Transcript Fingerprint Development.latent prints

DEVELOPMENT OF
LATENT PRINTS
COMPOSITION
OF FINGERPRINTS

Sweat
99.0-99.5 % water
 0.5-1.0% solids

50% organic solids (mostly amino acids)
 50% inorganic solids (NaCl and KCl)

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Contaminants
Bodily fluids (blood, saliva, nasal
secretions, semen, etc.)
 Oils and fats (sebum)
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THREE TYPES OF
FINGERPRINT IMPRESSIONS

Patent fingerprints – visible prints left on a
smooth surface when blood, ink, or some other
liquid comes into contact with the hands and is
then transferred to the surface
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THREE TYPES OF
FINGERPRINT IMPRESSIONS
(CONTINUED)

Plastic fingerprints – actual indentations left
in some soft materials such as clay, putty, wax,
or dust.
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THREE TYPES OF
FINGERPRINT IMPRESSIONS
(CONTINUED)

Latent fingerprints – fingerprints that are
invisible to the naked eye and caused by the
transfer of oils and other bodily secretions onto a
surface. They can be made visible by various
different methods
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FINGERPRINT POWDERS
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Applied lightly to a
nonabsorbent surface
with a soft brush.
They readily adhere to
sweat residues and/or
deposits of body oils left
on the surface.
Investigators need to
prevent damaging the
print when trying to
develop it
Did you know? Camel hair is the most common animal
hair used to make fingerprint brushes. Now many
brushes (like the one above) are made out of fiberglass.
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FINGERPRINT POWDERS
(CONTINUED)
Gray and black powders – the most
common, chosen to make the best contrast
with the surface
 Fluorescent powders – used to
photograph latent prints on multi-colored
surfaces. They fluoresce under ultraviolet
light.

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FINGERPRINT POWDERS

(CONTINUED)
Magnetic powder –
magnetic powders are
applied with a magnetic
brush

Allows for very delicate
application of powders,
decreasing chances of
scratching prints with
bristles
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THINGS TO CONSIDER ABOUT
FINGERPRINT POWDERS…
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Fineness
 The powder must be fine enough to show the detail of the fingerprint.
Finer powders would be theoretically capable of displaying greater
detail than coarser powders.
Adhesion
 The powder must display the right level of adhesion, so that it will
adhere to the residue of the fingerprint (often oils) and not adhere to
the rest of the surface where it would obscure the view of the print.
When a powder coats a surface, this is known as 'painting'.
Sensitivity
 Sensitivity is related to adhesion, and is how well the powder adheres
to a surface. For example, aluminum flake is more sensitive than
aluminum powder, but greater sensitivity is not always desirable.
Color The fingerprint powder must be a suitable color for the surface
in question.
Flow
 To a lesser extent, it is important that the powder can flow, and does
not 'cake' into a solid block, which would render it useless.
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FINGERPRINT CHEMICALS

Ninhydrin – reacts with amino acids in sweat to
form purple-blue prints. A 0.6% solution (in
ethanol) is sprayed onto porous surfaces such as
paper.
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amino acids in fingerprints
R
O
H2N
OH
C
COO
O
O
H
N
OH
O
Ninhydrin
O
O
Ruhemann's Purple Complex
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FINGERPRINT CHEMICALS


(CONTINUED)
Physical Developer – silver nitrate-based liquid reagent
used on porous surfaces. It is often used as the last resort
because it destroys protein.
Cyanoacrylate (superglue) fuming – developed in 1982
by Japanese Police. It is used on a variety of materials not
only to visualize latent prints, but also to semipermanently affix them to the surface. Works best on
nonporous surfaces. Can be developed further with
powders or fluorescent dyes
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FINGERPRINT CHEMICALS
(CONTINUED)
DFO (1,8-diazafluotrn-9-one) –
newer replacement chemical for
ninhydrin. It is 2.5 times more
sensitive than ninhydrin.
 Rhodamine 6G is a fluorescent dye
that may be used after
cyanoacrylate fuming to visualize
latent prints under laser light.
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Once fluorescent dyes are applied,
fingerprints can then be visualized
using an Alternate Light Source
(ALS) in an effort to enhance ridges
and minimize background
interference
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FINGERPRINT CHEMICALS

