Light Source for the development of latent figerprints

2. Development of Latent fingerprints through
Alternative light sources (Part-I)
By-
Vaishnavi Puli
Member of Applied Forensic Research
Sciences

3. Content
• Introduction
• Fingerprint enhancement by optical and specialised light
sources
• Application of lasers to fingerprint detection
• MCQ

4. Introduction
• Inspite of the scientific developments done in the field of DNA Profiling, fingerprints are the
best evidence needed in personal identification in the field
• Fingerprint detection has improved significantly over the last two decades due to consultant
efforts by a no.of research groups all over the world.
• A wide range of physical, optical and chemical techniques are available for the detection and
enhancement of latent fingerprints
• The application of techniques like chemical reagents may increase the no.of latent fingerprints
detected there by improving their quality and finally enhancing them. And it is important that
each process is applied in a systematic order as the incorrect choice or application of one
method can destroy the later use of another technique or decreases it's effectiveness.
• The use "OPTICAL " techniques and procedures during the fingerprint detection should be
heavily emphasized as these are "NON-DESTRUCTIVE" in nature and considerably improves
the results obtained by physical or chemical methods.

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• The choice for the best detection techniques depends on the circumstances
from where the latent fingerprints and the depends on the factors like:
• 1. The type of surface on which latent print is present i.e., whether it porous,
non-porous, rough or smooth surface.
• 2. Occurrence of any specific contaminant like blood.
• 3. Probable age of the fingermark.
• 4. The environmental factors.
• The methodology of laser detection of latent fingerprints is based on the
principle that a luminescent fingerprint formed on non- luminescent surface
produces laser excited florescence.
• The florescence so produced provides intrinsically such a high sensitivity that
fingerprints are detected on typical and unusual surfaces too.
• The method also ensures detection of weak and old fingerprints.
• Laser technique is often used as a supplement to conventional procedures of
latent fingerprints defection.

6. 2. Fingerprint Enhancement by optical techniques &
specialised light sources
• Simple observation of an object under wide light may disclose a visible finger
mark that can be recorded without any further development.
• The more complex optical detection method may reveal the invisible marks that
may not be developed by any other techniques.
• A fingerprint detection sequence should always be start with optical technique.
• Prints developed using physical or chemical methods can generally be further
enhanced using an appropriate optical method depending on the characteristics
of treated marks like color of luminescence.
• The value of fingerprint luminescence become well understood since it was first
studied in the late 1970's .
• Although the property of luminescence is not found in case of latent
fingerprints a variety of procedures and techniques applied in the correct
sequence will result in generation of luminescent prints.

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• The heavy emphasize on luminescence is due to the much higher sensitivity that
can be achieved when compared to conventional procedures that result in a
color print.
• The application of luminescence techniques requires the use of high intensity
light sources. While large and expensive laboratory based were prepused in
early 1980's for this work.
• Now there are a no.of versatile cost effective alternatives such as "FILTERED
ARC LAMPS".
• Today for the purpose of fingerprint enhancement "POLILIGHT" is being used.
This light source is portable and provides a range of high intensity light bands
from the 'Ultraviolet' through to near 'Infrared'.
• In addition each band can be finctured through the fine quality interference
filters built into the system. This function is now being duplicated in other light
sources on the market.

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• Lasers are restrictive in that they only rate at a limited no.of wavelengths. As we
already known that there are THREE main types of fingerprint evidence that
may be present at crime scene they are :
1. Indented or molded fingermark
• It is 3D fingermark impression in a malliable substance such as putty or candle
wax
• Such impressions are generally being enhanced using oblique light
2. Visible fingermark
• It may be positive or negative depending on whether the fingers were contaminated
with the colored materials such as blood or whether the colored material such as dust
or soot has been removed from the surface by the fingerprint ridges.
• Enhancements of such marks can often be achieved optically depending on the
properties of the contaminant and question
• Blood is special case where specific optical and chemical enhancement procedures are
executed

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3. Latent
Fingermark
• These prints are most common and posses real dilemma
• Latent fingerprints are not visible by the naked eye , hence usually requires some
type of physical or chemical treatments and enhancements so that they can be easily
detected and visualized.
• Latent prints are formed from complex mixtures of natural secretions secreted by
the sebecious glands and also from the contaminants from the environment.
• Knowledge of the major constituents of the deposit is essential for the effective
fingerprint detection.
• Consideration of this constituents effected by different environmental conditions is
also important.
• The detection of latent fingerprints is actually quite challenging and analytical
problem. Detection of very small quantities of specific chemical compositions is
required.

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• In general terms the fingerprint powders are least sensitive of the available
techniques with 500-1000 ng of materials required for successfull detection
of latent fingermarks.
• By employing the use of chemicals for detection for example Ninhydrin such
that the color can be imported to the latent fingerprints. Generally 100-
200ng of the material is required.
• On the other hand luminescence detection using a chemical reagent such as
"DFO" is sensitive down to the 1-10 ng range also.
• The latent fingerprints deposited on the various surfaces behave differently
of different types of surfaces.
• Also in addition the various techniques employed for detection purposes are
effectively only on some surfaces but not on all.
• As a result the surface type is a major consideration. When selecting a
sequence of fingerprints detection techniques for a particular set of
circumstances.

11. 3. Application of lasers to fingerprint detection
• The most common device used for the detection of latent fingerprints on difficult
surfaces is the "ARGON-LASER".
• The surface on which the fingermark is present is illuminated with the blue-green
beam from the Argon-laser. Before the beam strikes the surface it is made to pass
through a lens, this surves 2 purposes:
• 1. It enlarges the area of the coverage of the beam so that the whole fingerprint
impression becomes exposed to the laser light.
• 2. The expanded beam protects the surface from burning.
• The imprint is observed through a safety filter. Such filters absorbs the short
wavelength components and transmits the longer ones , thus protecting the
observers eyes.
• After the fingerprint is identified it is photographed through the same filter. The
identification of fingerprint as well as it's photography is carried out in a dark room.

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• In order that light from the fingerprint ridges alone reaches . The eye the surface
containing the impression should be non-flourescent in nature.
• If the surface itself is flourescent then the ridge pattern is post treated with the a
chemical reagent so as to generate the ridge flourescence either stronger than
the background or different color.
• Alternatively the surface flourescence may be blocked by using an appropriate
filter.
• The use of lasers for fingerprint detection dates back to 1977 when it was
reported that inherent luminescence of sweat deposit may be illuminated by an
Argon-laser. No fingerprint treatment reagent was used in this investigation.
• The fact that fingerprint residue contains luminescers such as Riboflavin and
pyridoxine was considered as the possible route to fingerprint detection.
• As the luminescent components in the sweat deposit in trace amounts and
therefore the method had limited

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• It does became evident that laser technique can be used for resolution of
ridge patterns only after the latent imprint is given a post treatment. Two
broad post-treatment procedures may be used:
• 1. The latent fingerprint may be treated with a luminescent material.
• 2. The latent fingerprint may be treated with a chemical component to form a
luminous reaction product.
Blue-Green Argon laser