The use of 3D laser scanners isn’t new to the field of forensics, but it is one of the most rapidly growing markets. Sessions dedicated to forensic applications can now be found at just about every laser scanning conference, and the rooms are usually packed. Although scanners were originally developed for the survey market, the technology lends itself well to documenting crash and crime scenes and has been readily accepted by the law enforcement community.
The reason for this acceptance comes down to efficiency. On major crash or crime scenes, one of the most time-consuming processes for investigators and crime scene technicians is documenting the scene, including photographing, logging and measuring the location of the physical evidence. This work was originally done by hand and was later expedited with the use of a total station. Then, in the early 2000s, law enforcement agencies began using laser scanners to gain further efficiencies. Today, there are still instances when both total stations and laser scanners are needed to successfully document the entire scene. For example, the scanner may not pick up faint tire marks at the scene of a collision if there isn’t enough contrast between the tire marks and the roadway surface. However, for most major scenes, laser scanning is now considered the quickest, most accurate and most reliable way to document the scene and the surrounding environment.
An advantage to laser scanning is that all the data is preserved; the scan represents the scene as it was on the day it was captured, much the same way that a photograph captures a moment in time. Once scanning is completed and the data is processed, law enforcement professionals can revisit the crime scene on their computer as often as needed throughout the course of their investigation. If they need to take measurements or verify information, they can do this in the office. If they need forensic analysis that is outside their area of expertise, they can share the data with other experts who can use it to reconstruct the crime scene and even create 3D forensic animations. However, the vast amount of data collected with modern laser scanners also presents its own challenges in forensic applications.
Most drawings created for criminal court are top-down 2D diagrams that represent the scene and the physical evidence. In some instances, a 3D drawing is necessary to show a better representation of the actual scene as well as to show the results of any analysis based on the point cloud data. When law enforcement agencies began purchasing scanners, they quickly discovered that there was not an easy way to produce a deliverable product in the form of a drawing from the point cloud.
In June 2010, MapScenes Systems introduced a solution with the release of PointCloud 2010. Other forensic software developers are not far behind in releasing their versions of point cloud software.
MapScenes PointCloud 2010 has three separate components. PointCloud allows the user to import and visualize the point cloud and provides a variety of tools to aid in creating a drawing. Forensic CAD is a stand-alone drawing package used to draw in 2D or create 3D models. And Capture is the animation module for creating an animation either within the point cloud or as a stand-alone animation.
For crash reconstruction, it is sometimes necessary to create a damage profile of a vehicle in order to determine the depth of the crush to a vehicle or how two vehicles were oriented to each other at impact. This data is used to calculate the energy that caused the damage and ultimately to determine the speed of the vehicle. If the damage profile of the vehicle shown was measured with a total station, the measurements would likely be taken at bumper height around the entire vehicle. With a laser scanner, the entire vehicle can be documented and the crush line can later be measured at any height. A Profile Slice Tool in MapScenes PointCloud 2010 allows the user to create a damage profile at varying heights around the vehicle.
Proper training is essential for anyone planning to use laser scanning in forensic applications. Although today’s equipment can be relatively easy to use, there are pitfalls. In criminal court, where the data can take away someone’s freedom, it is imperative that the people involved know what they are doing.
The role of the forensic investigator using scanning technology is different from that of other users. The operator and the methods used fall under greater scrutiny. Although 3D laser scan data is admissible in court, no defense attorney will allow laser scan data to enter the proceedings without a fight unless his or her client will benefit from it. It is up to the investigator to get the data qualified. If the scan data is excluded from the court proceedings, any drawings, analysis and opinions that were derived from the data will not be admissible.
The forensic investigator will likely be required to explain how the equipment works as well as how the operator knew the equipment was measuring accurately. Producing a calibration certificate may not be sufficient. This issue has come up in forensic mapping with the use of a total station. In forensic mapping courses, the operator is often trained to take a measurement to a known distance at the start of the mapping project. At the end of the project, the operator takes a second measurement to the same point and compares the two measurements. If the measurements are within an acceptable tolerance, then the operator can reasonably conclude the equipment was measuring properly during the project. Similar concepts can be applied in laser scanning training: The operator of the scanner can scan targets placed at a known distance or can take hand measurements to two or more recognizable points in the scene and later verify these measurements from the point cloud data.
Most crime and crash scenes require multiple scans from multiple locations. These scans must be stitched together in a process known as registration, which can introduce errors. Additionally, every measurement will likely have some error. Both the registration process and common errors should be covered in detail during training so that the user has a firm understanding of the process. Scan operators who are involved in court proceedings need to know how to testify regarding the accuracy of their scan data as well as the errors.
The best source of training is someone who has a forensic background or at least a clear understanding of the needs of this market. The trainer should be available for technical support in case the operator encounters problems in the field or in the office when they are processing the scan data.
It is not possible to learn everything about scanning in one training session. Operators should obtain enough training so that they can successfully operate the scanner and software, and then spend some time in the field using the equipment. They should then follow up with some additional training to cover advanced topics.
Every law enforcement agency will need to have access to a scanner at one time or another for a major incident, but not every agency is able to afford to purchase a scanner and train their personnel. In some cases, equipment funding can be found through grants. Other agencies may be able to use asset seizure money to purchase equipment. Smaller agencies can sometimes partner together through multi-agency agreements to purchase the equipment and required training.
In other situations, an agency might be able to arrange for a nearby agency that has a scanner to respond in the event of a major incident. Another option is to consider renting a scanner and hiring an experienced operator to use it.
Bringing scan data into the courtroom allows the audience to visualize the scene as it existed at the time it was scanned. Nothing captures the jurors’ attention like a visual presentation. By using tools such as fly-through animations, an investigator can virtually walk the audience through a tour of the scene as well as present viewpoints from the defendants, victims and witnesses. In a major case, such as an officer involved shooting or an officer involved in a collision, having the scene properly documented is money well spent.
When it comes to using 3D laser scanners in forensic applications, we are just scratching the surface of this technology. As more and more agencies begin using scanners, the way they use the technology will continue to change as they begin to develop experience and experiment with different techniques. This will lead to further improvements in scanning hardware and software--and an even greater demand for laser scanning to document crash and crime scenes.
For additional information about MapScenes software, visit www.mapscenes.com.