Fingerprints Dermatoglyphics and Dactyloscopy

SFS1. Students will recognize and classify various types of evidence in relation to the definition and scope of Forensic Science. b. Distinguish and categorize physical and trace evidence (e.g. ballistics, drugs, fibers, fingerprints, glass, hair, metal, lip prints, soil, and toxins).SFS2. Students will use various scientific techniques to analyze physical and trace evidence. a. Identify and utilize appropriate techniques used to lift and evaluate readable, latent, plastic and visible fingerprints.

ESSENTIAL QUESTIONS

1. What are the basic principles underlying the forensic use of fingerprints?

2. How can you use minutiae to identify and distinguish prints?

3. How can you use patterns to identify and distinguish prints?

ESSENTIAL QUESTIONS

4. How can you identify and distinguish the three types of transfer prints?

5. What methods are used to detect and visualize specific types of prints?

History

The first systematic attempt at personal identification was devised in 1882 by a French police expert, Alphonse Bertillon.The Bertillon system relied on a detailed

description of the subject, combined with full length and profile photographs and a system of precise body measurements called anthropometry.

History In 1892 Francis Galton published his

classic textbook Finger Prints.At Galton’s insistence, the British government

adopted fingerprinting as a supplement to the Bertillon system.

The next step was the creation of classification systems capable of filing many thousands of prints in a logical and searchable sequence.Sir Edward Henry devised a classification

system between 1896 and 1925.

History In 1903, when the

Bertillon system could not distinguish between two men (Will West and William West), it was fingerprinting that clearly distinguished them.

What is a fingerprint? Fingerprints are a reproduction of epidermal friction

skin ridges found on the palm side of the fingers and thumbs, the palms, and soles of the feet.

During fetal development, friction ridges are formed and are permanent throughout life until death and decomposition.

These friction areas have a series of lines made up of hills (ridges) and valleys (furrows).

These are specialized for traction and enhanced sensory perception.

Fingerprint Principles The basic principles underlying the use of

fingerprints in criminal investigations are that:(1) a fingerprint will remain unchanged during

an individual’s lifetime;(2) fingerprints have general ridge patterns

that permit them to be systematically classified; and

(3) a fingerprint is an individual characteristic because no two fingers have yet been found to possess identical ridge characteristics.

Fingerprints are permanent

The epidermis is the outer layer of the skin, while the dermis is the inner layer of the skin.

The dermal papillae is the layer of cells between the epidermis and dermis, that is responsible for determining the form and pattern of the ridges on the surface of the skin.

Once the dermal papillae develop in the human fetus, the ridge patterns will remain unchanged throughout life except to enlarge during growth. Thus, a fingerprint will remain unchanged during an individual’s lifetime.

Injury can alter a fingerprint, but the damage must extend 1-2mm into the dermis.

Fingerprints have patterns All fingerprints are divided into three

classes on the basis of their general pattern: loops, arches, and whorls.

60% of people have loops35% have whorls5% have arches

A loop must have one or more ridges entering from one side of the print, recurving, and exiting from the same side.

All loops have one core and one delta

Loops

If the loop opens toward the pinky, it is called an ulnar loop (94%).

If the loop opens toward the thumb, it is called a radial loop (6%).

Loops

Whorls Whorls are divided into four groups: plain

(71%), central pocket loop (13%), double loop (13%), and accidental (3%).

■ All whorl patterns have one or more cores and a minimum of two deltas.

Whorls A plain whorl and a

central pocket loop have at least one ridge that makes a complete circuit.

If a line drawn between the two deltas touches the spiral, then it is a plain whorl.

If the line does not touch the spiral, it is a central pocket loop whorl.

Whorls The double loop is

made up of two loops combined into one fingerprint.

An accidental either contains two or more patterns, or is a pattern not covered by the other categories.

Arches Arches, the least common of the three

general patterns, are divided into two distinct groups: plain arches (60%) and tented arches (40%).

Arches do not have type lines, deltas, or cores.

Arches The plain arch is formed

by ridges entering from one side of the print, rising and falling, and exiting on the opposite side (like a wave).

The tented arch is similar to the plain arch except that instead of rising smoothly at the center, there is a sharp upthrust, or spike, or the ridges meet at an angle that is less than 90 degrees.

Henry Classification System Worldwide acceptance in 1899 Allows for up to 1,024 primary groupings

First, the fingers are assigned a value from 1-10 Next, a numerical value is assigned to fingers

that contain a whorl pattern Any fingers containing non-whorl patterns are

assigned the number 0.

Henry Classification System The fingerprint record’s primary grouping

is determined by calculating a ratio:

Henry Classification System If, for example, an individual has a fingerprint

record with a LWAALALWLA pattern series (RT to LP), the corresponding classification ratio would be 19:1

Henry Classification System Approximately 25 percent of the population

falls into the 1/1 category; that is, all their fingers have either loops or arches.

A fingerprint classification system cannot in itself unequivocally identify an individual; it will merely provide the fingerprint examiner with a number of candidates, all of whom have an distinguishable set of prints in the system’s file.

