First a basic explanation:
1. A latent fingerprint is one that is generally not visible unless it is treated in some manner. The print itself is composed of moisture—mostly water—but it also contains small amounts of the constituents of perspiration (sweat), like amino acids, choline, sodium and potassium salts and urea.
2. The palms of the hands and soles of the feet are covered with friction ridges, and these ridges have sweat pores along their surface. These two areas have one single type of sweat gland: Eccrine glands. Only water and the substances listed above are exuded from these glands.
3. Other parts of the body have two other types of sweat glands: Sebaceous and Apocrine glands. Sebaceous glands exude fatty acids, glycerides and hydrocarbons. In other words these secretions are oily in nature. The Apocrine glands secret water along with ions of sodium, potassium and iron as well as proteins, ammonia, carbohydrates and cholesterol. Sebaceous glands are associated with hair follicles.
4. When the hands come into contact with the face, arms and other parts of the body they become contaminated with this sebaceous, oily mix.
Over the years several methods for “developing” latent prints have evolved. The most often used development methods currently are fingerprint powders, chemical processing and fuming techniques. Each of these methods will be examined in more detail in subsequent articles.
You might say that locating areas that may yield latent prints requires an intuitive approach as well as some common sense. Prior to any attempts being made to recover latents the crime scene investigator (CSI) performs a walk-through of the scene, making notes of potential spots where latents may exist.
The CSI would first determine the “probable” point of entry. This would include doorways and windows, even a hole cut through the roof. Next he tries to envision the path that the perpetrator took through the scene. The very nature of the crime will assist in determining the best spots to begin the latent processing steps: A burglary will most likely mean that the subject touched or moved certain objects, opened drawers or cabinet doors. etc.; while a homicide or sexual assault would have involved very different activities.
Depending on the number and training levels of those working the crime scene, the team leader will make specific assignments. The first priority is securing the scene. This begins with establishing the exact boundaries of what constitutes the scene, and tehn setting up barrier tapes and/or posting personnel who monitor or restrict access to the areas designated as being part of the scene.
The crime scene must be fully documented prior to any type of evidence collection. Thus, the overall scene is photographed and when possible—videotaped. A rough crime scene sketch is then begun. Documentation must also include establishing a chain of custody for the evidence collected. (See related article on Crime Scene Protocol.)
This all involves time. Unlike certain TV shows, performing a complete crime scene investigation and arresting the perpetrator takes a lot longer than the hour of storyline and commercials.
Forthcoming articles will give specific information of the three principal methods of Latent Print Development mentioned above.
If you would like to learn more about latent fingerprint development techniques, you may download a free technical bulletin. Click here for access to your copy. Overview of Latent Print Development Techniques.
You may also download a complete catalog of crime scene equipment , or just the specific sections that interest you. Click HERE for access.
Don Penven is a freelance writer and photographer based in Raleigh, NC. He has over 30 years direct and indirect experience in law enforcement and crime scene investigation.
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