Improve the NIBIN System by Providing Examiners a Capability to Match Infrared Images of Firing Pin Impressions and Deformed Bullets as well as Accurate Large Database Searches
Francine Prokoski, Ph.D.
Abstract
This grant effort was focused on improving the National Integrated Ballistic Information Network (NIBIN) System by providing examiners with advanced capabilities to:
- identify cartridge casings by using infrared (IR) images of firing pin impressions (FPI),
- identify bullets by using IR images of land impressions
- perform accurate high-speed search of a large database to identify fired cartridge casings.
- This report summarizes successful accomplishment of those goals. Reviewers of the draft
- version of this report found the research effort provided a compelling proof of concept
- demonstration of the effectiveness of IR imaging for toolmark identification, and made a very
- significant contribution by showing an underlying scientific basis that can be quantified and
- statistically measured. The use of IR imaging offers reliable and significant improvement in case
- linkage supporting forensic firearms examinations.
The project was divided into three separate but related efforts:
- Determine the persistency of firing pin impressions (FPI) by collecting 1,000 cartridge cases fired in each of 8 different firearms
- Conduct a Proof of Principal using IR to accurately match fired bullets bearing minimal damage collected from sample firearms
- Build a large database of cartridge cases and be able to locate siblings. This database contains multiple fired cartridge cases from an unknown number of firearms
Historically, examiners have attempted to link shooting incidents using evidence from a current shooting to that from a past shooting. The volume of evidence forced the introduction of technology. By the late 1980s computer-based case linkage systems became a reality. These advances improved evidentiary analysis and fostered the production of first generation ballistics- type workstations for case linkage and the networking of visible light systems serving the majority of forensic laboratories. The predominant system today is the Integrated Ballistics Identification System (IBIS), networked under the umbrella of the National Integrated Ballistic Information Network (NIBIN).
Under this grant, two-dimensional infrared (2D/IR) and three-dimensional infrared (3D/IR) analysis of firing pin impressions (FPI) was performed. The persistence of FPIs, imaged with IR cameras, demonstrated IR imaging provides details of deep firing pin impressions that cannot be seen using visible light. Use of IR imaging demonstrated firing pin impressions remain relatively constant for a selection of firearms and ammunition during the sequential firing of 1000 rounds of ammunition. 3D/IR analysis of cartridge cases from certain firearms may also provide a reliable determination of firing order among sibling casings collected from a shooting scene. That could be a significant aid to crime reconstruction.
IR imaging demonstrated a high degree of effectiveness for the comparison of fired bullets (pristine and minimally damaged) to identify siblings fired from the same firearm. Additional comparison techniques included three-dimensional pattern recognition and feature metrics. Techniques for comparing bullets proved similar, producing a high degree of confidence and significantly reducing the number of false positives compared to reported performance of current NIBIN workstations.
Improved performance was achieved by the use of IR imaging and an advanced pattern matching engine called FlashCorrelation®. This approach to pattern matching results in rapid locally- controlled image correlations based on the superior detail in IR images and the application of FlashCorrelation®. The ability to image, store, and accurately identify sibling cartridge cases from a large database of infrared images was clearly demonstrated. When a sibling was present in the database of 2000 Glock 9mm casings, its Match Value was ranked #1 for 99.5% of tests and was in the top three positions 100% of the time.
A database of fired cartridge cases was expanded to determine the scalability of the infrared image comparison techniques. A statistically significant sampling of infrared images was utilized for comparison purposes. Fired cartridge cases were primarily collected from common handguns: Glock and Hi-Point. The Hi-Point company provided fired cartridge cases and bullets from more than 100 handguns. Personal contacts allowed access to several hundred Glock cartridge cases that were entered into an established database involving many Glock firearms with known linkage to other fired cartridge cases. AR-15 and SKS rifles were also selected for examination and analysis.