Ch. 15

1. Ch. 15 FIREARMS, TOOLMARKS, AND IMPRESSIONS

2. CH. 15 – FIREARMS, TOOLMARKS, AND IMPRESSIONS • In 2004 – 29,569 gun deaths in US • Suicides account for 56% & homicides for 40% • Us 4.4 deaths per 100,000 compared to Germany with .45 per 100,000 and .015 per 100,000 in Japan • Forensic analysis is vital in order to solve crimes involving guns • Gunpowder was invented in China in 200 AD eventually leading to the development of modern weapons after the propellant was refined and progress in metallurgy, physics, chemistry, and armaments not to mention the continued need to kill.

3. TYPES OF FIREARMS • Handguns or pistols – designed to be held in one hand, easy to carry & conceal, not as accurate as other firearms, limited to number of bullets that are loaded • Revolver – usually 6 bullets are loaded into a cylinder, reloading is by hand, shells are not ejected when spent • Semiautomatic – holds 5-19 rounds in a magazine/clip, shoots 1 cartridge every time trigger is pulled, ejects the spend cartridge case & reloads automatically • Rifles - shoot more powerful cartridges than handguns, greater range & better accuracy, longer barrel • Shotguns – similar to rifles, shoots packet of shot or spherical pellets, inside of barrel is not rifled • Air guns or BB guns – shoots shot or pellets propelled by pressurized air spring compression or a carbon dioxide cartridge

4. TYPES OF AMMUNITION • Composed of cartridge case, primer, propellant and a projectile & varies based on the weapon • Base of the cartridge contains the primer which is struck by the firing pin of the gun igniting the gunpowder in the cartridge case. Gas is created that pushes the projectile out of the cartridge case, along the barrel, & out of the weapon • Over 300 kinds of ammunition for handguns alone • Various parts/pieces of the ammunition used as evidence in an investigation. • Can be either class or individual

5. BULLETS • Bullets made of lead & covered with brass, copper or steel. • Armor-piercing bullets made from steel or tungsten alloys coated with thin layer of lead or copper/brass to prevent barrel wear • Bullet size is a measure of the diameter & expressed in inches and referred to as “caliber.” • Ex: bullet measures 22/100 of an inch is a .22 caliber bullet • Caliber also corresponds to the inside diameter of the firearm’s barrel or bore • If measured in metric – 9 mm – is approximately same size as a .38 caliber. • Size of a shotgun described by gauge & related to the weight of the lead pellets or shot in the shell. Larger the diameter of a shotgun bore, the smaller the gauge • Single pellet is called a slug.

6. BULLET SHAPES • Bullets come in different shapes, see Fig. 15.7, pg. 443 • Bullets with holes in the cone deform on impact to decrease penetration & cause greater bodily harm. • Flat-nosed lead bullets used for target practice • Weight, dimensions, shape & type of bullet are class evidence

7. Handgun & rifle barrels are rifled to increase the accuracy of shooting • “Rifled” refers to the cylinder being machined to form a grooved spiral inside the barrel to create a spin to the projectile, decreasing wobbling in flight, increase accuracy. • Rifling in the barrel produces “Lands” & “grooves” on a bullet that twists either to the left or to the right • Lands & grooves are class characteristics & used to identify the make & model of a weapon. • Striae or scratches on a bullet created from wear patterns • Scratches resemble barcodes which create a unique kind of “fingerprint” for the bullet • Changes the bullets from class to individual characteristics • Problem: many bullets are too badly deformed or fragmented to be helpful.

8. THE CARTRIDGE • The cartridge consists of the bullet & a case or shell that contains the powder and a primer. • Case made of brass or nickel-clad brass • Propellant is smokeless powder • Combustion products of the chemicals are expelled from the ejection port, leaving behind the presence of lead, barium, antimony letting scientists know a weapon was fired.

9. Cartridge found at a crime scene is both class & individual evidence. • Class evidence includes: • dimension of the shell casing • imprint on the base or head stamp • whether it is rim or centerfire • Individual evidence includes: • impressions on the firing pin when it strikes the primer case • ejection of cartridge being pulled out of the firing chamber by a hooked extractor & thrown clear of the chamber by the ejector.

10. DISTANCE FROM TARGET • Knowing the distance from muzzle to target can aid in the reconstruction of the event. • When a bullet leaves the muzzle of a weapon, unburned particles are carried along, plus combustion products of the propellant, which spreads out over distance • Greiss test will chemically convert the nitrites in gunpowder residue into a colored product • Muzzle very close or pressing against the target causes burns & deposits a lot of soot

11. GUNSHOT RESIDUE • The primer ignites the powder charge, hot gases that propel the bullet from the firing chamber blow out from the ejector port & the muzzle. • Blowback disperses combustion products of the primer back to the shooter’s hand, plus blanketing the area alongside & behind the weapon • Presence of lead, barium, & antimony is indicative that a weapon was fired, but the particles may not necessarily be traceable to the shooter because it is widespread & easily transferred • The term “gunshot residue” (GSR) refers to the ejector particles, combustion residues of the powder & any unburned powder particles.

12. GUNSHOT RESIDUE • Well equipped crime lab will be able to confirm GSR residues from a shooter’s hand using sophisticated & expensive instruments. • Blowback contamination is a problem • Tests done on top of the thumb & forefinger & then compare it to the palm helps in interpretation • No GSR on the palm of a shooter, if palm is sprayed with a specific solution & using a UV light it will show the imprint of the pistol grip. • Color of the fluorescence indicates the type of finish on the metal or pistol grip.

