Forensics Fingerprints

What is the current theory about fingerprints?

• no two people have the same fingerprint

Why do we have ridges on our fingertips?

to help us hold things

What does the imprint of a fingerprint contain?

• natural secretions of sweat glands that are present in the friction ridges of the skin

Categories of fingerprints?

• loops, whorls, arches

core

the center of a loop or whorl

delta

triangular region near a loop

ridge count

• counting from the core to the edge of the delta

What are the types of whorls?

• normal, central pocket, double loop, and accidental

Types of arches

• plain, tented (rises sharply in middle)

Population percentages of fingerprint types

• 65% - loop

• 30%- whorl

• 5% arches

Do fingerprints change?

• no

• unless there is an injury

How are fingerprints determined?

• by minutiae patterns

• also called ridge characteristics

How many minutiae patterns do there need to be before a match is declared?

• not a set number

• generally 8-16

Patent fingerprints

• made by finger touching a surface after the ridges have been in contact with a colored material

plastic prints

• impressions

• ridge impressions left on a soft material (wax, sap, dust)

Latent Prints

• invisible prints left behind by clear oils on the fingertips

Reflected Ultraviolet Imaging System (RUVIS)

• can locate prints on most non-absorbent surfaces without chemicals

• detects latent fingerprints

Fingerprint powders

• can be used for latent Prints

• various colors

• applied with brushes

What are other methods for collecting fingerprints?

• iodine fuming

• ninhydrin fuming

• super glue fuming

Automated Fingerprint Identification System (AFIS)

• contains millions of fingerprint records

• can determine the degree of correlation between prints at a crime scene within prints in the database

How does super glue fuming work?

• having a strong attraction to amino acids, fatty acids, and proteins in a fingerprint

• vapors of super glue adhere to these components

When do you use super glue fuming?

• on uneven surfaces that are hard to dust

• bottles, knives, guns, dead bodies

How does ninhydrin work?

• reacts with amino acids found in our skin (the oil)

• produces a purple product

When is ninhydrin used?

• on porous surfaces

• cloth,paper, cardboard