What is a Fingerprint

1
What is a Fingerprint?
2
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

3
Inorganic Constituents of fingerprint residue
from sweat

• Major Components
• Na
• K
• Ca2
• Fe2
• Cl-
• F-
• Br-
• I-

• HCO3-
• PO43-
• SO42-
• NH4OH

4
Inorganic Constituents of fingerprint residue
from sweat

• Minor Components
• Mg2
• Zn2
• Cu2
• Co2
• Pb2
• Mn2

5
Organic Constituents of fingerprint residue from
sweat

• Proteins
• Amino Acids
• Lipids
• Glucose
• Lactate
• Urea
• Pyruvate
• Creatine

• Creatinine
• Glycogen
• Uric Acid
• Vitamin Sterols

6
Skin Cross Section
7
Types of Fingerprints Left at the Crime Scene

• Latent print impressions
• Patent print impressions
• Plastic print impressions
• Katent print impressions

8
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

9
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

10
Katent Prints

• 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

11
Latent Prints

• Prints not visible to the naked eye
• Prints need to be made visible
• throughpowders, chemical processes, or lasers
• Most common type of impressions left at crime
  scenes.

12
Non-destructive Methods of Lifting Prints

• Visual exams
• Alternate light source (ALS)
• Photography

13
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), 1,8-diazafluorenone (DFO)

14
What to include on lift card

• At a minimum include
• Case
• Date
• Print /letter
• Initials of lifting technician

15
Practice lifting using conventional powder after
being shown the technique using a slide
16
Practice lifting using magnetic powder after
being shown the technique using a slide
17
Chemical Lifting Techniques

• Use with porous objects

18
Iodine

• Not really a chemical reaction
• Temporary
• Place a few crystals in closed container with
  object.
• Iodine sublimates
• Photograph print to preserve it

19
AgNO3(aq)

• Cover area with solution (we will use a brush)
• Expose area to high energy (e.g. UV) light source
  (be careful not to overexpose print)
• Photograph to help preserve
• AgNO3(aq) reacts w/ salts that are present
• AgNO3(aq) Cl- ? AgCl- UV ? 2AgCl?
• 2Ag0 Cl20

20
Ninhydrin

• Ninhydrin dissolved in alcohol (ethyl, isopropyl,
  methyl, or butyl alcohol)
• Reacts w/ amino acids in print (forms Ruhemann
  Purple)
• Place object in solution (or spray solution on
  large object, wear protection) to soak
• Allow object to dry (warm humid area best)
• Iron object with steam setting (introduces warmth
  humidity)

21
Ninhydrin reaction
22
Sample results for Ninhydrin
23
2 more photographic processes

• 1-8, diazafluoren-9-one (DFO)
• Physical Developer (PD)
• Both react with salts that are left in the prints
• Used more often than AgNO3(aq) but similar
  processes

24
Gentian violet (crystal violet)

• Stains fats/oils left behind
• To make solution- .02g/80mL dH2O
• Used for finding prints on sticky side of tape
• Place tape piece in solution
• Rinse tape with water
• Photograph prints that are present

25
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