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					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
• • • • 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
• • • • 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), 1,8-diazafluorenone (DFO)

What to include on lift card
• At a minimum include:
– 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

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


				
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