Gunshot Residue (GSR) Evidence

Introduction

Gunshot residue (GSR) evidence is an area of forensic science that is often underestimated and underappreciated by the forensic scientists. When ejecta gets deposited on any surface after firing, it is known as GSR. Surface may be any target, barrel or the shooter. During firing at the time of flight ejecta is formed. They may be found on the shooter’s hand. These are various sources of ejecta particles. The deposition of GSR deposition is used to determine the range of firing and time of firing. Ejecta is the material or component coming out from the muzzle along with bullets during a fire. Ejecta has bullet, flame, partially burnt or unburnt particles, metallic chips, smoke and gases as the major components.

Transfer of Gunshot

This event occurs in a fraction of a second and creates what we known as GSR, as well as other things. Particles are deposited on the hands, clothing, and surrounding areas on or near the shooter. The basic principle of trace and transfer evidence is the Locard Exchange Principle. When one considers GSR evidence, as the firearm is discharged, the particles formed from the combustion, products of the ammunition component, transfer to the surrounding area. Unlike most transfer evidence, no direct contact is made between the hands and the airborne particulate. The particulate is simply deposited on the hand of shooter or surrounding surfaces. The GSR can be transferred from the backs and palms of the hands to other items simply by rubbing the hands together or transferred from hands into pockets. A brief summary of key areas of GSR deposition follows.

Hands — The hands are the most common places from where GSR is collected from suspected shooter. With firearms, such as revolvers, pistols, and automatic weapons, a clear pattern emerges as to the areas of greatest GSR

Washing with HNO3- hands are washed in plastic bags containing dill. HNO3. Maximum upto concentration of 5% in the tap water. This process is done maximum up to 30 seconds, not beyond that. The dissolved solution is sent for further tests.

Examination of GSR

Chemical Tests

1. Paraffin test- hands are coated with paraffin. After cooling of paraffin, the cast is removed and treated with diphenylamine solution. The presence of blue flecks indicated the presence of nitrites and nitrates. This test gives positive results in the absence of GSR because the both chemicals are present in the environment in large quantity which affect the results. So, this test has no scientific and not used in forensics.

2. Harrison-Gilroy Method- cotton swab, moistened with 0.1M HCL is used to collect GSR from the shooter’s hand web and treated with 10% triphenylmethylarsonium iodide. Development of orange color confirms the presence of Antimony (Sb). On the orange ring 5% sodium rhodizonate is added. Red color formation shows the presence of Barium (Ba) and Lead (Pb). On the red color spot HCL is added after drying the swab. If it turns into blue, it confirms the Lead and no change in color confirms the Barium.

Instrumental