# Comparative Analysis of LiDAR and Photogrammetry for 3D Crime Scene Reconstruction
## 1 Introduction  
Accurate and reliable three-dimensional (3D) mapping information is paramount in crime scene investigations. Once a crime is committed, the crime scene is a witness to illicit acts that occurred in it. It contains data and information, in addition to other forms of evidence, and all should be collected accurately and precisely to ensure that justice is served [1, 2, 3, 4]. However, investigators' initial encounter with the crime scene is usually challenging, especially for first responders, who are responsible for the preservation of the scene's integrity, with no contamination being allowed, and all objects on the scene that could be of use as evidence must be collected as soon as possible [2, 4]. Traditional manual measurements tools have been widely utilized to document the crime scene content, such as rulers, measuring tapes, and photographs, to document all essential aspects of a crime. However, they struggle to capture all of the crime scene details, posing a challenge in terms of practicality, accuracy, and total comprehensiveness of the crime scene [5, 6, 7, 8]. Moreover, manual easements are time-consuming, especially with more extensive scenes, prone to human error, and require the collaboration of a properly trained team to finish the work swiftly. While traditional tools are used and accepted in legal proceedings, the rapid development of 3D-modeling technologies, particularly LiDAR (Light Detection and Ranging) scanners [1, 3], can be found not only in professional-grade scanners but also in more affordable consumer-grade scanners, such as the iPhone built-in LiDAR sensor [9, 10, 11, 5, 12, 13]. Image-based photogrammetry technology also offers a higher level of accuracy with details plus the fast speed and beyond provided by the traditional methods [4; 14; 15; 16; 17; 18]. LiDAR technology involves emitting laser beams to scan the surveyed area and calculating the time it takes the laser beam to return to the sensor. This technology has been used vastly in many fields with highly accurate results, and, thus, it has been studied for crime scene investigation [1]. On the other hand, photogrammetry employs photography to capture images, combines them together, and builds a three-dimensional representation of the photographed area [4; 14]. Like LiDAR, photogrammetry has found significant applications in forensic science, where it aids in reconstructing crime scenes, allowing forensic experts to analyze crime scenes with high spatial accuracy, enabling a better understanding of the events that occurred without needing a physical presence [4]. Moreover, photogrammetry can be more practical than LiDAR in some cases, since most mobile phones have cameras but do not have LIDAR sensors. Although LiDAR and photogrammetry technologies have been utilized for crime scene applications, they still lack the thorough evaluation of the recent iPhone LiDAR and photogrammetry technologies in a realistic crime scene with challenging illumination and scanning time [10; 18]. In this work, we evaluate the recent mobile phone-based LiDAR and photogrammetry technologies for a mock-up crime scene, as shown in Figure 1, in which an Apple iPhone 15 Pro Max and a LEICA BLK360 (Lecia Geosystems, Heerbrugg, Switzerland) are used for LiDAR mapping, while the same phone is used for photogrammetric mapping for comparison. The LEICA LiDAR is used to compare the point cloud accuracy, which is crucial to understand the accuracy of 3D maps. The mock-up crime scene was professionally prepared by crime scene investigators and has been utilized for training law enforcement officers in the institution. The significance of this study lies in its attempt to enhance crime scene evidence documentation by evaluating recent mobile 3D reconstruction technologies. Figure 1: A mock-up crime scene, showing a mannequin, markers, blood spatters, and a LIDAR scanner for ground truth comparison. The scene was prepared by crime scene professionals and has been utilized for training law enforcement officers.