of 3D scanning in forensic investigations have been for accident reconstruction and fire origin and cause investigations. For example, if a fire expert needs to present his conclusions to a jury, he can utilize a 3D scan to digitally walk the jury through the scene, demonstrating details regarding the origin and cause of the fire. A 3D fly-through video of the fire scene can be used to help the jury understand the reasoning behind the expert’s conclusions.

However, the emergence of a wide-variety of affordable 3D scanning technologies has opened the possibilities of scanners to be used in forensic investigations beyond the traditional use of scene preservation. 3D scans can be used for a variety of analyses, ranging from stress analysis of a failed vehicle component to biomechanical analysis for personal injury cases.
Various types of 3D scanning technology are readily available on the market today. Scanners can range in cost from free phone apps to over $100,000 pieces of equipment. Expectedly so, the capabilities of these scanners also have a wide range; however, the common feature between all types of scanners is that they can all produce a 3D point cloud. A point cloud is the basic output of 3D scanning. In essence, a point cloud is a 3D representation of the scanned scene or object that is comprised of millions of individual points.

Point clouds can be generated for objects that range in size from small tabletop components to entire city blocks. The size, accuracy, complexity, and other features of the 3D scans are controlled by selecting different scanning technologies and parameters suitable for the investigation. For example, Figure 1 demonstrates how a scan of an exemplar person can be used to create a 3D point cloud and model of a human leg, which can then be transferred to analysis software for various attributes pertaining to the specific case.
Terrestrial scanners are commonly used for capturing large sites as a method of preserving the scene for future analysis. Some of these types of scanners can measure points over 350 yards away (up to 330 meters) and with accuracy up to ± 2 mm. The generated result is a 3D model of the scene that allows the investigator to virtually return to the location at a later date. Figure 2 is an example of a scene captured by a terrestrialscanner.

The top left image in Figure 2 is a scan of the site, which could be the scene of a vehicle crash. The site can be scanned several days after the incident during normal traffic conditions. Even though cars were driving through the scene during scanning, post-processing of the data was used to remove the aberrant vehicles and generate a clean scan of the location. The image in the top right of Figure 2 is a model of an exemplar truck scanned at another location. The model of the scanned truck can then be placed into the scan of the scene to create a digital reconstruction of the incident, as shown in the bottom image of Figure 2. The truck can then be placed in various locations within the scene, allowing the investigator to obtain highly accurate dimensions for different configurations, such as vehicle clearances to features within the scene. These types of point clouds can also be imported into software which can run simulations using the actual scene topography for accident reconstruction calculations and visualizations.

In comparison to terrestrial scanners, hand scanners and mounted scanners can deliver high-resolution models of smaller components, as shown in Figure 3. These high-resolution scans allow investigators to capture and document the conditions of subject components prior to disassembly or destructive examination.
The brake pads in Figure 3 were scanned with a high-resolution scanner and dimensionally analyzed for wear and warpage. The brake pads were constructed of wearable pucks adhered to a steel plate. Normal life of the brake pad would consist of uniform wear of the pucks until the height of the pucks was reduced to the steel plate (colored in blue), which would then require replacement of the brake pad.

A color map was overlaid on the scans of two brake pads with each color corresponding to a different height of the pucks in relation to the steel plate. The colors range from blue to red, where blue is at the surface of the steel plate and corresponds to a height of 0 inch, and red is a height of 0.4 inch which is the height of brand new pucks.

The top image in Figure 3 is of a model created from the scan of an exemplar brake pad, whereas the bottom image is of the subject brake pad involved in a fire. From the color maps, it can be seen that the new brake pad pucks are all at the same, uniform height. On the contrary, the subject brake pad steel plate was warped and the pucks were at different heights. By creating the color map of the puck height in relation to the warped steel plate, the wear pattern of the pucks was revealed. As can be observed in the image, the pucks wore down to the steel plate at the center of the plate where the warpage was the greatest. These 3D scans and dimensional analyses were used in conjunction with other metallurgical and mechanical analyses to determine the cause of the fire.

In addition to scene preservation and model analysis, 3D scans provide visual representations of scenes and conditions that can be essential in courtroom presentations through the creation of virtual walkthroughs and flyover videos. They also provide another tool to assist expert witnesses in presenting clear and concise engineering concepts.

As such, both litigators and investigators alike should consider utilizing this technology as new cases arise. Because, one thing that is certain in this ever-changing world of technology is that the prevalence of 3D scans in forensic investigations and trial presentations is sure to increase.