Firearms toolmarks and Impressions

1. Firearms toolmarks and Impressions

2. Types of Firearms Handguns (pistols) Revolver Semiautomatic Rifles Shotguns Air or BB guns

3. Ammunition Components: Cartridge case Propellant Primer Projectile

4. Bullets Bullet size—diameter (caliber or gauge) Shapes Made of lead, sometimes jacketed with brass, copper, or steel

5. Rifling Lands and grooves are class characteristics. The grooved spirals inside the barrel of a gun that produce lands and grooves on a bullet

6. Striae Scratches on a fired bullet, like a barcode, that can serve as individual evidence, matching bullets or bullet to a firearm

7. Cartridge Case Head stamps Rimfire and centerfire cartridges Usually brass or nickel-clad brass Class evidence

8. Cartridge Case, continued Firing pin marks Individual characteristics Extractor marks Breech marks

9. Features of a Semiautomatic Handgun

10. Firearms Evidence Class: Bullet type Bullet caliber Bullet weight Lands and grooves Rifling Cartridge case Head stamp Individual: Striae Firing pin marks Breech marks Extractor marks Ejector marks Chamber marks

11. Gunshot Residue (GSR) When a weapon is fired: Primer and propellant particles blow back toward the shooter. Combustion products (mostly NO2-), unburned propellant, and particles of lead follow the bullet, spreading out with distance.

12. Distance to Target The Greiss test converts nitrites to an orange-red color. Sodium rhodizonate reacts with traces of lead to make purple spots.

13. Identification Comparison Microscope • The single most important tool for a firearms examiner • Two bullets can be observed and compared simultaneously within the same field of view • Not only must the lands and grooves of the test and evidence bullet have identical widths, but the longitudinal striations on each must be the same

14. Identification (continued) Computerized Imaging • Computerized imaging technology has made it possible to store bullet and cartridge surface characteristics similarly to automated fingerprint files • The National Integrated Ballistics Information Network (NIBIN) produces database files from bullets and cartridge casings retrieved from crime scenes or test fires from retrieved firearms, often linking a specific weapon to multiple crimes • It is important to remember, however, that the ultimate decision for making a final comparison must be determined by the forensic examiner through traditional microscopic methods

15. Toolmarks Tools often used in burglaries may leave a mark. Class characteristics: type, size, shape Individual characteristics: features from wear and damage

16. Lab Activity: Matching Toolmarks ? ? Photography and casting are important to match tool with mark.

17. Tool Marks and Other Impressions Tool Marks A tool mark is any impression, cut, gouge, or abrasion caused by a tool coming into contact with another object A careful examination of the impression can reveal important class characteristics, such as the size and shape of the tool It is the presence of minute imperfections on a tool that imparts individuality to it The shape and pattern of such imperfections are further modified by damage and wear during the life of the tool • The comparison microscope is used to compare crime scene tool marks with test impressions made with the suspect tool • When practical, the entire object or the part of the object bearing the tool mark should be submitted to the crime laboratory for examination • Under no circumstances should the crime scene investigator attempt to fit the suspect tool into the tool mark • Any contact between the tool and the marked surface may alter the mark and will, at the least, raise serious questions about the integrity of the evidence

18. Other Impressions • Abrasion mark – a mark produced when a surface slides across another surface • Cutting mark – a mark produced along the edge as a surface is cut • Indentation mark – a mark or impression made by a tool on a softer surface • Impressions of other kinds, such as shoe, tire, or fabric, may be important evidence • Before any impression is moved or otherwise handled, it must be photographed (including scale) to show all the observable details of the impression • If the impression is on a readily recoverable item, such as glass, paper, or floor tile, the evidence is transported intact to the laboratory

19. Other Impressions (continued) • If the surface cannot be submitted to the laboratory, the investigator may be able to preserve the impression in a manner similar to lifting a fingerprint • When shoe and tire marks are impressed into soft earth at a crime scene, their preservation is best accomplished by photography and casting • In areas where a bloody footwear impression is very faint or where the subject has tracked through blood, leaving a trail of bloody impressions, chemical enhancement can visualize latent or nearly invisible blood impressions

20. Impressions Shoeprints Class characteristics— manufacturer, type, model, size Individual characteristics—wear patterns, nicks, marks, occlusions (like pebbles or sticks)

21. Impressions, continued Shoeprints Captured by oblique-angle photography or chemical enhancement; also by casting in soil, or lifting.

22. Impressions Treated much the same as shoeprints Tire Treads Class characteristics involve design, size, type, and model. Wear and damage cause defects that can lead to individualization.

23. Impressions, continued Bite Marks Result from assault or sexual attack, common in domestic violence Individual evidence, if enough impressions Bite marks were the prime evidence in the conviction of serial killer Ted Bundy.

24. Impressions, continued Serial Numbers Restoration of serial numbers Items of value may have ID numbers stamped into them. Grinding is usually used to obliterate identification numbers. To restore ID numbers on metal, an acid etching solution is employed. HCl-CuCl2

25. Forensics: Debate Both Sides of the Issue; Gun Control Laws Should gun sales and ownership be subject to federal regulation? Introduction Pro/con sides Assertion Evidence Personal opinion MUST BE HANDWRITTEN!!!!