Download - Forensics ch 4 notes
Fingerprints
Chapter 4
Notes
Mrs. Morgan
A Quick Preview
Recording and classifying prints
• Rolling inked prints
• Loops, whorls, arches, minutiae
• Primary identification number
Lifting prints
• Black, white, and fluorescent powder
• Chemicals—ninhydrin, iodine, silver nitrate, cyanoacrylate
Other types of prints
• Palm, lip, teeth, eye, ear, voice, shoeprints, and footprints
A Brief History…Dactyloscopy
The Study of Fingerprints
History from 1850 to 1900
William Herschel—required Indians to put their fingerprints on contracts, and used fingerprints as a means of identifying prisoners
Henry Faulds—claimed that fingerprints did not change over time and that they could be classified for identification
Alphonse Bertillon—proposed body measurements as a means of identification; termed anthropometry
Francis Galton—developed a primary classification scheme based on loops, arches, and whorls
Edward Richard Henry—in collaboration with Galton, instituted a numerical classification system
The Fundamental Principles
Fingerprint are individual
characteristics.
A fingerprint remains unchanged
during an individual’s lifetime.
Formed during fetal development –
genetic & movement formed
Fingerprints have characteristic ridge
patterns that permit them to be
systematically classified.
Ridge Characteristics
Minutiae
Characteristics
ofridge patterns
Fingerprint Minutiae
Fingerprint Patterns
All friction ridges are divided into 3 classes by their general pattern
Loops 60 %
Whorls 35 %
Arches 5 %
Loopsone or more ridges which enter from one side of the print and exit on the same side
• Area surrounding the loop are 2
diverging ridges called type lines
• Delta: a ridge point nearest the
type line divergence.
• All loops must have at least 1
delta.
Ulnar Loops
opens towards the little finger
Ridges enter and exit from the same side
Delta and type lines
Radial Loops
opens toward the
thumb
Ridges enter and exit from the same side
Delta and type lines
Whorls
• Must have 2 type lines and 2 deltas
• Divided into 4 groups
• Plain whorl
• Central pocket whorl
• Double loop whorl
• Accidental whorl
Plain Whorlmust have at least 1 ridge that makes a
complete circuit around the fingerprint
Deltas and type lines
At least 1 ridge which goes all the way
around
Central Pocket Whorls
At least 1 ridge that goes all the
way around inside of a loop
Deltas and type lines
Whorl
Loop
Double Loop Whorl2 loops within the same point (2 deltas so it is considered a whorl)
Deltas and type lines
Loops
Accidental Whorlsany combination of patterns not
covered by the other groups
Deltas and type lines
whorlloop
Plain Archridges enter 1 side and exit from
the opposite side
Ridges enter and exit from opposite sides
No deltas
Tented Archsharp peak at the center
of the arch
Ridges enter and exit from opposite sides
Sharp peak at center
Fingerprint Classification
Primary Classification
The Henry-FBI Classification System
Each finger is given a point value.
Primary Classification
Assign the number of points for each finger that
has a whorl and substitute into the equation:
right right left left left index ring thumb middle little + 1
right right right left left thumb middle little index ring + 1
That number is your primary classification number.
=
Comparing Fingerprints• Minutiae are identified in the print
and compared to minutiae in
other, known prints.
• There are no legal requirements
in the United States on the
number of points required for a
match. Generally, criminal courts
will accept 8 to 12 points of
similarity.
• The more points that match, the
more confident an analyst can
be.
Kickin’ it Old School
• Fingerprint analysts would manually compare an evidence print to known prints
• Known prints would be cataloged by classification in large books
IAFIS
Established in the 1970s, AFIS
enables law enforcement
officials to:
• Search large files for a set of
prints taken from an individual
• Compare a single print, usually a
latent print developed from a
crime scene
Integrated Automated Fingerprint Identification System
Processing and Recovering
Prints
• Prints should be the 1st physical evidence recovered from a crime scene
• All prints must be photographed before they are disturbed or moved
• Processing of prints depends on the nature of the print
• 3 types of prints exist
Plastic: 3-D impression into a substance such as wax, soap, putty or dust
3 Types of Prints
Visible: left by fingers coated with a colored substance like blood, grease, paint, dirt and ink
Latent: lie hidden or are relatively invisible. Need processing or developing to see
Composition
Prints made of perspiration composed of moisture, sodium
chloride (salt), amino acids, organic/inorganic substances,
and dead skin cell
• How a print is developed depends on the material or surface the print is left in.
• Easily destroyed – do not touch or smear
• Always wear gloves
Tools
• Flashlight
• Magnifying glass
• Alternate light source (UV, colored filter)
• Laser detection system
• Powders
• Brushes
• Tape
• Additional materials
Developing Latent Prints
• Need a substance that interacts with secretions, causing the print to stand out against its background.
• May need to use multiple techniques, done in a particular order so as not to destroy the print.
Most commonPowders—adhere to moisture and
come in many colors and type
Iodine
fumes react with oils and fats to produce a
temporary yellow-brown color.
Developing Latent Prints
Ninhydrin
reacts with amino acids to
produce a purple color.
Developing Latent Prints
Cyanoacrylate
“superglue” fumes react with
water and other fingerprint
constituents to form a hard,
whitish deposit.
Developing Latent Prints
Silver nitrate
reacts with chloride to form silver
chloride, a material that turns gray
when exposed to light.
Developing Latent Prints
More than fingers
Voice
electronic pulses
measured on a
spectrograph
Foot
size of foot and
toes; friction ridges
on the foot
Shoes
can be compared and identified
by type of shoe, brand, size, year
of purchase, and wear pattern
Lips
several common
patterns
Weird Prints
A man has been convicted of suffocating an elderly woman on
the basis of earprint evidence. The assailant was caught after police
matched the imprint of his ear on the victim’s window. Police believe
that the thief put his ear to the window to listen for signs of
anyone home.
Earprint catches murderer