Transcript 2 - fingerprints-developing and Lifting

Chapter 15
Fingerprinting
Courtesy of C. Fanning
Crystal Violet
Courtesy of C. Fanning
Courtesy of C. Fanning
Red Fluorescent
Inked
15-1
Prints
•Making prints
Rolling prints
Modus operandi
•Identifying prints
Ridge count
3 types- loop, whorl, arch
Minutiae
•Developing and Lifting prints
Black, white, fluorescent powders
Chemicals-ninhydrin, iodine, silver nitrate, cyanoacrylate
•Other types of prints
15-2
Patent (Visible) Prints
•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.
Courtesy of C. Fanning
Inked
Crystal Violet
Courtesy of C. Fanning
15-3
Plastic Prints
•Plastic prints are ridge impressions left on a soft material,
such as putty, wax, soap, or dust.
•Locating patent or plastic prints at the crime scene normally
presents little problem to the investigator, because these
prints are usually distinct and visible to the eye.
15-4
Latent Prints
•Once the finger touches a surface, body perspiration and/or
oils 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.
15-5
Detecting Prints: Nonabsorbent
•Latent prints deposited on hard and nonabsorbent surfaces
(e.g., glass, mirror, tile, and painted wood) can be developed
by the application of a powder.
15-6
Detecting Prints: Nonabsorbent
•Super Glue® fuming develops latent prints on nonabsorbent
surfaces, such as metals, glass, electrical tape, leather, and
plastic bags.
•Development occurs when fumes from the glue adhere to
the print, usually producing a white latent print.
•Estimated time: 10 minutes
15-7
Detecting Prints: Absorbent
•Prints on absorbent surfaces (e.g., papers, cardboard, and
cloth) generally require treatment with a chemical.
•Examiners use various chemical methods to visualize latent
prints on absorbent surfaces, such as iodine fuming, ninhydrin,
and Physical Developer.
15-8
Detecting Prints: Absorbent
•Silver nitrate (Physical Developer) --reacts with chlorides to
form silver chloride, a material which turns gray when exposed
to light.
15-9
Detecting Prints: Absorbent
•Iodine fuming develops latent prints on absorbent and
nonabsorbent surfaces, such as paper, cloth, glass, and
plastic bags.
Iodine fuming involves heating iodine crystals that cause
vapors which combine with latent prints to make them visible.
Iodine prints are not permanent and will fade, making it
necessary to photograph the prints immediately.
Estimated time: Few minutes
15-10
Place the Object in an Enclosed
Container with Iodine Crystals
Detecting Prints: Absorbent
•Ninhydrin develops latent prints on porous surfaces, such as
paper and clothing.
•It reacts chemically with trace amounts of amino acids present
in latent prints to produce a purple-blue color.
•Estimated time: 24 hours
15-12
Detecting Prints
•Once the latent print has been visualized, it must be
permanently preserved for future comparison and for possible
use as court evidence.
•A photograph must be taken before any further attempts at
preservation are made.
15-13
Lifting 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.
•Then, the tape is placed on a properly labeled card that
provides a good background contrast with the powder.
15-14
Digital Imaging
•Digital imaging is the process by which a picture is converted
into a digital computer file.
•With the help of digital imaging software, fingerprints, which
are often not in perfect condition, can now be enhanced for the
most accurate and comprehensive analysis.
•An important and useful tool, especially for fingerprint
identification, is the compare function that places two images
side by side and allows the examiner to chart the common
features on both images simultaneously.
15-15
AFIS
•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).
15-16
AFIS
•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.
Making your ‘10 Card’
15-17
How Does AFIS Work?
•Fingerprint images are scanned
and digitized
•Minutiae are coded
•Minutiae are searched by
computerized matchers
•Search candidates are produced
side-by-side on a computer screen
•Candidates are examined
Algorithm using Minutiae
Replaces point ID
Faster
Ten Card Print
Uses computers
More accurate
Crime Scene Print
Other Prints
Ears--shape, length and width
Shoes--can be compared and identified by type
of shoe, brand, size and year of purchase
Other Prints
Palm-lines can be
identified and may be
used against suspects.
Other Prints
Foot Prints are taken at birth
as a means of identification
for infants.
Other Prints
Lips--display one of
five common patterns
Short vertical lines
Long vertical lines
Rectangular lines
that may crisscross
Diamond
Branching
Other Prints
Teeth--bite marks are
unique and can be
used to identify
suspects. These
imprints were placed
in gum and could be
matched to crime
scene evidence.
Other Prints
The blood vessel
patterns may be
unique to individuals.
Today they are used
for various security
purposes.
Portfolio
A portfolio is a collection of work that
demonstrates what you know and can do. It
shows your best work. In this unit, you will put
together a portfolio of your work on making and
lifting various prints. You will add to your
portfolio as you work through the labs in class
and put it in to a final form at home. You will be
given both written instructions and an
assessment list.