Transcript Methods of Detecting Fingerprintsx

Methods of Detecting
Fingerprints
2 Types of Crime-Scene Prints
• 1. Visible Print- A fingerprint made when the
finger deposits a visible material such as ink,
dirt, or blood onto a surface.
• 2. Plastic Print- A fingerprint impression in a
soft surface.
– Ex: Putty, Wax, Soap, or Dust
Locating Fingerprints
• Visible Prints: This job is easy for the
investigators.
• Latent Prints- (invisible prints)
– Much harder
– Requires the use of techniques to make the print
visible
– Type of surface the print is located on determines
what technique is used
Latent Print Retrieval
• Hard & Nonabsorbent Surfaces: Such as Glass,
mirror, tile, & painted wood
– Prints are developed by the application of powder
or treatment with Super Glue.
• Soft and Porous Surfaces: such as papers,
cardboard, and cloth.
– Require treatment with 1 or more chemicals
Dusting for Prints
Developing Latent Prints
• 1. Fingerprint Powders- These powders stick
to perspiration residue & body oils left on a
surface.
– Should use a fiberglass or camel’s hair brush
– Pick a color that contrasts with the surface
– Fluorescent powders are also used and they show
up under a UV light.
• 2. Iodine Fuming- A technique for visualizing
latent fingerprints by exposing them to iodine
vapors.
• Oldest chemical method used
• Iodine is a solid crystal that when heated is
transformed into a vapor without passing
through a liquid stage.
– Sublimation: A physical change from the solid
directly into the gaseous state.
• As the solid crystals are heated the vapors
combine with parts of the latent print to make
it visible.
• These prints are not permanent and will begin
to fade once the process has stopped.
– Examiner should photograph the prints
– Can also apply a 1% solution of starch in water &
the print turns blue and lasts for several weeksmonths.
• 3. Ninhydrin: A chemical reagent used to
develop latent fingerprints on porous
materials by reacting with amino acids in
perspiration.
• Sprayed onto the porous surface from an
aerosol can.
– Prepared by mixing the ninhydrin powder w/ a
solvent such as acetone.
– Forms a purple/blue color when reacting with
amino acids present in trace amounts of
perspiration.
• 4. Physical Developer- a silver nitrate- based
reagent formulated to develop latent
fingerprints on porous surfaces.
• Very effective on porous surfaces that may
have been wet at one time
• Silver-nitrate reacts with salt deposits in sweat
• 5. Super Glue Fuming- A technique for
visualizing latent fingerprints on nonporous
surfaces by exposing them to cyanoacrylate
vapors; named for the commercial product
Super Glue.
• Develops latent prints on surface such as
metal, electrical tape, leather, & plastic bags
• Super Glue is 98-99% cyanoacrylate ester
– The chemical that interacts with & visualizes a
latent fingerprint.
Watch the video and then answer the questions.
Video Link: http://www.youtube.com/watch?v=FkcSkADVMIM
Courtesy of The Science Spot
• 1. What is the name of the activator used during the process?
A. Hot Prints
B. Hot Stuff
C. Hot Shot
• 2. During fuming the super glue heats up and attaches to _____ _____
in the fingerprint.
A. Skin
B. Amino Acids
C. Valleys
• 3. The evidence is placed in a super glue _____ to develop the prints.
A. Chamber
B. Tube
C. Slide
• 4. What color is the fingerprint after it develops?
A. Red
B. White
C. Yellow
references
• http://www.drakeinvestigations.com/Portals/
56/Fingerprints%20for%20Forensic%20Sectio
n.jpg