At the Scene of the Crime
September 3, 2006
Anyone who has seen the popular television show "CSI: Crime Scene Investigation" knows that technology now plays a key role in solving crimes. Most law enforcement officials, however, point out that technology alone-without the use of sound investigative methods-does not solve crimes. While we at Northway-Photomap acknowledge this to be true, we believe that offering our LiDAR (Light Detection and Ranging) services to law enforcement agencies improves their methods of collecting data. We are an aerial photography, mapping and land information firm located in Toronto, and we have been aiding forensic investigations with our terrestrial scanning services since 2001.
The purpose of investigating a crime scene is to reconstruct events in order to establish exactly what happened and to ultimately identify the perpetrator(s). When gathering physical evidence, attention to detail is critical. Essentially, the more details that are gathered, the better the chances of accurately reconstructing the scene of the crime and discovering "whodunnit." Traditional crime scene investigation often relies on cameras and conventional measuring devices to identify and locate evidence in the scene. LiDAR is an additional and complementary tool that aids this investigation. This article addresses some of the advantages of using LiDAR to help solve crimes.
Benefits of LiDARA ground-based LiDAR instrument uses a laser scanner to capture a complete three-dimensional image of a crime scene. Millions of laser points are used to build up a highly accurate spatial model of the scene in three dimensions: X, Y and Z complete with intensity. Newer systems integrate the ability to collect full RGB color registration for each of the points, resulting in an image with far more visual and spatial information than a two-dimensional photograph. Furthermore, the image is completely digital, which means that it can be viewed and analyzed from multiple perspectives. At Northway-Photomap, we own and operate an Optech (Toronto, Ontario, Canada) ILRIS (Intelligent Laser Ranging Imaging System) time-of-flight laser imaging system. The ILRIS fires 2,000 laser points per second in a 40Â° x 40Â° field of view. The resolution (shot to shot) is user-definable to allow for capturing details within the scene that may be obscured to conventional camera capture. The system has a 1500 nm laser wavelength and is Class 1 eye safe under all modes of operation (non-visible beam). The range capture envelope is from 3 m to 1,500 m, dependent on target reflectivity. Each laser point is matched with its respective pixel in the digital imagery captured from an internal six megapixel camera.
These ILRIS features provide us with the distinct advantage to classify an entire forensic scene. LiDAR covers the entire scene in a blanket of points, documenting not only evidence but contextual ambient factors as well. This data can be used in the initial planning stages and further analyzed for finer detail when gathering evidence.
A 3D scan of a crime scene is especially useful for processing evidence introduced or recovered after an initial investigation has concluded. For example, two months after a crime is committed, someone from an apartment adjacent to a crime scene might come forward to admit that she witnessed the crime taking place. If a highly accurate three-dimensional spatial model of the scene exists, it can be invaluable in corroborating (or refuting) the testimony of the witness.
Scanning to Solve CrimeWhen investigators require the use of our ILRIS scanner., it can be easily deployed by one person and set up within minutes of arriving at a crime scene. The range capture of the ILRIS and its field of view allow it to be placed at a distant vantage point (50 m) from the scene, thereby making it possible to capture 3D data covering a large area. Also, while the LiDAR scan is being completed, investigation within the scan area can continue without interference.
The efficiency of collecting this amount of 3D data far outweighs other conventional data gathering methods that can only acquire data in a 2D mode. Acquiring results in less than a few hours is usually invaluable to crime investigators.
Documenting the scene of a crime can be more challenging depending on the environment at the time of data collection. For example, collecting data at night can often obscure the view of objects that are readily identifiable in daylight. Ambient light conditions can impose strict limitations when conventional photography is used. A significant advantage of using LiDAR in the field is that it provides its own light source in the form of a laser. The active sensor is capable of collecting data at night or in conditions of poor light, and produces the same image intensity (grayscale), which eliminates color due to the absence of RGB from the camera. This enables investigators to discern details in objects based on their reflectivity characteristics. That is, the range capture of images via the ILRIS scanner is dependent on the amount of light energy that returns to the system once it hits a target. This energy is a function of laser wavelength, beam divergence (size of spot) and surface reflectivity. In the sample point cloud shown in Figure 1, pieces of evidence are readily identifiable. (Actual crime scene scans have not been published for confidentiality reasons.) Another advantage of using LiDAR in crime scene investigation is that it documents the current state of the scene, such as seasonal indicators and other conditions that may be relevant to the investigation.
Once we collect data, point cloud information is available and viewable within minutes. We use Innovmetric (Quebec, Canada) PolyWorks point cloud software to inspect the ILRIS data. The imported data is analyzed, and survey measurements are taken from the objects identified by numbered targets in the field of view. This information helps investigators to determine the validity of arguments in the case.
