Transcript What is a Fingerprint?

What is a Fingerprint?
A Fingerprint is:
• A deposit of:
– 98% perspiration
– 1% amino acids
– 1% oils
• Formed on the friction ridges of fingers,
palms & feet
• These materials are left on the surface
contacted
Inorganic Constituents of
fingerprint residue from sweat
• Major Components
Na+
K+
Ca2+
Fe2+
ClFBrI-
HCO3PO43SO42NH4OH
Inorganic Constituents of
fingerprint residue from sweat
Minor Components
Mg2+
Zn2+
Cu2+
Co2+
Pb2+
Mn2+
Organic Constituents of
fingerprint residue from sweat
Proteins
Amino Acids
Lipids
Glucose
Lactate
Urea
Pyruvate
Creatine
Creatinine
Glycogen
Uric Acid
Vitamin Sterols
Skin Cross Section
Types of Fingerprints Left at the
Crime Scene
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Latent print impressions
Patent print impressions
Plastic print impressions
Katent print impressions
Patent Print
• Readily visible to the naked eye
• Usually the result of some substance
coating the ridge detail and then allows the
transfer transfer of ridge detail to a surface
that is touched.
• More common substances at a crime scene:
– Blood, paint, grease
• Photograph to preserve as evidence
Plastic Prints
• Visible print to the naked eye where the
print detail is usually in a soft surface
• More common surfaces/substances seen at a
crime scene:
– Window putty, dust, dirt, mud
• Photograph to preserve as evidence
Katent Prints
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Prints made by pre-puberty children
Minutia more compact than adult
Not made by sweat remnants
Easy to lose on objects because mainly
composed of water
Latent Prints
• Prints not visible to the naked eye
• Prints need to be made visible
– through:powders, chemical processes, or lasers
• Most common type of impressions left at
crime scenes.
Non-destructive Methods of Lifting
Prints
• Visual exams
• Alternate light source (ALS)
• Photography
Destructive Methods of Lifting
Prints
• Physical Means (better for non-porous):
– Conventional Powders, Magnetic Powders, Fluorescent
Powders
• Chemical Means (better for porous materials):
– Ninhydrin, Silver nitrate, Superglue (Cyanoacrylate
ester), Iodine fuming, Physical Developer (PD), 1,8diazafluorenone (DFO)
What to include on lift card
• At a minimum include:
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Case #
Date
Print #/letter
Initials of lifting technician
Practice lifting using
conventional powder after being
shown the technique using a slide
Practice lifting using magnetic
powder after being shown the
technique using a slide
Chemical Lifting Techniques
Use with porous objects
Iodine
• Not really a chemical reaction
• Temporary
1. Place a few crystals in closed container
with object.
2. Iodine sublimates
3. Photograph print to preserve it
AgNO3(aq)
1. Cover area with solution (we will use a
brush)
2. Expose area to high energy (e.g. UV) light
source (be careful not to overexpose print)
3. Photograph to help preserve
• AgNO3(aq) reacts w/ salts that are present
AgNO3(aq) + Cl-  AgCl- + UV  2AgCl
2Ag0 +Cl20
Ninhydrin
• Ninhydrin dissolved in alcohol (ethyl,
isopropyl, methyl, or butyl alcohol)
• Reacts w/ amino acids in print (forms
Ruhemann Purple)
1. Place object in solution (or spray solution on
large object, wear protection) to soak
2. Allow object to dry (warm & humid area best)
3. Iron object with steam setting (introduces
warmth & humidity)
Ninhydrin reaction
Ruhemann Purple
Sample results for Ninhydrin
2 more photographic processes
1. 1-8, diazafluoren-9-one (DFO)
2. Physical Developer (PD)
• Both react with salts that are left in the
prints
• Used more often than AgNO3(aq) but similar
processes
Gentian violet (crystal violet)
• Stains fats/oils left behind
• To make solution- .02g/80mL dH2O
• Used for finding prints on “sticky” side of
tape
1. Place tape piece in solution
2. Rinse tape with water
3. Photograph prints that are present
Super Glue (Cyanoacrylic Esters)
• Uses polymerization
• Developed prints appear white
• Heat process:
– Place control print in developing area
– Place 2-3 drops/gal of container on dish
– Heat (we will use coffee warmer)
• NaOH method:
– Place control print in developing area
– Place ~10 drops on cotton ball containing
NaOH