(CONTINUED)
Iodine fuming – one of the oldest latent print
development methods. Solid iodine crystals
sublimate and the vapor will react with fatty oils
and some sweat residue. Iodine prints are not
permanent and will begin to fade once the fuming
process is stopped. Can be used on porous and
nonporous surfaces
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FINGERPRINT CHEMICALS
(CONTINUED)
Gentian violet (or crystal
violet) – used for developing
latent prints on the adhesive side
of tape. An aqueous solution of
crystal violet is sprayed directly
onto the adhesive.
 Wetwop is another solution
developer that can be used on
adhesive surfaces.
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FINGERPRINT CHEMICALS
(CONTINUED)

Amido Black – protein dye stain that can
develop faint bloody fingerprints on porous and
nonporous surfaces. Blood must be swabbed
prior to amido black application for any DNA
analysis
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FINGERPRINT CHEMICALS

(CONTINUED)
LCV (Leuco Crystal Violet) – a protein stain
spray that can develop faint or invisible bloody
fingerprints on non-porous surfaces
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LUMINOL
A chemical that reacts with hemoglobin to
produce the phenomenon of chemiluminescence
(same as fireflies!)
 Can be sprayed where nothing is visible. Under
UV light, blood or bodily fluids glow
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OTHER CHEMICAL
DEVELOPERS…
Sticky-side powder – paste made with powder
that is used after cyanoacrylate fuming and on
the sticky side of tape
 Basic Yellow 40 – another fluorescent technique
for nonporous surfaces or post-cyanoacrylate
fuming
 DAB – Diaminobenzidine formula – another
blood enhancement technique
 Small particle reagent – useful on wet surfaces
such as plastic bags or coated surfaces – adheres
to the fatty deposits in fingerprints
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PRESERVATION OF
DEVELOPED LATENT PRINTS
Photograph!!
 Covering the print to preserve it in its entirety (if
on a small object)
 Lifting the prints with adhesive tape and placing
the tape with prints on a card with labels
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FACTORS AFFECTING
FINGERPRINTS
Age – thinner epidermis, flattening of dermal
papillae, creases, etc.
 Fine ridge structure – less skin contact leads
to a spotty appearance.
 Stimuli – sweating can be due to warmth,
exertion, fever, drugs, anxiety, tension, pain, or
spicy foods.
 Occupational and medical condition –
teaching, and other positions in which a person
handles or shuffles papers, can cause fine ridge
structure.
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FACTORS AFFECTING
FINGERPRINTS
(CONTINUED)
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Transposal factors
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Receiving surface texture
Contaminants on the hands
Contaminants on the receiving
surface
The manner of contact
The amount of pressure
Environmental factors
Temperature
 Humidity
 Handling
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TRENDS WITH FINGERPRINTS
It is NOT possible to determine the age, sex or
race of an individual solely from their
fingerprints. However:
 Statistically in young adults, friction ridges of
women are significantly finer than those of men.
 Fine ridges may be found in the very young and
the very old.
 Manual labor tends to strengthen ridges.
 Women tend to perspire at a lower rate than
men.
 Sodium chloride (NaCl) is lower for women.
 Creases are more common in women's FPs.
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AFIS
Database of fingerprints taken from arrests
and unknown fingerprints found at
unsolved crime scenes
 Investigators enter both known and
unknown prints and identify the minutiae
 When an unknown print is entered into
AFIS, the minutiae are identified and the
computer crosses them with known
offenders
 THE INVESTIGATOR MAKES THE LAST
DECISION on a match
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RESOURCES
UNT in partnership with TEA, Copyright ©. All rights
reserved
 Saferstein, Richard. Forensic Science: An Introduction.
New Jersey: Pearson Prentice Hall, 2008.
 Bertino, Anthony J. Forensic Science: Fundamentals and
Investigations. Mason, OH: South-Western Cengage
Learning, 2009.
 Fisher, Barry A.J. Techniques of Crime Scene
Investigation. 7th ed. Boca Raton, FL: CRC Press,
2004.
 Federal Bureau of Investigations
http://www.fbi.gov/hq/lab/fsc/backissu/jan2001/lpu.pdf
 Investigation Discovery
http://investigation.discovery.com/videos/forensicsvideos/
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VIDEOS
AFIS
http://www.youtube.com/watch?v=ZKi1CKTRCQM
&feature=related
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SUPERGLUE FUMING
http://www.youtube.com/watch?v=FkcSkADVMIM
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Gentian Violet
http://www.youtube.com/watch?v=vBYYrwo8I6s
Ninhydrin
http://www.youtube.com/watch?v=fF_v-MymoOk
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