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What are Fingerprints?

If a finger touches a surface, perspiration and oils from the body are transferred onto the surface, leaving an impression of the finger’s friction ridge patterns.

Fingerprints may contain traces of any material found in perspiration including DNA and chemicals such as nicotine.

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What are Fingerprints?

Friction ridges are found on skin in the following regions:

Palms of hands
Palmar aspect (palm-side) of fingers
Soles of feet
Solar aspect (sole-side) of toes

They exist to give firmer grip and resistance to slippage.

The number of ridges and their shape is largely determined by genes.

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Skin Surface

Outer surface layer of skin is the epidermis.

The inner layer of skin is the dermis.

Between these two are the dermal papillae.

The papillary pattern determines the form and pattern of the friction ridges on skin surface.

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Skin Surface

Each skin ridge is populated by a single row of pores that are openings for ducts leading from the sweat glands.

Perspiration is released and deposited on the surface of the skin through these pores.

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Fingerprints are Unique

Dermatoglyphics is the study of fingerprints.

No two fingers have yet been found to have identical ridge characteristics (minutiae).

Ridge pattern remains unchanged throughout life.

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Fingerprints do not Change

Friction ridge pattern of skin develops in utero (before birth) due to uneven stresses in the different layers of the developing skin.

Identical (monozygous) twins

have the same DNA.
have different fingerprints.

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Intentionally Altering Fingerprints

Very difficult to do, but there has never been a lack of trying.

Bank robber John Dillinger attempted to burn off his fingerprints with corrosive acid. They grew back.

Illegal immigrants and criminals sometimes undergo finger print plastic surgery. They can still be identified by palm prints and DNA.

To change the pattern requires obliteration of the dermal papillae (1- 2 mm deep).

Attempts to destroy the pattern can backfire and cause more unique details!

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Types of Fingerprint Patterns

There are 3 basic fingerprint patterns

loops

(60-65% of population)

whorls

(30-35%)

arches

(5%)

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Loops

Have ridges entering from one side of the print, turning, and leaving from the same side.

The pattern area of the loop is surrounded by two diverging ridges known as type lines.

The approximate center is called the core.

The ridge point nearest the type line divergence is known as the delta (capital greek letter Δ).

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Loops

65% of the population have loops.

All loops must have one delta.

If the loop opens toward the little finger then it is a ulnar loop.

If the loop opens towards the thumb then it is a radial loop.

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Arches

In an arch, ridges enter from one side of the print and exit on the opposite side.

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Arches

Arches are divided into two distinct groups:

plain arches
tetrarches or tented arches

The tetrarch consists of an upthrusted ridge in the center of the arch.

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Whorls

All whorl patterns must have a core and at least two deltas

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Special Loops

The double loop is made up of two loops combined into one fingerprint.

The pocked loop has a small circle at the core.

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Other Patterns

An accidental pattern contains two or more patterns, but not the plain arch, and is not covered by other categories.

It may consist of a combination loop and plain whorl or loop and tented arch.

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Types of Prints

Latent: hidden or invisible

Made by natural body secretions of the hands and fingers (perspiration & grease)
Requires dusting or other method to make visible

Patent: visible to the naked eye

Blood, ink, dirt, glass

Plastic: a 3-D fingerprint

Wet paint
Soft material like clay

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Impressions and Prints

Impression

3-D
in soft surface
often visible

Print

2-D
transfer of skin perspiration, oils, or a foreign substance
usually latent

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Powder Techniques

Used on non-absorbent surfaces

Tipped or very softly brushed on

Various types

Black powder (carbon)

Grey powder (Aluminum dust)

Magnetic-Sensitive Powder (Magnabrush)

Fluorescent Powder (seen in UV light)

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Classification Systems

Once fingerprints are recorded, a system is required to describe and place them in logical order.

The most prominent system used before computer analysis was the Henry System created by Sir Edward Richard Henry and Azizul Haque in the late 19^th century.

The Henry System is still included as part of many electronic systems and taught by the FBI.

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Henry Classification System

The fingerprint records in this system are classified by broad characteristics.

This system reduces the effort needed to search through vast fingerprint collections.

All 10 fingers are put into groups of 2 with numerical weights assigned to each group

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Henry Classification System

	R Thumb	R Index	R Middle	R Ring	R Pinky	L Thumb	L Index	L Middle	L Ring	L Pinky
Number	1	2	3	4	5	6	7	8	9	10
Value if whorl is present	16	16	8	8	4	4	2	2	1	1

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Henry Classification System

Each fingerprint is then analyzed.

If a whorl is present the value is recorded for that fingerprint.

If a whorl does not exist then zero is recorded for that fingerprint

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Henry Classification System

	R Thumb	R Index	R Middle	R Ring	R Pinky	L Thumb	L Index	L Middle	L Ring	L Pinky
Number	1	2	3	4	5	6	7	8	9	10
Value if whorl is present	16	16	8	8	4	4	2	2	1	1
Example	No 0	Yes 16	No 0	Yes 8	No 0	No 0	Yes 2	No 0	No 0	Yes 1

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Henry Classification System

Next, the Henry Classification Formula is used to find the grouping ratio.

The grouping ratio is a unique identifier for categorizing the particular type of fingerprint that the person has.

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Henry Classification System

The Henry Classification Formula is:

The grouping ratio cannot be simplified. For example, 32/32 and 1/1 are both unique ratios.

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Henry Classification System

	R Thumb	R Index	R Middle	R Ring	R Pinky	L Thumb	L Index	L Middle	L Ring	L Pinky
Number	1	2	3	4	5	6	7	8	9	10
Value if whorl is present	16	16	8	8	4	4	2	2	1	1
Example	No 0	Yes 16	No 0	Yes 8	No 0	No 0	Yes 2	No 0	No 0	Yes 1

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Fingerprint Points

The individuality of a fingerprint is determined by a careful study of its ridge characteristics (points).

Specific traits found in friction ridges are used to establish an identification by their relative location to each other.

The average finger has between 75 and 175 points of identification.

The palmar area has over 2000 points of identification.

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Types of Points

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Matching Points

For two points to match they must be at the same location on the fingerprint be the same type.

At crime scenes only partial prints are usually recovered, therefore a small number of ridge characteristics may be compared.

16 matching characteristics have been suggested to establish the uniqueness of a print.

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Fingerprint Records

Originally, fingerprint records were made with ink on paper cards.

Finger prints were rolled in ink and 4-finger and 2-thumb flat impressions were collected.

Cards can be scanned into modern databases.

The demand for improved systems and digital records has created a movement toward scanning to replace ink.

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IAFIS

Integrated Automated Fingerprint Identification system (IAFIS) is used by the FBI to store digital prints.

It is the largest biometric database in the world, containing records for more than 100 million people.�
When the automated process is finished the system generates a “hit” list

Possible matches then checked by expert
New original prints obtained for checking

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What is included in IAFIS?

Each record may include:

Criminal history
Fingerprints
Mug shots
Scars and tattoos
Physical characteristics

height, weight, aliases, hair and eye color, race

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Who submits data to IAFIS?

The system includes civil fingerprints, mostly of individuals who have served or are serving in the U.S. military or have been or are employed by the federal government.

The fingerprints and criminal history information are submitted voluntarily by state, local, and federal law enforcement agencies.

Employment background checks, some firearms purchases, and the US-VISIT program also provide information to the system.

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