Fingerprints

Fingerprints• Made of grooves and friction ridges.

• Fingerprint pattern is left by friction ridges.

• Ridges evolved for efficiency – they are useful in holding things, opening doors etc.

• Are individual and not shared

• Remain unchanged throughout life

• show general patterns so can be classified

• all people share these patterns.

• Classifying Prints• FBI has more than 200 million fingerprints on file.• Basis for fingerprint matching and identification -• Whorls• Loops • Arches

• Everyone has them. • How they have them is unique.• Each person has a different number of these types of

patterns and the pattern varies from fingertip to fingertip on each person.

Arches

• 5% of all pattern types

• Ridgelines rise in center to create wavelike pattern

• Can be plain or tented; tented rise more sharply.

Loops• 60% of patterns

• One or more ridges that double back on themselves

• Can be radial where loops flow down towards radius (thumb side)

• Or can be ulnar, where loops flow towards ulna (little finger side)

Whorls• 35% of patterns• Look like whirlpools of ridgelines• Can be plain – concentric circles like a bulls

eye• Central pocket whorls look like a loop with a

whorl at its end• Double loop whorls – two loops that collide

to produce S shape• Accidental loop whorls are different from

other whorls – irregular.

The Henry System

• Individual prints are assigned scores based on where whorls show up in the 10 fingerprint set; final discrimination of prints is always manual.

AFIS – Automated Fingerprint Identification System

• Computer scans and digitally encodes fingerprints and stores that information.

• Computer can search thousands of files per second, when a match is found agent has to verify them individually.

Types of fingerprints• Patent prints – occur when blood, ink paint, dirt or

grease on fingers are left behind as a visible print• Plastic prints – have a 3-D quality and occur when

there is an impression in wax, putty, caulk, soap, butter or dust

• Latent prints – invisible. They need lighting and luminal to be seen.

• Finding Latent prints – can be found since fingers pick up oils and dirt from skin.

• Latent prints can be powdered and lifted.• Using Cyanoacrylate vapor (Superglue) -

print can then be photographed or treated with a fluorescent dye that bind to print. Other ways use iodine, ninhydrin and silver nitrate

Trace Evidence

• any tiny piece of physical material that can be transferred from one person to another, or between a person and a crime scene.

• Links suspects, places and objects.

• Examples = hair, human or pet, fiber from clothing, paint chips, dust, sand, pollen, seeds.

• HAIR

• Grows from cells in a follicle.

• Hair shaft - 3 parts –medulla, cortex and cuticle.

• (Analogy = pencil; lead = medulla, wood = cortex, cuticle = paint) Cross section of human hair

• Cortex contains pigment - gives hair its color.

• Medulla = central core.Cross section of human hair

• Cuticle covers shaft; looks like scales (analogy = roofing tiles); 3 distinct patterns

Coronal scales – look like stack of paper cups

Photomicrograph to show scale pattern on human hair – imbricate pattern

• Medullary index = width of the medulla compared to the overall width of the hair.

• Most animals’ medullary index is 0.5 or greater.

• In humans the index is about 0.3 (medulla is about 1/3 the width of the hair)Dog Hair Horse Hair Human Hair

• Dyed Hair

• Hair grows about ½ inch a month;

• Un-dyed hair root gives the criminalist plenty of data: can tell if the hair has been bleached, dyed, treated, and when it was last done!

• When comparing the following• color and width• Pattern of the medulla• Color and pattern of pigments• Cuticle pattern

• If a hair matches a person in all 4 aspects then there is a 1 in 4500 chance the hair found at a crime scene came from a suspect.

• Animal hair cuticle has a different scale pattern.

Deer Hair

Bat Hair

Human Hair

• Synthetic fibers have no medulla. Fibers may appear twisted. A cross section of a fiber may appear trilobal under the microscope. Also, fibers may contain delusterants (chemicals added to fiber to get rid of shininess) that will appear as little dots under the microscope.

Ballistics

Types of Bullets• Lead bullets

• Used in low velocity weapons (small handguns, and .22 or .25 caliber rifle)

• Deform and fragment when they hit the target

• Cause severe tissue damage

• Lead alloy bullets

• Harder then lead bullets

• Deform and fragment less when they hit the target

• Penetrate deeper

• Semi jacketed bullets- • Thin layer of brass coats the sides with

soft lead nose exposed• Used in low velocity and high velocity

weapons (.357 and .44 magnum handguns and high powered rifles)

• Slightly hollow nose will deform and fragment and cause a lot of tissue damage when it hits the target

• Fully jacketed bullets-

• Completely covered with brass (full metal jackets)

• Used in high velocity guns (.44 magnum handguns and high powered rifles)

• Greatest penetrating power

Determining Caliber • Caliber = measurement of the internal diameter of the gun

barrel• Rifles and handguns measured in inches or mm (example =

a .38 caliber handgun barrel has an internal diameter of .38 inches)

• If a bullet is intact and not severely deformed its diameter can be measured at the base to determine the caliber of the gun it came from

Shell Casings• Portion of the cartridge that remains after the powder

explodes and the bullet is gone. Retain several important markings:

• Impression left by the firing pin • Knowing where the firing pin struck (center or around the

edge) helps to narrow down the type of gun it came from• Head stamps• Manufacturer’s initials or log, caliber or gauge, and

cartridge types or stamped on shell’s when they’re made• Extractor and Ejector Marks• Made by automatic and semiautomatic weapons that are

unique to each weapon

Bullet Markings: Rifling and Ridges

• Rifling = Spiral grooves etched in to the side of gun barrels to make bullets spin as they are shot (makes bullet more accurate)

• Results in Lands and Grooves (striations) on the bullet

• Lands – High parts between rifling marks (raised part on bullet, tends to be wider)

• Grooves- low part in rifling marks (section that’s been gauged out by gun barrel) contains more pronounced striations

• Bullets shot from the same gun will exhibit the same striation pattern