Download Fingerprint Detection and Processing

Fingerprint Detection and
Processing
Fingerprint 2
Fingerprints as
Evidence
• Three forms
– Visible prints
• Found with the naked eye
• Made after ridges come in contact with a colored
material
– Plastic print
• Left on a soft material like putty, wax, etc.
– Latent
• Left after body perspiration or oils touch the
surface of an object
Processing
Techniques
• Fingerprint “lifting” consists of many
techniques from the simple to the very
complex
• Technique used is dependent upon the
type of material, quality of print and
environment
• Many techniques (esp. chemical) are
temporary and must be photographed
immediately
Processing
Techniques
• Powder
– Among the most common and easiest to use
– Powders come in dark and light forms
• Correct choice depends on the color of the surface
– Uses dusting brush
• Lightest touch must be applied
• Powder evenly spread over the print
• Powder will stick to the oils in the print
– Print is lifted with ordinary cellophane tape
Processing
Techniques
• Iodine Fuming
– Oldest chemical technique
– Iodine crystals sublimate in air
– Will react with either the
perspiration or fatty oils in the
print (still not clear which is
correct)
– Very effective especially if
heated inside a fuming chamber
– Must be photographed
immediately since prints will
fade rapidly
• Can be “fixed” with a 1% starch
A laboratory-grade
solution
fuming chamber
Note: Iodine fumes are poisonous and should not be
Processing
Techniques
• Ninhydrin
– A chemical that reacts with amino acids
in perspiration
• Reveals purple/blue prints
• Usually sprayed on the object
– Development may take several hours
– Technique has been used successfully
on 15 year old fingerprints
– Very good for lifting prints from paper,
cardboard
Note: Ninhydrin solutions are mildly poisonous and exposure should be
minimized.
Processing
Techniques
• Cyanoacrylate
– Commercial super glue
– Will produce fumes if heated or
dripped on to a cotton ball treated
with sodium hydroxide
– Fumes will “stick” to latent prints
revealing a white colored print
• Very popular due to ease of obtaining
materials
– Especially useful on metals, leather,
electrical tape, plastic bags
Note: Super glue fumes are poisonous and flammable in high
concentrations.
Processing
Techniques
• Other techniques
– Additional chemical
techniques exist for
almost every kind of
surface
– Use of polarized light,
UV fluorescence
– Lasers