4.3 Wherever You Go, You'll Leave A Mark

Hey guys ^.^

This is an extra information that I added. (:

When victims are found fresh, we can use another method call.....

Fingerprint Analysis

Fingerprinting analysis has been used for more than a century, yet it is still widely used in law enforcement agencies.  Because of its unique characteristic, it is conclusive evidence and a valuable tool among advanced technology even today. 

However, there is a chance it might lose its ground by DNA fingerprint, which is more sophisticated and accurate than traditional fingerprint.

There are 3 types of fingerprints that exist at crime scenes:

  1)   Visible prints are made from finger stained with colored materials such as ink, blood, and grease. 

  2)    Plastic prints are formed by pressing onto a soft surface such as clay, soap, and wax. 

3)    Latent print is an invisible print left on an object by the body’s natural greases and oils.  Because it cannot be seen by naked eyes, fingerprint powders, chemicals, and even lasers are used to make it visible on the crime scene evidence.

Loops (65%)	Archers (30%)	Whorl (5%)
Lines that enter and exit on the same side of the print	Lines that start on one side of the print, rise into hills and then exit on the other side of the print	Circles that do not exit on either side of the print
Subdivided into: Radial loop Ulnar loop	Subdivided into: Plain arch Tented arch	Subdivided into: Plain whorl Central pocket whorl Double loop Accidental whorl

SIMPLIFIED FINGERPRINT ANALYSIS

WHY USE FINGERPRINTS IN A IDENTIFYING MURDER VICTIMS

According to most professional criminal investigators, fingerprints obey three fundamental principles. These principles are:

1. A fingerprint is an individual characteristic. It is yet to be found that prints taken from different individuals possess identical ridge characteristics (even in twins).

2. A fingerprint will remain unchanged during an individual’s lifetime. (The friction ridges which create fingerprints are formed while inside the womb and grow proportionally as the baby grows)

3. Fingerprints have general characteristic ridge patterns that permit them to be systematically classified.

The individuality of any fingerprint is based not upon the general shape or pattern that it forms, but instead upon its ridge structure and specific characteristics (also known as minutiae).

The recognition of these ridges, their relative number, and the approximate location of them, on the observed print, are the special characteristics that make the fingerprint a specific identifying characteristic of each individual.

There are at least 150 individual ridge characteristics on the average fingerprint. If between 10 and 16 specific points of reference for any two corresponding fingerprints identically compare, a match is assumed.

 

Surfaces Characteristics & Collection Methods

Characteristics of the surface in which the print is found are important in deciding which collection methods should be employed on scene.

The general characteristics of the surface are: porous, non-porous smooth and non-porous rough.

Porous	Non-porous
	smooth	rough
Able to absorb liquid	Not able to absorb liquid
Scientist sprinkle chemical like nynhydrin over the prints and then take photographs of the developing fingerprints	Experts use powder-and-brush techniques, followed by lifting tape	Same powdering process should be used, but gel-lifter or Mikrosil is used to effectively left a print
Paper, cardboard, untreated wood	Varnished, painted surfaces, plastics and glass	Vinyl, leather, other textured surfaces

Analysis of Collected Prints

During analysis, examiners determine whether there is enough information present in the print to be used for identification.

This includes determining class and individual characteristics for the unknown print.

The three fingerprint class types are arches, loops, and whorls. They are tiny irregularities that appear within the friction ridges and are referred to as Galton's details. The most common types of Galton's details are bifurcation, ridge endings, and dots or islands.

Classical method for developing latent prints on paper or other porous object by using nynhydrin

Check out this video to learn the technique of Using Mikrosil to Lift Fingerprints from Irregular Surfaces. (:

Comparison of Prints 


After an examiner completes the analysis, they compare the unknown print side by side with a known print. The unknown print is the print found at the crime scene, and the known print is the print of a possible suspect.

First, the class characteristics are compared. If the class characteristics of the two prints are not in agreement, then the first print is automatically eliminated. If this is the case, another known print may be compared to the unknown print. If the class characteristics appear to match, the examiner then focuses on the individual characteristics. They look at each individual characteristic point by point until they have found a possible match.

Evaluation of Comparison


After the examiner completes the comparison, they can make a proper evaluation.

Scenario 1 -Exclusion

If there are any unexplainable differences between the unknown and known fingerprints, then they can exclude the known fingerprint as the source. This means that if the class characteristics are in disagreement, then the conclusion would be exclusion.

Scenario 2 - Identification

However, if the class characteristics as well as the individual characteristics are in agreement and if there are no unexplainable differences between the prints, the conclusion would be identification.

Scenario 3 - Inconclusive

In some cases, neither of these conclusions is possible. There may not be a sufficient quality or quantity of ridge detail to effectively make a comparison, making it impossible to determine whether or not the two prints came from the same source. In these instances, no conclusion can be made and the report will read "inconclusive."

Verification of the Evaluation 


After the first examiner reaches one of the three conclusions, another examiner must verify the results. During this verification process, the entire exam is repeated. The second examiner does the repeated exam independently from the first exam, and for an identification conclusion, both examiners must agree. If they agree, the fingerprint evidence becomes a much stronger piece of evidence if and when it goes to court.

Databases such as AFIS (Automated Fingerprint Identification System) have been created as ways of assisting the fingerprint examiners during these examinations. These databases help provide a quicker way to sort through unlikely matches. This leads to quicker identification of unknown prints and allows fingerprints to be as widely used as they are in criminal investigations.

Picture from: http://forensics4fiction.files.wordpress.com/2011/08/dsc_0100.jpg

After reading this post, i'm sure that we will understand more and know how things in the  TV series CSI works. 

Have fun reading. (:

DI.

References:

http://sites.bergen.org/forensic/fingerprint.htm (lat visited 11 Oct 2013)

http://www.handanalysis.net/beginners/fingerprint_types.htm

http://www.crimemuseum.org/library/forensics/fingerprints.html (last visited 11 Oct 2013)