Firearms, Tool Marks, and Other Impressions

1. Firearms, Tool Marks, and Other Impressions Objectives: Describe techniques for rifling a barrel. List the class and individual characteristics of bullets and cartridge cases. Explain the utilization of the comparison microscope for the comparison of bullets and cartridge cases. Distinguish caliber from gauge. Created by C. Ippolito April 2008

2. Firearms Identification • concerned with determining whether a bullet or cartridge was fired by a particular weapon • bullet  gun • structural variations • irregularities • scratches & nicks • breaks & wear • more than bullet comparisons • weapons operation • restore obliterated serial numbers • detect & characterize GSR • determine muzzle-to-target distance Created by C. Ippolito April 2008

3. Gun Barrel Manufacture • made from solid bar • hollowed by drill • random marks left • followed by rifling • grooves on inner surface • “twist” bullet for straighter, more accurate path • rifling methods • hook cutters – rotated – forms spiral groove – 1 at a time • broach cutter – concentric rings – simultaneous cuts all • button process – metal plug compresses sides • mandrel process – barrel hammer from outside down Created by C. Ippolito April 2008

4. Gun Barrel Terms • Bore • the cavity inside the barrel • Rifling • spiral grooves in bore • spins projectile • Groove • cut/low-lying parts of rifled bore • Land • uncut/raised parts of rifled bore • Caliber • diameter of the bore • hundredths of an inch (.22) • millimeters (9mm) Created by C. Ippolito April 2008

5. Bullet Markings • Class Characteristics • lands • grooves • twist direction • General Rifling Characteristic File • FBI data base of class characteristics • Individual Characteristics • striations • fine lines caused • minute imperfections on cutters • steel chips from cutters • Comparison Microscope • tool used to compare bullets Created by C. Ippolito April 2008

6. Shotgun Barrel • smooth bore • groove would spread pellets • gauge • diameter of barrel • # of lead balls with diameter = to bore of barrel that would weigh 1 lb Created by C. Ippolito April 2008

7. Comparison of Cartridge/Shotgun Shell Created by C. Ippolito April 2008

8. Cartridge/Shell Markings • Breechblock • rear part of barrel • marks base of cartridge/shell • Firing Pin • strike mark on base of cartridge/shell • Ejector/Extractor • mechanism that removes cartridge/shell from chamber • leaves unique striations Created by C. Ippolito April 2008

9. Firearms, Tool Marks, and Other Impressions Objectives: Explain the NIBIN data test system. Explain the procedure for determining at what distance from a target a weapon was fired. Describe the laboratory tests utilized for determining whether an individual has fired a weapon. Emphasize the limitations of the present techniques. Explain why it may be possible to restore an obliterated serial number. Created by C. Ippolito April 2008

10. Automated Firearm Search Systems • DRUGFIRE (FBI) • unique markings on cartridge cases • microscope images captured and digitalized • Integrated Ballistic Identification System (ATF) • Bulletproof • bullet analyzing module • Brasscatcher • cartridge analyzing module • National Integrated Ballistic Identification System • 1999 the two systems combined Created by C. Ippolito April 2008

11. Gunpowder Residues • Distance determination • distribution of powder/pellets • calculate firearm distance from target • Handguns and Rifles • 1” or less • heavy smoke stains • loose fibers/melted fibers • star-shaped tear surrounded by smoke • 12”-18” • halo of smoke stain • 25”-36” • scattered gunpowder particles • ball powder cartridges can extend to 6’-8’ • > 3’ • bullet wipe • carbon, dirt, lubricant which wipes off surface of bullet Created by C. Ippolito April 2008

12. GSR Patterns Created by C. Ippolito April 2008

13. GSR Patterns • 3” • 9” • 15” • 21” • Greiss test • shows nitrites • Sodium rhodizonate Test • turns lead particles pink then violet Created by C. Ippolito April 2008

14. Primer Residues • Dermal Nitrate Test • paraffin wax treated w/diphenylamine • blue color w/nitrates • Primer Test • looks for: • lead styphate • barium nitrate • antimony sulfate • SEM Testing • Neutron Activation Analysis • Atomic Absorptive Spectrophotometry Created by C. Ippolito April 2008

15. Serial Number Restoration • detects strain in metal crystals • can be “re-etched” • HCl + copper chloride + water for steel Created by C. Ippolito April 2008

16. Firearms, Tool Marks, and Other Impressions Objectives: List procedures for the proper collection and preservation of firearm evidence. Explain how a suspect tool is compared to a tool mark. Explain the forensic significance of class and individual characteristics to the comparison of impressions. List some common field reagents used to enhance bloody footprints. Created by C. Ippolito April 2008

17. Collection & Preservation of Firearms • Safety – unload any ammo • note hammer/safety position • note location of fired/unfired ammo • Revolver • note chamber position • note cartridge/casing in chamber w/position • each round in own box • Automatic • remove magazine – test for prints • Water recovery • ship weapon with water covering weapon Created by C. Ippolito April 2008

18. Collection and Preservation of Ammo • Must save class/individual markings • free bullets by breaking away material • use only plastic tools • scribe with initials • leave trace materials on bullet • paint, fibers, etc. Created by C. Ippolito April 2008

19. Tool Marks • indented impressions class characteristic • all tools show microscopic irregularities from their manufacturing • indented impressions individual characteristics • microscopic irregularities from damage and wear Created by C. Ippolito April 2008

20. Preserving Impressions • photograph • Lifting Impressions in Dust/Dirt • electrostatic lifting device • Casting Impressions • dental stone (gypsum) • Snow Impression Wax Created by C. Ippolito April 2008