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Abstract
Different types of practices are used to collect the evidence at the crime scene. One of these practices is fingerprinting. Fingerprinting allows detection and fixating human fingerprints that are left by the friction ridges. There are four different approaches in fingerprinting: chemical lifting, cyanoacrylate fuming, visualization/lifting in blood and visualization/lifting on human skin. Each of these types is designed to detect and capture fingerprints left on different kinds of surfaces. Furthermore, every type involves certain methods and instruments to fixate and lift fingerprints. This research will be focused on describing each type of the fingerprinting methods while focusing on peculiarities that each practice has. Also, the process of casting a mold of tire and footwear impressions will be described in detail.
Fingerprinting
The type of fingerprints collection method that is used in the crime scene is often determined by the surface it is left on. The surfaces, in turn, vary in significant numbers. Fingerprints may be left on glass, marble, metal, plastic, finished wood, etc. These surfaces are called nonporous. Other types of surfaces are called porous. These surfaces will deform under pressure, therefore, creating a fingerprint (Sheridan, 2013). Porous surfaces include soft materials such as butter, clay, soft metals, cement, soil, etc.
Nonporous surfaces are generally the areas that are searched for the fingerprints. However, it is much easier to detect and collect fingerprints on porous surfaces. For the nonporous surfaces, forensic science recommends using the most common chemical lifting practices such as dusting with fingerprint powder (NFSTC, 2013). This powder may be made of black granular, black magnetic, aluminum flake or other materials.
The process of using the fingerprint powder consists of applying the powder that will stick to the human skin grease and will not reside on the adjacent surfaces. Therefore, the fingerprint is made visible. Specialists then proceed to take photographs of fingerprints that are then analyzed and stored in the police database. However, using the fingerprint powder may contaminate the print area making fingerprint’s quality unacceptable. If there is a possibility of contamination, the recommended course of action is to use cyanoacrylate.
Cyanoacrylate, as well as other chemicals used in the process of fingerprint detection, is used to make the latent fingerprints visible without causing additional contamination of the crime scene and the area in which a fingerprint is found. Applying chemicals to fingerprint area causes the reaction which only highlights the outlines of a fingerprint. As well as in the procedure of dusting, highlighted fingerprints are then photographed and passed to further departments for analyzing and storing.
Another common area to look for fingerprints is blood residue. Fingerprints left in blood stains are often too poor in quality to be immediately collected by photographing them. There are, of course, some cases when blood stains are left on transparent sources or the sources that are highly reflective. Blood fingerprints are mostly collected by using chemicals such as amido black, heme specific dyes and others (Dhall, Sodhi & Kapoor, 2013).
For an extended period of forensic science history, collecting fingerprints from human skin was considered to be impossible. However, the researches of German Federal Criminal Police achieved success in inventing the procedure of detecting and lifting latent fingerprints in the postmortem casework (Färber, Seul, Weisser & Bohnert, 2010). The experimental procedures involved using adhesive powders that reacted with the residual fluids and grease creating a visible fingerprint. Therefore, fingerprints left on the human skin became detectable and collectable. Due to the characteristics of human skin surface, the application of fingerprint powder is not possible as the dust will spread on the skin without highlighting the fingerprints. Therefore, the usage of chemicals that react to different types of residual fluids is prescribed by the forensic practices.
Another important part of fingerprinting is composing and processing the documentation that makes the procedure of investigation much less complicated. The documentation generally contains taken actions, gathered data, and achieved results. The starting point of creating documentation regarding fingerprints must be the crime scene. This documentation provides basic information that is collected on arrival to the crime scene such as case number, address, information about the victim, time of arrival and departure of LPE, and the name of LPE (U.S. Department of Justice, 2012). Additionally, documentation regarding evidence must include the location of items and their condition preceding the collecting procedures. Documenting the crime scene may be achieved by making photos, sketches or taking notes that describe the crime scene. When all of the documentation is composed, it must be placed in the temporary storage for further transportation.
Casting
Although fingerprints are considered to be the most reliable and sufficient source of evidence in many cases, additional pieces of evidence may be crucial to the investigation. There are two types of evidence that is somewhat similar to the finger ridge impressions, namely tire and footwear impressions. These pieces of evidence may provide additional information about the criminal which will contribute to solving the case. However, there are certain difficulties that forensic units face when the need to collect tire and footwear impressions occurs. The impressions left by tires and footwear mostly remain in the soil which makes detecting and extracting them much harder. Nevertheless, forensic science provides different types of materials as well as different approaches to efficiently collect the impressions.
The primary procedure that is used to collect such pieces of evidence is casting a mold. It is achieved by filling the area in which the prints are found with precisely mixed water and dental stone or sulfur. Yet it is obligatory to thoroughly document the area before casting by taking photographs or making sketches. This obligation is due to the fact that casting procedure is relatively dangerous regarding contamination and deformation of the impressions. In case if any damage is done to the area of impression, photographs and sketches may provide the information to recreate or correct the molds.
A number of steps needed to cast a mold may differ depending on the type surface the impression was found in. Such surfaces may include snow, sand, soil, etc. Since impressions may be frail due to the nature of the material, it is recommended to fixate the impression by applying fixatives such as hair spray or others. The procedure includes pre-mixing the materials that will be used, pouring mixed materials into the impression, etching the needed information (date, case number, item number, officer’s initials) on the mold, and mold extraction (Warrington, 2015).
Pre-mixing materials must be completed using mixing containers, measuring cups, stirring spoon or stick, and a hot plate or stove to melt the sulfur if it is used instead of the dental stone or together with it. The mixture must not be directly poured into the impression because this will most likely result in deformation and, therefore, poor quality of the mold. It is necessary to apply the mixture on the outside surface and direct the flow into the impression. The mold must then dry up. More extreme temperatures result in faster drying. The finished mold must be carefully retrieved to prevent any damage. This concludes the procedure of casting.
References
Dhall, J. K., Sodhib, G. S., & Kapoorc, A.K. (2013). A novel method for the development of latent fingerprints recovered from arson simulation. Egyptian Journal of Forensic Sciences, 3(4), 99-103.
Färber, D., Seul, A., Weisser, H., & Bohnert, M. (2010). Recovery of latent fingerprints and DNA on human skin. Journal of Forensic Sciences. Web.
National Forensic Science Technology Center. (2013). A simplified guide to fingerprint analysis. Web.
Sheridan, S. (2013). Techniques for collecting and analyzing fingerprints. Web.
U.S. Department of Justice. (2012). The Fingerprint Sourcebook. National Institute of Justice: Author.
Warrington, D. (2015). Casting: Essentials. Web.
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