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Techniques for Collecting and Analyzing Fingerprints

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Racquel Manzo

on 25 October 2017

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Transcript of Techniques for Collecting and Analyzing Fingerprints

Techniques for Collecting and Analyzing Fingerprints
By: Racquel Manzo

Three Types of Fingerprints
Patent prints
are easy to locate since they are visible to the naked eye. Patent prints occur when someone has
a substance on their fingers such as grease, paint, blood, or ink that leaves a visible print on a surface
Plastic prints
are also easy to locate but are less common than patent prints since they occur when
someone touches an object such as wax, butter, or soap and leaves a three-dimensional impression of the finger on the object.
Latent prints
are the most common type of print and take the most effort to locate since they are invisible.
Latent prints occur when someone touches any porous or nonporous surface. The natural oils and residue on fingers leave a deposit on surfaces which mirror the ridges and furrows that are present on the individual’s finger
Why it is Important?
Step 3: Lifting the fingerprint
“Lifting a fingerprint” means to
make a permanent impression of the fingerprint.
Lifting a print can be accomplished on
either flat surfaces or round surfaces
. Lifting a print usually
involves a rubber tape with an adhesive surface which is applied to the fingerprint, leaving an imprint on the tape.
Often times, a flat object, such as a ruler, will be slowly swiped across the top of the tape to ensure that there are
no bubbles or ripples in the tape that will affect the imprint

Next, the tape is carefully
peeled off the surface
a plastic cover is placed on the adhesive side of the tape to prevent disruption of the print. Identification information and a description of the location of the print should be written on the back of the tape or card.

After the print is lifted, it is converted into digital data that can be modified to create a clearer image.
Step 4: Comparing the fingerprint
The final step involves a
close examination of the characteristics of the fingerprints.
The fingerprint examination process utilizes the
ACE-V method
which stands for
Analysis, Comparison, Evaluation and Verification
compare a print collected from a crime scene to a set of known prints.

A system called the
Automated Fingerprint Identification System (AFIS)
was created to
find a match to the print using a computer database.
Step 1: Locating the Fingerprint (Continued)
Investigators often follow a
two-phase process
when searching for fingerprints. The
first phase
involves looking for patent and plastic prints since they are visible. Often times, a flashlight is used during this phase. The
second phase
involves a blind search for latent prints.To narrow the search, investigators usually focus on the entry and exits points that the suspect used and any items that appear to have been disturbed, such as overturned lamps or possible weapons.

The type of surface being searched for fingerprints often determines the technique employed by investigators.

Nonporous Surfaces
Porous Surfaces
Human Skin
Textured Surfaces
Step 1: Locating the fingerprint
Step 2: Photographing the fingerprint
After the print is located, it is vital that it is
photographed before it is lifted
. A photograph captures where the print was
in comparison to other objects and captures the
of the print.

Further, a photograph can serve as a
key piece of identification
of a patent or plastic print and can be used to
compare and possibly match the print to its source
. Photographing the print’s location at the crime scene also
guards against tampering of evidence
Locating a fingerprint often requires a
vigilant and calculated search
. However, in circumstances where the print is visible to the naked eye, finding a fingerprint is relatively easy. The more intricate searches take place when the print is present on a surface but not visible.
The type of fingerprint left behind usually determines the amount of time and effort investigators must put into locating the print.
Human Skin
Porous Surfaces:
Fingerprint evidence left behind by a suspect or victim may
identify who was at a crime scene and what he or she touched.
However, it is important for
defense attorneys to know, and to inform the jury
, that the techniques used to locate and identify fingerprints are far from a perfect science. An understanding of how fingerprints are located and lifted can help attorneys recognize if a flawed analysis was performed by investigators or lab technicians. Further,
knowledge of the various fingerprint collection techniques is essential to successful cross-examination of crime scene technicians and fingerprint examiners
Patent, Plastic and Latent Fingerprints
Plastic Fingerprint
Patent Fingerprint
Latent Fingerprint
Nonporous Surfaces:
A powder technique is usually used to identify latent prints on nonporous surfaces such as glass, marble, metal, plastic, and finished wood.

