Using iWitness to map bullet trajectories


Background

Police investigators and forensic scientists face challenges in obtaining accurate measurements when documenting crime scenes. Often the incident is in cramped quarters, and 3D mapping amounts to a difficult task. In many cases, it is unfeasible or nearly impossible to map the crime scene with a total station theodolite due to unstable flooring, line-of-sight issues and limits of the size of the room requiring the instrument setup. Baseline tape measurements are often inaccurate for 3D data, as well as even 2D mapping tasks. Once the crime scene investigation is vacated, there is seldom a chance to go back for other 'missed' evidence data, without the evidence being possibly compromised.


iWitness close-range photogrammetry is often the preferred method of forensic measurement and mapping tasks over other technologies for these reasons:

  • Faster evidence acquisition – reduces mapping time and law enforcement overtime at the crime scene
  • 'Non-contact' data acquisition
  • Ease-of-use in confined quarters
  • No issues with vibration, which, conversely, is an issue for total stations and 3D passive lasers
  • Creates a permanent archival of the crime scene for additional measurements long after the scene is cleaned up
  • Extremely accurate 2D and 3D data acquisition
  • Advanced 'network stitching' tools links photogrammetric networks together. iWitness is the industry leader in photogrammetric camera orientation and triangulation processing
  • Works well with CAD packages, such as CAD Zone Crash Zone and is the easiest photogrammetry program on the market to use by non-photogrammetrists
A Real-World Homicide Mapping Case

DeChant Consulting Services coordinated with the Washington State Patrol to map critical evidence in a homicide investigation, using iWitness after the completion of the on-scene photography. A Kodak DCS420m (monochrome) digital camera was used for the photogrammetry picture taking.


The incident involved one murder victim. Three rounds were fired at the crime scene. The digital photography time was 25 minutes in order to acquire enough overlapping photos to map the entire living room/kitchen area, as well as the bedroom and bathroom areas.


The purpose of using iWitness in this homicide case was to map the critical evidence accurately and to document the scene in case other evidence was later required for further measurement analysis. Although many objects were mapped using iWitness, of primary mapping concern was the bullet holes, victim’s location, as well as blood splatter and blood pool areas.


Real world forensic scene and bullet mapping

iWitness measured entities in CAD

The Results

iWitness mapped with flawless precision for the crime-scene evidence using the digital images taken at the scene. The bullet trajectory angle through the sheetrock of the two walls of the rooms was accurately measured, as were the mapping locations of additional pieces of critical evidence. The results of the iWitness photogrammetric 3D model were scaled and rotated to a plan view and exported to a CAD diagramming program. The iWitness results produced an extremely accurate and detailed mapping of the crime scene.


iWitness is an important tool in forensic mapping applications for police and accident reconstructionists. It is the best in the field of close-range photogrammetry and is superior to other measurement and mapping technologies at a fraction of the cost.

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