Fingerprints are unique The probability for the existence of two identical

fingerprint patterns in the world’s population is extremely small (1:6,000,000,000)

Besides theoretical calculations, of the millions upon millions of individuals who have had their prints classified, no two fingerprints have been found to be identical.

The individuality of a fingerprint is not determined by its general shape or pattern, but by the careful study of its ridge characteristics, known as minutiae.

Minutiae It is the identity, number, and relative

location of these minutiae that imparts individuality to a fingerprint.

There are as many as 150 minutiae on the average finger, but typically only 35-70 are identifiable.

http://www.dkfz.de/tbi/projects/bmcv/images/iu_it246_04s_fingerprint1.jpg

Minutiae

After a three year study, it was determined that “no valid basis exists for requiring a predetermined minimum number of friction ridge characters which must be present in two impressions in order to establish positive identification.”

In a judicial proceeding, an expert must demonstrate a point-by-point comparison in order to prove the identity of an individual.

AFISAutomated Fingerprint Identification System

The heart of AFIS technology is the ability of a computer to scan and digitally encode fingerprints so that they can be subject to high-speed computer processing.

AFIS aids in classifying and retrieving fingerprints by converting the image of a fingerprint into digital minutiae that contain data showing ridges at their points of termination (ridge endings) and their branching into two ridges (bifurcations).

When the search is complete (a computer can make thousands of comparisons per second), the computer produces a list of file prints that must be examined by a trained fingerprint expert.

Visible Prints

Visible (patent) prints are made when fingers touch a surface after the ridges have been in contact with a colored material such as blood, paint, grease, or ink.

Latent Prints Once the finger touches a surface, body

perspiration, oils and/or proteins present on the finger ridges are transferred to that surface, leaving an impression.

Prints deposited in this manner are invisible to the eye and are commonly referred to as latent or invisible fingerprints.

Plastic Prints

Plastic prints are ridge impressions left on a soft material, such as putty, wax, soap, or dust.

Detecting Prints The best detection technique will depend on

The nature of the surfaceThe presence of contaminantsEnvironmental factorsAge of the prints

There are three categories of techniques that are used: Instrumental/OpticalPhysicalChemical

Instrumental Detection Instrumental detection should always be

done first as they are non-destructive to the print.

These techniques are also useful in that they may significantly improve the results obtained by physical and chemical methods.

Instrumental Detection

RUVIS (Reflected Ultraviolet Imaging System) Can image latent and processed prints by

using intensified UV reflectance instead of fluorescence

Instrumental Detection

MXRF (Micro-X-ray Fluorescence) Can image both visible and latent

fingerprints by detecting the presence of of inorganic elements (Na, K, Cl) in print residue resulting from perspiration

Physical Detection Latent prints deposited on smooth, hard

and nonporous surfaces (e.g. glass, mirror, tile, and painted wood) are preferably developed by the application of a powder

Powders, available in a variety of colors, can be applied with a brush or magnetic wand, and adhere to perspiration and/or body oils of the print

Physical Detection Latent prints deposited on rough, more

flexible, nonporous surfaces (e.g. plastic, vinyl, aluminum foil, leather, tape) are preferably developed by cyanoacrylate (Super Glue ® ) fuming

Print development occurs when fumes from the glue adhere to the print, usually producing a white latent print

Physical Detection Latent prints on porous surfaces (e.g.

paper, cloth, raw wood) can be developed by iodine fuming

Heating iodine crystals produces vapors that combine with print oils to make them visible.

Iodine prints are not permanent and will fade, making it necessary to photograph the prints immediately.

Chemical Detection Ninhydrin is used to develop latent prints

on porous surfaces (primarily paper). Reacts chemically with trace amounts of

amino acids present in print residue to produce a purple-blue color

Prints can be “fixed” by spraying with a zinc chloride solution, changing the print to an orange-brown color

Can detect prints over 50 years old

Chemical Detection

DFO (1,8-diazafluoren-9-one) is similar to ninhydrin in that it is used for primarily paper, and it reacts with the amino acids in print residue

Fluoresces when illuminated with blue-green light (ninhydrin does not)

More sensitive and can develop up to 3x more prints than ninhydrin

Chemical Detection

Physical Developer is similar to other chemical methods in that it is used on porous surfaces

Reacts with lipids in print residue It is a silver nitrate-based reagent used to

develop prints when other chemical methods are ineffective

Can be used on wet samples

Sequence for Latent Print Development

Is the print on a porous or nonporous surface?

If nonporous…is surface smooth or rough? Can it be transported easily?

If smooth – use powders If rough – use cyanoacrylate fuming If easy to transport – use cyanoacrylate fuming

If porous…is surface wet or dry? If wet – use Physical Developer If dry – use iodine fuming DFO ninhydrin PD

Transporting Prints If the object is small enough to be

transported without destroying the print, it should be preserved in its entirety

Prints on large immovable objects that have been developed with a powder can best be preserved by “lifting” with a broad adhesive tape

The tape is placed on a properly labeled card that provides a good background contrast with the powder