Magnetic powder
technique is used in which the powder is poured on the surface and then spread evenly over the surface using a magnetic force instead of spreading the powder with a brush.

Another popular technique for fingerprint location and identification used by both lab technicians and investigators at the crime scene is
superglue fuming

Superglue fuming
is a chemical process that exposes and fixes fingerprints on a nonporous surface
In the lab, the process works by using an airtight tank,
known as a fuming chamber
, to heat up superglue (
liquid cyanoacrylate
) which releases gases that adhere to the oily residue of print, thereby creating an image of the fingerprint.
Locating and identifying fingerprints left on human skin is incredibly difficult.
The first major obstacle is finding the print since the
oily residue left by fingers that creates the fingerprint itself is often present on human skin
, making it difficult to create a contrast between the surface (skin) and the print. Further, after a print is left on human skin, the
oily residue often disperses and is absorbed into the skin
blurring the print
. Two hours is the maximum amount of time that a print on skin may be viable.
Textured Surfaces
First, you find a lifting technique that can work best for the difficult surface. That can narrow down the techniques to a minimum such as:
latent powder
flourescent magnetic powder
magnetic powder
AFIS and etc
Each technique
has to be tried
to try to lift off the fingerprint because some way and somehow you will be s
uccessful and get the print or non successful and not get a print

Three Fingerprint Patterns
65% of all fingerprint patterns are loops-
have 1 Delta
30% are whorls-
Have 2 deltas
only 5% of fingerprint patterns are arches-
have NO deltas
Fingerprint Characteristics
These are used to classify what type of characteristic each fingerprint is.
Everyone has a
fingerprint on each finger and each toe.
fingerprint is the
, even
will never change
even when you have a cut or burn.
Finally, you are now familiar to one of many jobs in the Forensic Science field. Also, you now know how to collect and analyze fingerprints at a crime scene!

Now you can practice and see what kind of fingerprint you have!
Investigators often use chemical methods to locate the print such as
iodine fuming, silver nitrate, or ninhydrin.
When one of these chemicals comes into contact with the chemicals present in the fingerprint residue (natural oils, fats), the print become visual.

Iodine fuming
takes place in a fuming chamber. The process works by heating up solid crystal iodine which creates vapors that adhere to the oily residue of print, producing a brown colored print.
One of the drawbacks of using iodine fuming is that the
print fades quickly after the fuming takes place and therefore must be photographed quickly.

Silver nitrate
, when exposed to latent prints, reacts with the chloride of the salt molecules found in print residue, forming silver chloride. When exposed to
ultraviolet light, silver chloride turns black or brown, making the print visible

is more commonly used than iodine fuming and silver nitrate techniques to locate a latent print.
The object on which the print is located can be dipped in or sprayed with a ninhydrin solution, which
reacts with the oils in the print’s residue to create a bluish print.
Fingerprint Background
1882 -
Alphonse Bertillion
, devised
method of body measurements to produce a formula used to classify individuals

This method of classifying and identifying people became known as the
Bertillion System

1903 –
The William West

Will West Case at a Federal Prison in Leavenworth, Kansas, changed the way that people were classified and identified. When a man named
Will West
entered the Leavenworth Prison inmates. His face was photographed, and his Bertillion measurements were taken. Upon completion of this process, it was noted that
another inmate
, known as
William West
, who was already incarcerated at Leavenworth, had the same name, Bertillion measurements, and bore a striking resemblance to Will West. The incident called the reliability of Bertillion measurements into question, and it was decided that a more positive means of identification was necessary. As the Bertillion System began to decline, the use of fingerprints in identifying and classifying individuals began to rise.
After 1903, many prison systems began to use fingerprints as the primary means of identification.
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