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Latent Evidence

The Latent Evidence Section develops and identifies latent fingerprints, palm prints, and sometimes even foot prints.  The section deals with virtually any area of friction ridge skin impressions that may be developed.

 
The word latent implies that the prints are hidden or not easily seen without help (either chemical, physical, photographic, or electronic development).
 
The Latent Evidence Section uses more than 40 methods to develop this fragmentary and elusive evidence, a change from just 20 years ago when labs used only four or five methods to develop latent prints.
 
Some methods in use on a daily basis involve magnetic and fluorescent powders, alternate light sources, superglue processing, dye stain techniques, and computerized digital imaging.  The goal is to detect and capture a faint and almost nonexistent latent trace of a fingerprint.
 
Capturing a Fingerprint
Once a latent print is found, the analyst records it for future comparisons by using photography, physically lifting the print from the surface or electronically converting it into a digital image for storage on electronic media.
 
The value of latent prints rests on two scientifically accepted principles:  first, no two persons possess the same friction ridge skin detail (i.e., everyone has different fingerprints) and second, barring any injury, fingerprints remain the same from birth until death (and post-mortem).
 
This means latent prints can be compared to known inked impressions, and identifications between the latent prints and the known prints can be established to a certainty.  This is done not by comparing the types of patterns on the fingerprints but by the arrangement of the ridge details within the prints.
 
These details, often referred to as minutiae, are the ridge endings, ridge splits (or bifurcations), ridge islands, and ridge dots that make up every fingerprint.  When these tiny details are constant in both prints without any unexplainable differences, then the prints can conclusively be said to have a common origin or, in other words, to have been made by the same person.
 
Finding a Match With No Suspect
When a latent print was the only clue, comparing it to the more than 500,000 fingerprint cards available was nearly impossible.  Computer technology solved this problem with the Automated Fingerprint Identification System (AFIS) and the Integrated Automated Fingerprint Identification System (IAFIS).
 
IAFIS is a network link used to search the master criminal fingerprint files of the Federal Bureau of Investigation.  With AFIS, a latent fingerprint can be searched through the files and a list of most likely candidates can be developed in a matter of minutes.
 
The computer provides the possible matches in the form of video images on the computer monitor.  The fingerprint analyst examines each one in an attempt to identify the unknown print.  The computer is not a substitute for the trained analyst, but it is a useful tool.
 
The latent print analyst is still the one to determine if any of the resulting fingerprints match the unknown.
 
Shoes, Boots, and Tires
Additional forensic examinations performed by the Latent Evidence Section include the examination and comparison of questioned footwear impression and questioned tire impression evidence.
 
These two disciplines are useful in connecting a suspect to a crime scene based on the shoes worn or the vehicle used.  Each of these types of examinations involves the comparison of class characteristics and individual characteristics.
 
Class characteristics include such things as the shoe sole design or the tire tread design and if they are the same (or nearly so) for all shoes or tires of that particular style.  Individual characteristics make that shoe or tire unique to any other shoe or tire.  These could be a combination of things such as cuts or nicks in the shoe or tire.
 
By looking at the unique characteristics and other factors, such as size and wear patterns, an association can be made between shoe and tire impressions left at a crime scene and the shoe or tire that was in use by the suspect when the impressions were made.
 
 
Latent Evidence Section:   Acting Forensic Scientist Manager Karen Morrow