Ballistics 8

Lecture 8

Techniques used to analyse gsr

-       Visual Examination

-       Infra Red Photography

-       Soft X-Ray Radiography

-       Dermal Nitrate Test

-       Walker’s Test

-       Harrison and Gilroys Test

-       Prince Spot Test

-       Neutron Activation Analysis

-       Flame-less Atomic Absorption Spectrometry

-       Scanning Electron Microscopy

Examination

Visual Examination

Infra Red Photography

Soft X-Ray Radiography

Dermal Nitrate Test

Walker’s Test

A desensitized glossy bromide paper is taken. It is treated with 2 naphthyl-amine 4: 8-disulphonic acid (5%). The bromide paper is placed over a table with the treated surface on top. The cloth bearing the gunshot residues is placed over the bromide paper. It is covered with a towel moistened with 20% acetic acid and the arrangement is pressed with a hot electric iron for about five to ten minutes. Dark red spots on the bromide paper indicate the GSR.

A modified version of the test is as under:A piece of filter paper is moistened with acetic acid. It is pressed against hthe target surface. It picks up the gunshot residues. The filter paper is then sprayed with a solution of 2 naphthylamine sulphanilic acid and citric acid.The pink coloured specks indicate nitrite particles. They, in turn, indicate GSR.

Walkers test is useful to

o   Identify the bullet entrance holes and wounds.

o   Determine the range of fire.

o   Ascertain whether a firearm, bullet, cartridge, etc., has been fired or not.

o   Estimate the approximate time of fire. The diminishing intensity of the color formed is the indicator of the time elapsed.

o Identify a shooter.

Harrison and Gilroy’s test

Harrison and Gilroy's test determines the presence of lead, antimony and barium through spot test. The gunshot residues containing the metallic constituents are collected on a piece of cotton cloth (moistened with dilute hydrochloric acid). The cloth is, then, tested as under:

o   A dried piece of test cloth is treated with one drop of triphenyl methylarsonium iodide alcoholic solution (10%). The appearance of an orange ring, in about two minutes' time, indicates the presence of antimony.

o   The test cloth bearing the orange ring is dried and two drops of sodium rhodizonate solution (5%) are put in the centre of the ring. Red colour development, inside the ring, indicates lead, barium or both.

o   The test cloth is dried again. A drop of dilute hydrochloric acid (1 : 20) is placed on the red spot developed in (2) above. If the colour changes to blue, lead is indicated. If the colour does not change, barium is indicated.

Price's Spot Test

This technique involves the identification of lead through a standard spot test using, sodium rhodizonate solutions. The gunshot residues are collected from the hands on a piece of cloth moistened with 1% hydrochloric acid. The test does not offer any advantage over Harrison Gilroy's test.

Neutron Activation Analysis

The examination of gunshot residues by Neutron Activation Analysis depends upon the presence of antimony and barium. When the gunshot residues are exposed to neutron bombardment in a nuclear reactor, antimony and barium capture one neutron each, to give radioactive antimony and radioactive barium

The radioactive nuclides emit gamma rays. Evaluation of the energy and hall life help identify and estimate the isotopes. The estimation is usually done by comparing with the standards. Neutron activation analysis is a highly sensitive technique. However, it is cumbersome:

o   It needs a reactor for the neutron source, which are scarce.

o   It is time consuming.

o   It needs a lot of pre and post-activation chemical treatment of the samples. For example, sodium and chloride ions from perspiration have to be eliminated for proper estimation.

o The technique is not suitable for analysis of lead, which is the most important metallic constituent of gunshot residues.

Flame-less Atomic Absorption Spectrometry

It can detect the elements in nanogram and picogram ranges. Atomic absorption spectrometry works on a very simple principle. An element absorbs the radiation of the same wave length as it emits when excited. The suspected element (in gunshot residues) is taken into an atomiser (a graphite tube or a Tantalum strip) and is excited by heating. The radiation from a discharge tube with the suspected metal electrodes is passed through the atomiser. The loss of intensity in radiation gives the measure of the quantity of the metal in question. The technique is useful and popular for the examination of the gunshot residues. It is less costly, consumes less time and is applicable for lead estimations also

Trajectory analysis and reconstruction of crime scene

1.     Initial Conditions:

Firing Position: The location from where the firearm was discharged.

Angle of Fire: The angle at which the firearm was held relative to the ground and target.

Projectile Type: Characteristics of the bullet, including calibre, weight, and shape.

2.     External Ballistics:

Flight Path: The trajectory of the bullet through the air, influenced by gravity, air resistance, and other environmental factors.

Intermediate Targets: Any objects or surfaces the bullet might have encountered along its path, such as walls, furniture, or glass.

3.     Impact Analysis:

Entry and Exit Wounds: The analysis of wounds on the victim to determine the bullet’s trajectory through the body.

Terminal Ballistics: The study of the effects of the projectile on the target, including penetration, fragmentation, and energy transfer.

Tools and techniques

-       Laser Trajectory Kit: These kits use lasers to simulate the bullet's path, helping investigators visualize the trajectory from the point of fire to the point of impact.

-       Rod and String Methods: Rods or strings are used to physically recreate the bullet’s path through space, especially useful in indoor shootings where the path can be confined by walls and ceilings.

-       Ballistic Software: Advanced software can simulate the trajectory based on input data such as the type of firearm, ammunition, and environmental conditions. These simulations help in visualizing the flight path in 3D.

Applications in investigations

-       Determining Shooter’s Position

-       Reconstructing Crime Scenes

-       Assessing Self Defense Claims

-       Correlating Evidence

Stages of reconstruction

Data collection

Conjecture

Hypothesis formulation

Testing

Theory formation

Shooting scene reconstruction

-       Witness interview if any

-       Range of fire

-       Angle of fire

-       No. of weapons used

-       Type of weapons used

-       Trajectory of projectile

-       Identification of entry & exit hole

-       Sequence of event

Serial Number Restoration

o   Grinding or Filing: Physical removal of the numbers.

o   Punching or Drilling: Creating indentations to obscure the numbers.

o   Chemical Etching: Using acids or other chemicals to dissolve the numbers.

o   Welding or Over stamping: Adding material or new stamps over the original numbers.

Restoration Techniques

Magnetic Particle Inspection

Chemical Etching

Electrochemical Methods

Heat Treatment

Ultrasonic Cavitation