This document discusses latent fingerprint identification methods and techniques. It covers the anatomy of skin and fingerprints, the three main types of prints found at crime scenes, and the components present in fingerprints that identification methods rely on. It then describes the three most common techniques used to visualize latent fingerprints: powders, fuming, and dips or sprays. Specific chemicals and processes used in each technique, like iodine fuming or ninhydrin dipping, are outlined. The goal is to detect the fatty acids, proteins, and other materials in fingerprints to lift or photograph prints for identification.

1. Latent Fingerprinting
Methods and Techniques
This presentation includes mildly graphic pictures

2. Behind the Prints
Skin has two layers:
• epidermis (upper/outer)
• dermis (lower/inner)
Feet and hands have
specialized skin called
friction ridge skin. These
ridges originate in the
dermis.
Skin contains three types of glands:
• eccrine
• sebaceous
• appocrine

3. Latent Print Identification
• there are three types of prints potentially found at a crime scene
visible plastic latent
• from fingers, palm, or feet (thumb print is best for identification)
• fingerprints are unique to an individual
• fingerprints fall into 3 major categories: arches (5%), loops (60-
65%), and whorls (30-35%)

4. Fingerprints
Methods of fingerprint identification rely on materialMethods of fingerprint identification rely on material
present in prints:present in prints:
a. Fatty acids “oils” C-C-C-C-C-C-C…
b. Amino acids -- from protein
c. Urea -- found in urine and perspiration
d. Inorganic salts -- sodium chloride (NaCl),
perspiration
Each print contains about a microgramEach print contains about a microgram
((µµg) of material depending on pressure andg) of material depending on pressure and
glandular activityglandular activity

5. Fingerprints
There are three common techniques used toThere are three common techniques used to
visualize latent fingerprints:visualize latent fingerprints:
a. Powders
b. Fuming
c. Dips or Sprays

6. Powders
Most common identification method partly because they are cheap
and fast
Powders stick to the oily components of the print
Black and silver most common depending on background although
fluorescent and magnetic powders are fast becoming preferred
Must lift print with special tape or photograph

7. Fuming
Iodine
• iodine undergoes sublimation (solid  gas)
• iodine is non-polar – dissolves in the oil of
fingerprints
Superglue/Cyanoacrylate
• cyanoacrylate dissolves in the oils of
the print to form very visible white
ridges
• very sensitive method

8. Fuming
Iodine
• iodine undergoes sublimation (solid  gas)
• iodine is non-polar – dissolves in the oil of
fingerprints
Superglue/Cyanoacrylate
• cyanoacrylate dissolves in the oils of
the print to form very visible white
ridges
• very sensitive method

9. Dips or Sprays
Ninhydrin
• intense purple good for light colored backgrounds
• sensitive to the amino acid or urea components of prints
(eccrine secretions)
• most widely used method for latent print detection from paper

10. Dips or Sprays
Silver Nitrate
• the silver reacts with chloride (in sweat to form silver chloride
which then decays into silver producing a permanent black
stain in UV (ultraviolet) light
AgNO3 + Cl
-
 AgCl  Ag (in UV)
• good for wood products, paper products, leather, and many
metal surfaces (including ammunition and casings)
• silver nitrate is generally used as
a last resort technique

11. Dips or Sprays
Crystal Violet
• also called gentian violet
• stains fatty acids and protein components of fingerprints
• purple solution is best for detecting latent prints on all types of tape (duct,
Scotch, masking, electrical, etc)
• permanent stain is dissolved in alcohol before use
Amido Black
• black protein dye best for blood-contaminated latent prints
• good for non-porous surfaces (metal, plastic, glass)
• corrosive – it will damage surfaces, collect samples of blood for typing or
DNA fingerprinting first

12. Dips or Sprays
Fluorescent / Luminescent Chemicals
• fluorescent – reradiation of light; luminescent – produces light by chemical
means
• dyes adhere to fatty acids; most common are Rhodamine and Ardrox (both
fluorescent)
• extreme sensitivity
• must be viewed under alternate light source (black light, UV, laser)
before after

13. Superglue fuming, fluorescent
powder, UV light, orange filter
These techniques can be
used in combination…