LiDAR is accurate to within 10 mm, and the 3D measurements taken from a scan aid in identifying line-of-sight locations for any witnesses who may have been present during a crime. Figure 2 demonstrates the results of documenting a crime scene using LiDAR point cloud data. All the spatial data is digital and in 3D format so that it can be viewed from different vantage points to help isolate any objects that may be crucial to the investigation.
Since the data collected through LiDAR scans is so detailed and dense, present and future developments in software technology will allow for the analysis and re-analysis of LiDAR data to provide further information. For example, blood spatter origin can be determined by the use of 3D LiDAR data. Typically, investigators return to the crime scene several times during an investigation to assess, reassess or gather additional information. LiDAR data and the collection of AVIs (Audio Video Interleaves, a multimedia video format that allows for animation and video manipulation of the captured 3D data) or data viewed through viewing software enables investigators to virtually return to the scene of the crime, take measurements, analyze, assess, hypothesize and deduce without ever having to leave their desks.
On certain scenes, our firm is challenged by a requirement to collect data from multiple vantage points (e.g., the roof of a building) to complete a 3D model of the image. At times and on certain projects, this may not be possible.
It may be very difficult to recognize in a scan the fine details or microscopic evidence that can only be documented using other technologies. But when it comes time to try a case in court, one strategic advantage of a LiDAR-scanned crime scene is the ability to graphically reproduce the crime scene or portions of it for presentation via rapid prototype printers. This enables judges and jurors to view evidence in a new and much more comprehensive manner. There are few images more revealing than a 3D fly-through of a scanned scene.
Creating 3D Models of the SceneThe advantages of LiDAR data collection in crime scene investigation include speed, efficiency, accuracy, depth of detail and digital storage for subsequent examination and analysis. LiDAR equipment can be indispensable when added to the crime investigator's toolkit. Though LiDAR does not replace conventional means of collecting data, it does offer a unique and highly effective tool for rapidly gathering very accurate spatial information that can be analyzed quickly. LiDAR technology will continue to evolve and improve the quality and amount of detail to help solve future crimes.
Sidebar: The Latest from Optech: The ILRIS-3D LineFor increased productivity at the crime scene, check out Optech's ILRIS-3D line of scanners. A compact and highly integrated package with digital image capture and sophisticated software tools, the ILRIS-3D addresses the needs of users on forensic sites.
The ILRIS-3D can be deployed by a single operator and requires no specialized operational training. Field deployment is made extremely efficient by ILRIS-3D's high data rate and wide range-from 3 m up to 1,500 m. In addition, the ILRIS-3D is completely eye-safe in all modes of operation.
Setup is rapid and simple-no leveling required-and the system is controlled via a wireless handheld PDA or laptop. The target area and scan status are displayed locally on screen, and data is written directly to removable media.
Optech also offers the ILRIS-36D, which features all the capability of ILRIS-3D with the added functionality of a 360Â° x 360Â° field of view. This enhanced coverage is provided by an integrated motorized pan and tilt base.
The ILRIS-3D line of imaging systems is ideally suited for crime scene investigation, offering true 3D imaging capabilities. ILRIS-3D products provide investigators with detailed digital data that can be reviewed and reanalyzed without ever having to revisit the crime scene. In addition, key evidence areas can be reconstructed in court for viewing by judge and jury. The ILRIS-3D and ILRIS-36D deliver high-quality data and fully quantitative metric evidence.
Sidebar: Crime Scene ConsiderationsTo ensure that a crime scene investigation is properly documented, it is important that the investigation methods are carefully planned in advance. Legal issues such as the need for a search warrant must be considered before entering a crime scene. Search warrants require short biographies of the people who need to enter the scene, as well as a description of the work they will do. Northway-Photomap has been working with the Toronto Police Service (TPS) for the past five years so we have an established an efficient protocol for working on forensic investigations. Those working in criminal investigation recognize that it is critical for the areas of interest to be quickly documented after a crime is reported. So when TPS wants us to do a scanning job, they will notify us and quickly set the process in motion.
In addition to the legal concerns, other factors must be taken into consideration when working on crime scenes. For instance, because we send employees to scenes where blood may be present, their Hepatitis B vaccinations must be current. We also allow our employees to opt out if they are concerned about working on potentially gory crime scenes, and we have a plan for what actions we will take if any of our employees are disturbed by the work. Ethical issues are also of paramount importance. Being named on a search warrant swears our employees to secrecy, and we must retain the trust of TPS when working on confidential cases.