Cartridge casings found at crime scenes may contain fingerprint evidence to introduce or help convict a suspect; however, there are few articles on the subject of the best method to develop fingerprints on cartridge casings. The purpose of this research was to compare the best development methods for unfired casings found in previous research along with other commonly used development methods. After the most effected method was determined, that method was then applied to fired brass cartridge casings. Five different methods and five hundred unfired .40 caliber brass cartridge casings with one fingerprint on each were used. The two techniques that yielded the best results were cyanoacrylate fuming followed by gun blue followed by BY40 and cyanoacrylate fuming followed by BY40 followed by acidified hydrogen peroxide. The technique that produced the highest average of fingerprints of comparison value was cyanoacrylate fuming followed by gun blue followed by BY40; this method was the method chosen to be applied to the fired cartridge casings. Phase II consisted of firing fifty .40 caliber bullets from a .40 caliber handgun after one sebaceous fingerprint was placed on each casing. Although cyanoacrylate fuming followed by gun blue followed by BY40 yielded clear fingerprints with unfired casings, this method did not produce any clear fingerprints on fired cartridge casings due to the factors a casing sustains during the firing process.

Introduction

Fingerprint comparison and examination has been used to connect suspects to evidence and crime scenes since 1892, when a trial in Argentina used a bloody fingerprint found at a crime scene to convict Francisca Rojas of murdering her two children (Lee and Gaensslen 2001). The science behind fingerprint examination involves the patterns of ridges and furrows found on the palms of the hands and the soles of the feet. These ridges have pores that secrete perspiration, and when a finger comes in contact with an object, the perspiration can leave an impression of the ridges. The use of fingerprint comparison to convict a suspect relies on the concept that ridges of a fingerprint remain the same over the course of one's lifetime, and that no two people have the same fingerprint (Lee and Gaensslen 2001).

The National Institute of Justice describes three different levels of detail used to describe the characteristics of a fingerprint. First level detail describes the overall direction of ridge flow in a print. A print described using first level detail would be classified as a loop, arch, or whorl. First level detail is a class characteristic and cannot be used for individualization. Second level detail describes the path of an individual ridge. Ridge endings and bifurcations, where one ridge splits into two, can be seen if second level detail is present. Second level detail can be used for individualization. Third level detail includes the morphology of a ridge. The texture and position of pores of the ridges can be seen if third level detail is present (NIJ 2011).

An example of evidence that could contain fingerprints is cartridge casings. Before a bullet and its casing are loaded into a gun, it is presumably handled and marked with fingerprints. After the bullet has been fired, its casing is ejected from the gun. If not retrieved, this casing is left at the scene. Fingerprints left on casings found at a crime scene could be evidence to introduce or help convict a suspect. However, there are few articles on the subject of the best method to develop fingerprints on brass cartridge casings.

Fingerprints are rarely recovered from fired cartridge casings due to the factors a casing sustains during the firing process. One factor affecting the likelihood of developing a fingerprint from a casing is the friction between the casing and the gun through the firing process. Friction occurs between the magazine and casing as the casing is loaded into the magazine. Friction also occurs when the casing enters the chamber before firing and when the casing is ejected from the chamber after firing. The casing is exposed to high temperatures and combustion gases during the firing process that can affect the oils and sweat from a fingerprint on a casing that would be used in development (Champod et al. 2005).

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