Latent Evidence

The Latent Evidence Section is under the direction of Special Agent in Charge John Byrd. The Latent Evidence Section is involved in the development and identification of latent fingerprints, palmprints and sometimes even foot prints. This 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 by the unaided eye or without some means of development (either chemical, physical, photographic or electronic). This is usually true and the Latent Evidence Section employs over forty different methods in order to develop this often fragmentary and elusive evidence. This is quite a change from just twenty years ago, when most labs used only four or five methods to develop latent prints. Some methods in use on a daily basis in the crime lab involve magnetic and fluorescent powders, alternate light sources, superglue processing, dye stain techniques and computerized digital imaging. The goal is to always detect and capture that faint and at times almost nonexistent latent trace of a fingerprint.

Once a latent print is located, it is the job of the analyst to use some means to record or preserve it for future comparisons. This is accomplished by using photography, physically lifting the print from the surface it was detected on or by electronically converting it into a digital image and storing it on a computer hard drive or other electronic media.

The entire value of latent prints in the forensic world 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, baring any injury, fingerprints remain the same from birth until death (and after). With these facts as a basis, 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 (there are eight pattern types that all fingerprints fall into), 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 small details are found to be constant in both prints without any unexplainable differences, then the prints can conclusively be said to have a common origin (in other words, they were made by the same person).

Many times, a latent print may be recovered from a crime scene, but the investigator has no clue who left the print. In the past, this presented a real problem as the latent print could not be compared to each and every person who had known inked fingerprints on file. With almost five hundred thousand fingerprint cards to look at, the process of comparing them all to a single latent print would be impossible. Computer technology has overcome this seemingly insurmountable problem in the form of the Automated Fingerprint Identification System (AFIS) and the Integrated Automated Fingerprint Indentification System (IAFIS). IAFIS is a network link used to search the master criminal fingerprint files of the Federal Bureau of Investigation. Since computers can perform tasks at speeds a human cannot approach, the idea of looking for a match through a file of thousands of fingerprints has become a reality. With the use of 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 and the fingerprint analyst examines each one in an attempt to identify the unknown print. The computer is not a substitute for the trained analyst, it is only a tool used. The latent print analyst is still the one to determine if any of the resulting fingerprints match the unknown. Through the use of AFIS technology, crimes that previously remained unsolved are now being closed and arrests made.

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 extremely 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 are the same (or nearly so) for all shoes or tires of that particular style. The individual characteristics are those things that 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 that were made while it was in use and is completely random in nature. By looking at these 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.