INFLUENCE OF PROJECTILE MATERIAL ON THE EFFECTIVENESS OF AUTOMATED COMPARISON

Lehi Sudy dos Santos¹; Palloma Vieira Muterlle¹

¹ University of Brasilia

doi:10.20906/CPS/COB-2015-1244

Resumo

When a crime is committed with a gun, forensic experts may have to match fired bullets from the scene with each other, or with a firearm. Although this kind of exam has been done for almost a hundred years, being successfully used in countless cases, it has some limitations. Among them the fact that the analyses are made by the comparison of two specimens at a time in the microscope, which leads to a very cumbersome and time-consuming process, particularly when many specimens are related to the same crime, and that in many situations there is no questioned firearm, which leads to an open case. In order to reduce the time spent in the comparison process and to better deal with open cases, forensic labs all over the world have tried to implement electronic comparison systems. To assess the feasibility and accuracy of a future National Ballistic Database, a reference ballistic image database (RBID), using the Ballistic Identification System Evofinder®, has been implemented with test-fired bullets from revolvers on the caliber .38SPL. The hit-list for controlled comparisons, involving projectiles of different materials, were used to derive quantitative effectiveness criterion proposed by Joachim Rahm (2012). The results showed huge differences in system performance between different projectile materials. Brinell hardness tests on the bullets were made to investigate the influence of this parameter on the effectiveness of the system. The results provided a guide to the projectiles that must be used, when colleting samples from a gun, in order to ensure a higher effectiveness criterion and consequently the best correct gun identification probability.

Palavras-chave: Firearm; Evofinder; Automated comparison; Bullet; Correlation quality