Fingerprints test

fingerprint

an impression of the friction ridges found on the inner surface of a finger or a thumb 

epidermis

Outer layer; Contains melanin; Generates new skin cells that push outward

dermis

Middle layer

-Collagen (protein),elastic tissue, reticular fibers (supportive meshwork of tissue), muscle

Subcutaneous (hypodermis)

Lowest layer; Composed mostly of fat & connective tissue

-An injury must penetrate the dermal layer to alter a print.

When do friction ridges develop?

During the 3^rd and 5^th month of prenatal development.

What do friction ridges do?

They increase the surface area of the fingertip and hands to assist in gripping items.

Aka they give grip/friction to fingertips

They are unique and never repeated

Ridges

The raised portion of skin that comes in contact with ink.

Furrows

The indented portion of skin that does not contact ink

Why can’t a fingerprint be altered easily?

An injury to the skin would have to be deep enough to alter the dermal papillae layer of skin.

This is between the epidermis & dermal layers of skin

Arches

*Ridges enter & exit from opposite sides.

*Found on approx. 5% of the population

*No deltas, no core

Loop

*Ridge enters & exits from the same side

*Found in 60-70% of the population

*1 Delta & 1 Core

*Classified as radial or ulna, depending on which direction it opens towards.

Whorl

*Completes a 360^o pattern

*Found in 25-30% of population

*2 Deltas, 1 Core

*Many forms

Detail Level 1

Type of print

*Loop, arch, whorl & subdivisions

Detail Level 2

Individual minutiae / friction patterns.

*Minutiae patterns

Detail Level 3

Detail of ridge measurements

*Distance between ridges & minutiae patterns.

Radial Loop

Opening of the loop opens towards the thumb.

Ulna Loop

Opening of the loop opens towards the little finger.

Ridge count

The number of ridges crossed between a delta and the core of the pattern.

*Can only be done on loops & whorls.

*Whorls will have a right ridge count & a left ridge count.

IAFIS

Integrated Automated Fingerprint Identification System

*Maintained by the FBI

*Largest database in the world

*Also used for background checks for employment, firearm purchases & identifying remains

NGI

Next Generation Identification

*different from IAFIS b/c they Includes eye-scans, and facial imaging methods

Visible Prints

Left when ridges have a colored substance on them (blood, dirt, paint, grease).

Latent

Impressions caused by perspiration / oils on ridges.

Plastic prints

Impression left in a soft material like

wax, dried/sticky blood, clay, wet paint

Powder

Adheres to body oils, perspiration.

-nonporous & physical treatment

-Color used depends on background.

-Lift with tape, place on card.

Print card contains information regarding the print - crime scene identified, date, time, evidence ID, etc.

Superglue fuming

Fumes adhere to the print and make it white.

-nonporous & physical treatment

-Cyanoacrylate ester is the chemical that interacts with the print.

-Superglue is heated to produce a vapor.

-Can be used on small objects or cover a large area (car interior)

Ninhydrin

Chemical treatment; reacts with amino acids in perspiration.

-porous & chemical treatment

-Sprayed onto surface; 1-2 hours to develop.

-Produces purple-blue print

-Last for 24-48 hours; Photograph!

Iodine fuming

Iodine fumes combine with fatty oils / water

-porous & chemical treatment

-Iodine sublimes (solid to gas)

-Not a permanent image

Silver nitrate

Solution reacts with salt in the print but washes away any trace of protein left on print.

-porous & chemical treatment

-Last resort for developers

- May detect prints on porous objects that may have been wet at one point.

Order of chemical treatment

1) Iodine fuming

2) Ninhydrin

3) Silver nitrate

Alternate Light Source (ALS)

Specific wavelengths of light aimed at a print; based off of fluorescent tendencies of chemically treated prints. (Previously done with lasers)

-Cheaper than lasers

-Portable, easy to use

-Used with chemical treatments

Reflected UV Imaging System (RUVIS)

UV light strikes print and reflects back to a viewer that is converts it to visible light.

-used on nonabsorbant surfaces

Developing fingerprints depends on…

1)surface the print is on

*absorbent, nonabsorbent

2)methods found success my developer

Digital Imaging

Computer programs used to enhance photos of prints

*Filters used to make print clearer (Grayscale, contrast, interference)

*Colors can be differentiated (print on a dollar bill or colored background)

*Compares function – side-by-side comparison.

Flexion creases

Places where the skin flexes/folds causing breaks in the ridge patterns.

-Distal Transverse Crease (distanced from the body)

-Proximal Transverse Crease

-Radial Transverse Crease (closer to the radius bone)