Which Key Piece of Evidence Can Make or Break a Case?

fingerprintsI have received so many questions, comments and emails about fingerprint evidence and crime scene investigations, so I decided to keep with the theme from one of my previous posts about fingerprints.  There is so much more the fingerprint evidence from discovery to identification.

The science of fingerprint identification is referred to as dactylography.  Fingerprint evidence is absolutely key in a crime scene investigation.   It is the most fragile piece of evidence that is searched for, documented, and collected first at the crime scene.  Environmental conditions and improper handling can contaminate it easily.  After collecting the evidence, then the difficult task of identifying and comparing begins.

The fingerprints must be grouped into one of the three main pattern categories of arch, loop, and whorl for eight different pattern types.  Each category has subcategories that interpret the established rules for the Henry classification system.

The arch is the simplest type of fingerprint pattern with two subcategories: plain arch and tented arch.  The plain arch is characterized by a side-to-side flow of ridges with less than a 45-degree angle and the tented arch flows with a sharper upward thrust of ridges at an angle of 45 degrees or more.  This pattern encompasses approximately 5% of all pattern types.

The loop, which is the most common, includes approximately 65% of all pattern types, which is then divided into radial patterns of the left slope loop and right slope loop.  A loop must have a recurve, a cross looping ridge, and a delta or the point that is the nearest to the ridge, in order to fall into this category.  Most crime scenes with developed or visible prints will fall into this main category.

The last and most complex pattern is the whorl, a definite circular pattern that includes approximately 30% of all pattern types, which divides into four specific categories: plain whorl, central pocket loop, double loop, and accidental whorl.  In addition, the whorl can be further divided into an inner or outer tracing.

Fingerprints can be located and collected from three main groups: plastic fingerprints caused by a negative three-dimensional impression such as clay or wet paint, fingerprints contaminated with foreign matter such as blood or dust, and latent prints that is generally not visible to the naked eye and must be developed by one of various developing techniques.

Latent prints are most commonly developed with various powders in several colors and lifted with adhesive tape.  The appropriate powder is charged as the excess powder is tapped from the bristles and gently dusted in the designated area with the tips of the brush.  The point of processing of the print becomes optimum when the development isn’t over processed.

Think about everywhere our fingerprints are transferred throughout the day.  Take a look at your own fingerprints and see which category it fits into.

Remember, fingerprints are truly amazing like a work of art and individual; no two are alike, just like a beautiful snowflake.


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