Transcript Fingerprints - Little Miami Schools

Types of Crime
Scene Prints
Types of Crime Scene Prints
• Three Types:
Patent Prints
Plastic Prints
Latent (Invisible) Prints
Patent Prints
• Can be seen with the
naked eye
• Made by fingers touching
a surface after ridges
have been in contact with
a colored material such
as blood, paint, grease,
ink, etc.
Plastic Prints
• Can be seen with the naked eye
• Made by ridge impressions left on a
soft material such as putty, wax,
soap, dust, wet painted surfaces,
etc.
Latent (Invisible) Prints
• Latent fingerprints are those that are
not visible to the naked eye. These
prints consist of the natural secretions
of human skin and require development
for them to become visible.
• They are made by impressions caused by
transfer of body perspiration or oils
present on finger ridges to the surface
of an object
Detection of Prints
• Latent prints must be developed
(found) through different methods
• The method used is dependent on
the surface being examined
Surface Conditions
• Hard, nonabsorbent surfaces (glass,
mirrors, tile, painted wood):
Powders or Super Glue Fuming
• Absorbent surfaces (paper,
cardboard, cloth): One or more
specific chemicals
Fingerprint Powders
• Non-absorbent surfaces only
• Applied with a camel’s hair or
fiberglass brush (DO NOT TOUCH)
• Color of powder chosen contrasts with
surface color
• Powder adheres to oils and perspiration
left by ridges
• Print can be lifted off the surface and
preserved
How to Develop
Fingerprints With Black
Powder
•
http://www.youtube.com/watch?v=tqFzVfPRd5s
Fingerprint Powders
• Some investigators use fluorescent powder
and UV lights to help them find latent prints
on multi-colored or dark surfaces.
• Magnetic powder can also be used to reveal
latent prints. This type of powder works better
on shiny surfaces, some paper, or plastic
baggies or containers.
Iodine Fuming
Oldest chemical method for developing
latent prints.
• Iodine is a solid crystal that, when
heated, is transformed into a gas
through sublimation
Iodine Fuming
• Iodine fumes react with oils and
fats to produce a temporary
yellow-brown colored print.
• Iodine prints are not permanent and
must be photographed immediately
or fixed with starch solution, which
can last about 1 month
Ninhydrin
• Chemical used to develop prints on
porous material by reacting with
amino acids in perspiration
• Developed prints appear purple-blue
in color
• Prints appear within an hour or two
and fully developed in 24-48 hours
• Commonly used on paper products
Superglue Fuming
• Used on nonporous surfaces such as
metal, electrical tape, leather, and
plastic bags
• Active ingredient: cyanoacrylate ester
• Evidence is placed in a fuming chamber
and the cyanoacrylate is heated and
covers the object and produces a hard
white latent print
Super Glue Fuming
•
http://www.youtube.com/watch?v=FkcSkADVMIM
Laser Light
• Perspiration contains a variety of
components that fluoresce when
illuminated by laser light
• Because of the fluorescence, latent
prints can be seen with the naked
eye
• Almost never used anymore with the
invention of alternate light source
(ALS) latent print examination
Alternate Light Source (ALS)
• Works because perspiration fluoresces
under different wavelengths of light
• Can adjust the wavelength of light to
be aimed through a fiber optic cable
• More commercially available than laser
light setups
Preservation of Prints
• Common fingerprint methods do not
interfere with further DNA analysis
• However, when biological material
remains, fingerprints should be
developed at the crime lab instead of at
a crime scene
Preservation of Prints
• After prints have been found,
photos must be taken
• If object is small enough to be
transported without destroying the
print, it should be preserved intact
• Cellophane should cover the print to
protect from damage
Preservation of Prints
• Prints on immovable objects should
be lifted
• Lifted prints should be preserved on
a card that provides contrast
Other Prints
Palm - friction
ridges can be
identified and may
be used against
suspects
Kendall/Hunt Publishing Company
21
Other Prints
Footprints are
taken at birth
as a means of
identification
of infants.
Kendall/Hunt
Publishing Company
22
Other Prints
Iris Scan recognition is the
process of recognizing a
person by analyzing the
random pattern of the iris.
The automated method of
iris recognition is relatively
young, existing in patent
since only 1994.
MythBusters & Fingerprints
• http://www.youtube.com/watch?v=MAfAVGESYc&feature=related