LATENT PRINTS
Fingerprints are the most valuable source of identification. There are so
many occasions in life where we need to be fingerprinted. It involves getting
passport, the visa, the background check for a new job. Fingerprints are taken
of suspects or criminals by the Law enforcement department. Every individual
has unique and permanent fingerprints.
What Are Latent Prints?
Latent Print - A latent print is an impression made from the friction skin
(ridges of your skin) of the fingers or palms of the hands on the surface we touched.
The Oils and perspiration from body settle on the ridges of the skin and transferred
to surface we touched resulted in finger impression. They are the valuable physical
evidence that is used to solve crimes.
Types of Fingerprints found at crime scene –
Chance impressions or chance prints are the fingerprints that are left at crime scene
by the victim or criminal on objects/surfaces.
They are of three types….
1) Latent
Latent fingerprints are very important pieces of forensic evidence; they are not readily
visible to the naked eye and additional processing is required to see them. Various
methods used for their processing such as fingerprint powders, chemical reagents
or alternate light sources.
Latent fingerprint evidence is divided into two categories:
I. Porous evidence that readily allows for the conservation of latent fingerprints
because residue infuses into the surface; such as cardboard, paper and unfinished
wood and
II. In non-porous evidence latent fingerprints substances only lie on the surface
and did not infuse in to the surface and can be intentionally or accidentally wiped
away; such as glass, finished wood, and
plastic.
Generally speaking, latent prints present can be found and developed easily on
smoother and less porous surface.
2. Visible prints are found on smooth or rough, porous (such as cloth, paper or wood)
or nonporous (such as glass, metal or plastic) surface. They formed when blood,
ink, paint, dirt etc. is transferred from a finger to a surface. These fingerprints are
visible to the human eye.
3. Plastic – These fingerprints are three-dimensional plastic prints and formed on soft
surfaces by pressing of fingers on soap, wax, wet paint etc. They are easily seen by
human eyes and do not need any
additional processing for visibility.
Latent fingerprinting involves step by step process, first
locating, developing, preserving, and identifying the impressions left by a culprit
at the scene of crime.
Latent prints made visible by using various methods.
Dusting or Staining: Dusting or staining technique is done
by using various fingerprints developing powders (Black powder, Grey Powder, aluminum
powder, magnetic powder etc.) by brushing them to a surface. Powder bonds with
the print moisture and make it visible. Prints are preserved as evidence either
by photography or by lifting them with adhesive tape and transferred it on the
white or black sheet of paper (lift card) according to the contrast of the
powder.
But how to collect Patent Prints and plastic fingerprints?
Both Patent and plastic fingerprints are collected by using photography.
Using high resolution with a forensic measurement scale these prints are
photographed.
Alternate Light Source (ALS) –
Alternative Light Source is a laser or LED devices that emit
a particular wavelength, or spectrum, of light to reveal prints on certain
surfaces (doors, doorknobs, windows, railings, etc.). Experts also use color
filters and camera filters to enhance the print quality and then photograph the
same.
Cyanoacrylate
Cyanoacrylate (superglue) processing, or fuming, is a
technique to develop fingerprints on a surface before applying powders or dye
stains. This process used on non-porous surfaces, the exhibit exposed to
cyanoacrylate vapors (fumes) which will adhere to the prints and make them
visible (a milky white colored print).
Dye Stains (Rhodamine 6G, Safranin O, Thenoyl Europium
Chelate)
Dye stains used in conjunction with cyanoacrylate processing
on a non-porous surface. After cyanoacrylate fuming, a white-gray-milky print
developed which accept the dye stains causing the latent to fluoresce brighter
than the background it is located on. Expert may brush, dip, dap or spray the
dye mixture (found in liquid) on to the cyanoacrylate processed print, which in
turn take the color of the dye. Long-wave ultraviolet light source used to
illuminate the dyes to be photographed.
Chemical Developers: Latent fingerprints on Porous surfaces
such as paper can be difficult to lift with dust or dyes. In these cases
experts use chemicals methods. These chemicals react with components of latent
print residue, such as amino acids, fatty acids and inorganic salts to reveal
latent prints.
Ninhydrin reagent processed prints appeared in purple color,
which makes them easily photographed. After ninhydrin spray, latent prints on
paper appeared after being processed with a household steam iron.
DFO (1,2-diazafluoren-9-one) is used as chemical developer
to locate latent fingerprints on porous surfaces(react with amino acids present
on latent print). Latent fingerprints fluoresce, or glow, when they are illuminated
by blue-green light after DFO processing.
Other Collection Methods
Amido Black is used for developing or enhancing bloody
impressions on human skin. On cloths to reveal prints, vacuum metal deposition
using gold and zinc technique is good. AccuTrans®( a thick liquid) used to lift
powdered latent prints from rough, textured or curved surfaces, where
conventional print lifting tape encounters difficulty. It is advisable to use nondestructive
techniques before the evidence is processed with any chemical method.
In AFIS system (Automated fingerprint identification system),
we can place the latent fingerprint in to digital format with the use of
equipment such as digital cameras, computers, and scanners. Expert use this digital
enhancement imaging software to adjust various features such as contrast, brightness
and density to improve the quality of the latent print. AFIS system searches
its database for possible matches and generated a list, which verified by the
expert for traced (positive) and untraced (negative) result.
A positive result is confirmed when the latent print (found
at a crime scene) and the inked fingerprint (taken from a suspect)/ Database
print is sufficient to make a corresponding match, based on the degree of
similarity (or number of matching points) between the two prints (similar
minutia).
Latent Prints are the most valuable and common types of
physical evidence found at crime scene. All objects at crime scene are the possible
sources of fingerprints that may lead to identification of the criminal. An
expert examines the following points in latent print….
He determines the presence of latent prints (it’s partial, blurred,
smudged, fit or unfit for comparison). Compare and verify latent prints with
the prints of suspects/accused and with inmates for elimination purposes. Establish
the identity of unknown deceased persons and compare/Identify the print using
the Automated Fingerprint Identification System (AFIS).
Limitations of Latent Print Analysis
Latent print ridge analysis cannot determine:
The sex, Age, Race or nationality.
Timing of print impression (prints were left before, during,
or after a crime). Prints did not point out a specific criminal act.
MR. DEEPAK PAWAR has been working as Finger Print Expert / Police Officer in Finger Print Bureau , Delhi Police at New Delhi since 2001 . He is the senior most Finger Print Expert , attending / visited several scene of crime and solved many crime cases .He has passed M.Sc (Chemistry) and he is the Member of International Association of Identification . He is the Member of Delhi Police welfare association . He is supervising the Forensic , New Delhi District , Mobile Crime Team . He is one of the Expert in the Special Investigation Team held for investigation of important cases . He has been giving fingerprint proficient training to Delhi Police personnel's . He has been Presented / giving lectures on topics related to forensic science . He is also making examination paper of Finger Print proficient course . He is awarded with Police Medal by MHA and Delhi Police.