13. GUNSHOT RESIDUE • Bureau of Alcohol, Tobacco, Firearms & Explosives’ National Integrated Ballistic Information Network (NIBIN) maintains a forensic data base containing information on bullets & cartridge casings retrieved from crime scenes & test-fires of guns found at crime scene or on a suspect. • Now contains over 1, 286,5000 pieces of evidence • More than 20,300 hits (matches of evidence with other evidence) have been registered

14. Read in your textbook pages Case 15.1: The Case of People v. Contreras, pgs. 454, 455 & 456. • Discuss with your group the following questions: • What do you think happened • Where was the cartridge case? • Was it ever looked for? • What was Ms. Contreras’ state of mind when she called 911? • Why did she confess, yet not know what she did with the rifle? • Why wasn’t GSR tested around the bullet hole to determine the distance of travel? • Why didn’t the state consider a shot from outside?

15. Read the information at the top of pg. 457 & discuss the following questions? • Do you think a thorough & accurate investigation was conducted? If not, state what you felt was missing or done incorrectly. • After reading the case study, what questions do you still have? • What do you feel about the statement: “Justice & truth may not be synonymous.”

16. TOOLMARKS • Many different tools are used in many different ways in many crimes • Ex: screwdriver used to pry open a door. • Toolmarks are caused when the tool is used against a softer material leaving behind impressions. • Ex: metal screwdriver used against the wood frame of a door

17. TOOLMARKS • Toolmarks can be both class & individual evidence • Class evidence–features of the tool itself – its shape & size • Individual evidence – tool over time becomes worn or damaged acquiring unique markings that will differentiate it from other similar tools

18. TOOLMARKS • Toolmarks associated with a crime are 1st photographed &/or sketched • If the tool is left at the crime scene, it is taken to a lab for further examination • If tool is not left behind, a cast is taken of the mark with either silicone, plaster, or clay material • Next, using the cast, a 3 dimensional replica is made. • Class of tool needs to be identified, so that police know what to look for among the suspects • Recovered tools are compared to the toolmark evidence, hopefully finding unique characteristics to achieve a match

19. IMPRESSIONS: FOOTWEAR MARKS OR SHOEPRINTS • Name at least 3 different mediums where shoeprints could be used as evidence. • Information that footprints can reveal about the crime: • Direction of approach & departure • Point of entry & exit • Mode of entry • Sequence of events that took place • Class & perhaps individual evidence linking suspects to the scene

20. IMPRESSIONS: • Standard method of documenting impression evidence is photography • Oblique-angle viewing can make a difference – see Fig. 15.33 on pg. 461 • Methods of collecting & preserving impressions: • Casting • Electrostatic or adhesive lifting if imprint is on a hard surface • Chemical enhancement – dye on a bloody shoeprint

21. IMPRESSIONS: • Matching shoeprint evidence to a shoe involves class characteristics • Manufacturer, type, model & size • Individual characteristics when footwear outsoles becomes worn & damaged • SoleMate is a commercial database that contains manufacturer, date of market release, image or offset print of the sole & pictorial images of the shoe itself. • Contains over 12,000 sport, work & casual shoes • TreadMark is a database that stores & compares imprints from a crime scene.

22. IMPRESSIONS: • Personal Traits • Footprints can sometimes tell you information about the person. • Ex: length of stride & the way the footprint has dug into the ground can suggest running • Walking gait, the length of stride may be related to the height of the individual.

23. TIRE TREADS • Tread marks in tires are treated similar to footwear marks due to the fact that both are mass produced • Class characteristics include: design, size, type & model • Individual characteristics include: wear and damage causes defects used to individualize the tire

24. TIRE TREADS: • Vehicles are often involved in crimes & many times tire marks are the only way to identify a vehicle. • Impressions left in mud, dirt, dust or imprints left on a smooth surface by a moist or dirty tire can be photographed & collected using the same techniques as those used for footwear. • Vehicles very heavy so tire impressions can also be found on a body

25. TIRE TREADS: • Data bases for tires contain information on tread designs, manufacturer, date of market release, wheelbase (distance from the center of the front wheel hub to the center of the rear wheel) & stance (distance from the centerline of the right tire to the centerline of the left tire) • Any changes to a tire’s tread, like bald spots, cuts, etc., could be seen in a cast impression • Tires containing caked soil or wedged rocks in the tread can provide information on periods of time and is referred to as a “temporary chacteristic.” • Skid marks can be used to reconstruct an accident, hit & run, & tire failures in moving vehicles

26. BITE MARKS: • Bite mark evidence is common with victims of domestic violence & in some case an assault or sexual attack • Everyone’s teeth that are slightly different shapes, widths & arrangement. • Chips, fillings, crowns & caps make a person’s teeth unique. • Odds of 2 people with the same bite marks with a full set of 32 teeth is 2.5 billion to 1. • Bite marks were a prime piece of evidence to convict serial killer Ted Bundy

27. RESTORATION OF SERIAL NUMBERS: • Many items have serial numbers & are assigned so that ownership can be traced • Ex: VIN # on a car • Criminals try to obliterate the identification # - usually by grinding it off

28. RESTORATION OF SERIAL NUMBERS: • Process to create the identification number: • Metal is stamped or punched creating a crystal structure beneath the impression that is deformed • Area will react to an etching solution more readily than the surrounding area • Restoration of identification number: • On metal – 1st polish the area with emery cloth & repeated swabbing with an acidic chloride solution will retrieve the numbers • Retrieving numbers can also be done on wood, plastic & precious metals