short pattern testing in crime scene in forensic science

short pattern testing at crime scene

1. PRESENTATION ON SHOT PATTERN TESTING IN CRIME SCENE RECONSTRUCTION SUBMITTED TO. SUBMITTED BY KURUKSHETRA UNIVERSITY DIVYA RANI ROLL. NO.5 CLASS M.Sc. FORENSIC SCIENCE KURUKSHETRA

2. Content Introduction Shooting crime scene reconstruction Shot pattern testing Procedure Factors affecting shot pattern Uses of shot pattern testing Forensic aspect Case study Conclusion References

3. Shooting CRIME SCENE RECONSTRUTION Reconstruction of a shooting incident relies on careful examination and processing of a scene for pertinent physical evidence including defects and holes caused by projectiles. Accurate reconstruction typically requires the identification and collection of associated evidence and its subsequent analysis in the Laboratory.

4. SHOT PATTERN When a shot charge leaves the muzzle of a gun the pellets cluster together and do not separate to any appreciable extent until they are from 3to 4 feet from the muzzle. When they begin to spread outwards and so cover an ever increasing area as the range becomes greater. The degree of spread is approximately proportional to the range .

5. Procedure of shot pattern testing: Securing of scene Photography Documentation of all evidences. All evidences like wads, cartridge case are packed in different paking boxes for preventing transfer of evidence. Then the crime scene investigator analyse the pattern for identifying the distance between the victim and the shooter. For analysis the test Firing is done

6. Test Firing Patterning can be done with simple, homemade targets—sheets of blank paper about 4 x 4 feet in size. Fire one shot at the center of the target (or bull’s-eye) from the distance that you expect. Repeat this two more times, each time with a new sheet of target paper. On each of the three targets, draw a 30-inch circle around the densest part of the shot pattern.

7. On each of the three targets, count the number of pellet holes that fall within the 30-inch circle, marking them with the marker as you count each one. Average the pellet counts within the 30-inch circles (add the three counts from the previous step, and divide the sum by three). Then divide the average pellet count by the number of pellets in the load for the ammunition you are using, and multiply this result by 100.

8. Factors affecting shot pattern testing Pressure: The higher the pressure the more pronounced is the scattering effect on the pattern. Velocity: high velocity help to make the pattern scattered and irregular while a low velocity helps towards an even distribution and an increase in density . Shot size: The smaller size pellets acquire greater muzzle velocity .

9. Choking A constriction in the end of the barrel known as the choke is used to tailor the pattern for different purposes. Cylinder choke is an unconstructed barrel. The shot string spreads quickly. Improved Cylinder choke has a slight constriction. It allows the shot string to spread fairly quickly. Modified choke has moderate constriction. The pellets stay together longer, making the shot string denser and more useful at longer ranges

10. Full choke: Full choke has tight constriction. Reduction in diameter of barrel at muzzle end upto 1mm.Spreading Of pallet at site upto 70cm in circles

11. Uses of shot pattern testing Determination of distance between the victim and the shooter . The distance from which a shot has been fired is calculated from the presence or absence of scorching , singeing, blackening and tattooing. Scorching is also known as burning or charring. Scorching is the discoloration resulting from burning by the flame or hot gases that issue from a firearm. Scorching is an clear indication that the shot has been fired from close range.

12. Singening Around the wound upto a shot distance the hairs due to flame are burned and singed. Blackening is also an smudging. Blackening generally consist , wholly or largely, of smoke produced by the combustion of the powder. Tattooing It is caused by the embedding of unburnt or semiburnt powder particles into the surface of the target.

13. Direction of fire estimation The direction of fire of a shotgun can only be determined from the entrance wound . From a medico legal standpoint it is usually more important to establish the direction of fire. If the bullet has passed through the body , the direction of its flight may be established by recognizing which wound was the entrance and which the exit. The entrance wound is smaller than the exit wound.

14. Forensic aspects of shot pattern testing. Shotgun pattern testing play very important role in the determination of distance between the victim and the shooter. By knowing the type of wound present Ion the surface the investigator get idea that what is the distance between the victim and the shooter. Also by knowing the shape and size of wound the direction of firing also determined.

15. Case study

16. Conclusion

17. Reference