Latent Fingerprinting and its Reliability as Forensic Evidence
Introduction
The discovery and subsequent improvement in forensic science has been a road marred with many challenges. However, despite these challenges, its acceptance as a rudimentary source of evidence in the judicial system is fascinating. Nonetheless, there are copious number of skeptics who argue that the science is based on probability; thus does not fit to be termed as an actual science. (1) Among the source of their skepticism is in evidence collection. In this work, there is an exploration of fingerprint collection on diverse surfaces.
Ways of Collecting Fingerprint Evidence from different Surfaces
Fingerprints can be identified from several surfaces, which include the porous, non-porous, and semi-porous surfaces. Each of these surfaces poses its own challenge in fingerprint collection therefore demands a differentiated approach in fingerprint collection.
Examples of porous surfaces include paper, currency, cigarette butts, fabrics, untreated wood, checks, tissue and cardboard among others. (2, 3) The beauty of porous surfaces is that the probability of finding a usable print is quite high. (2, 3) The best approach to be able to collect fingerprints from such porous surfaces is to apply a sequence of processes that follows this order. The first step is to make visual examination of the surface and its surrounding environs to identify the presence of a fingerprint. (3) In some cases, the surface may have water contamination thus a new approach is needed. (2) This includes utility of ninhydrin, a chemical reagent that actively interacts with amino acids to produce a dark purple coloration famously known as Ruhemann’s Purple. (2) Once applied, leave the surface for 24 to 48 hours in order for the print to develop. (2) Although different formulations of ninhydrin have come up over the years, the most successful so far is CFC-113 that is known with a different name as Arklone of Fluorisol. (2, 3) If the print is not quite visible, further treatment with cadmium or zinc salt solution is advisable to enhance visibility. (2)
The next type of surface under consideration is the non-porous surface. (2, 4) Non-porous surfaces include surfaces like glass, polythene bags, glazed ceramics, certain types of plastics, metal surfaces, and glossy paints among others. (2, 4, 5) As in the previous case, to identify fingerprints on non-porous surfaces, the first step should be optical observation prior to applying any other methodology or treatment therein. (2) The next step is to identify whether the surface is fixed on otherwise mobile. For fixed surfaces, despite low detection levels, powdering remains the first approach to fingerprint detection and is sprayed on the surface. (2, 4) If the surface is transportable, it should be taken to the laboratory for further processing. In non-porous processing, cyanoacrylate fuming is the most applicable and acceptable mode of treatment. (2, 4-10) Further treatment by application of luminescent stain is advisable for print enhancement. (2, 3) There are a variety of luminescent powders that are readily available so as to ease identification on colored surfaces. (2, 10) In the case of wet non-porous surfaces reagents like molybdenum disulfide suspension can be used in addition to cyanoacrylate esters like superglue. (2, 4, 8, 9). Other proposed approaches include utility of vacuum metal deposits (VMD) and fluorescent dye stain like rhodamine 6G. (2, 10)
Finally, when dealing with semi-porous surfaces, the probability of finding usable prints is also high. (2) These are surfaces that are known to absorb water in addition to absorbing water-soluble deposits that are present in sweat, which occurs slowly after being deposited. (2) These surfaces include certain types of plastics, certain types of wall paints, varnished wood, waxed surfaces and glossy finished paper surfaces among others. (2, 10) Print development is inherently dependent on the level of porosity of the surface and subsequently follows one of the methodologies described above. (10)
How the chemical composition of latent fingerprints make it possible to recover fingerprints
Apparently, latent/ invisible fingerprint/ marks tend to make deposits of a complex mix of natural secretions coupled with unknown contaminants in the environment thus leaving a distinct print. (11) Fingerprints are predominantly made of water molecules. (9, 10) Fingerprints do also contain other small amount of relatively complex chemical mixture. (9)
The source of these chemical mixtures has been found to be the sweat and eccrine glands located on the palms and fingertips. (11) These glands continuously excrete the constituents of fingerprints including water, uric acid found in urea, ammonia, glucose, sodium chloride, and phosphate. (9) It is also evident that the excretion also contains amino acids, choline, lactic acid, potassium, sulphate, and calcium. (10)
Since these excretions touch other parts of the body like the hair and other sebaceous regions, scalp, and face, they additionally mix with more components that are chemicals therein. (10) These surfaces contain chemical components like fatty acids, glycerol, wax esters, squalene, alcohols, cholesterol esters, and cholesterol, in addition to, other hydrocarbons. (9, 10)
When these chemical compositions combine, they form a unique composition that cannot be equated to other surfaces. (10) Another vital facet that needs to be highlighted is the fact that recent scientific developments have shown that each person emits a unique sweat signature; thus the variation in fingerprint. (10) This is the reason why it is possible to establish a fingerprint of another person on a subject’s body. (9)
The beauty of such uniqueness in chemical composition is the fact that different degrees of element tend to react differently with different elements. (9, 10) Take for example, when conducting photometric evaluation while using UV light, different chemical compositions offer different reflection and refraction of light; hence the design of a fingerprint will emerge from the reflection against the ridges and contours of the finger. (10) In an experiment using chemical composition of the fingerprint, it emerged that squalene had the largest peak measured against a chromatogram as compared to other chemical compositions. (9) In the samples tested, palmitoleic acid (unsaturated C14), myristic acid (saturated C14), palmitic acid (saturated C16), stearic acid (saturated C18), and oleic acid (unsaturated C18) were present chemical compositions. (9) The presence of each of these compounds was marked by the rise of peak level and compared with other known levels in chromagrams of fingerprint representative samples. (9)
In another investigation, when squalene and other chemical components like hexadecanoic acid, cis-9-octadecenoic acid and octadecanoic acid were tested, it emerged that their presence was large. (10) This means that when a finger comes into contact with a surface, large amounts of sebum-rich fatty acids are deposited resulting in a gloomed fingerprint. (10) when considering the amino acid category, serine takes the lead followed closely by glycine and alanine, in addition to, aspartic acid. (10)
Given the fact that a finger contains ridges and contours, these chemical compositions are therefore deposited on each of the surfaces of the skin. Nonetheless, given that the skin is continuously emitting these chemicals, it does therefore mean that their presence is abundant on the skin and fresh. Collection can be through photography or other methods applicable to the collection of fingerprints that are at the disposal of forensic investigators/ experts.
Reliability of fingerprinting
Fingerprinting has become a relatively easy way of identifying various individuals especially in crime-related scenes. Historically, the science of fingerprinting in forensic investigation has been used as a tool in the legal system as supportive evidence in support or negation of the evidence provided. In the past years, the question of fingerprint validity was held more as an infallible facet of an absolute science. (13)
The reliability and acceptance of fingerprinting can be attributed to the increased use of biometric systems that use fingerprint scanning. (14) At the core of a biometric system is a complex probability solving mechanism that can obtain and compare information from different regions of an image that is previously stored with that which has been accepted for comparison. (14) The design of such systems is such that it can read the whorls, ridges, arches, and loops and identify their unique arrangements as per the print image. (15) Using the probability of occurrence and comparing these images, the system can determine the authenticity of an individual. (14, 15) From a naked look at the arrangements of the fingerprints, one might think that they are similar, but on a closer look, evidence of variation from one individual to the next is emergent. (14)
Individuals have accepted this system because it has made it possible to improve the security systems. For example, in computer systems, which utilize fingerprint authentication, it is almost impossible for alien people to use their fingerprint to gain access into the system unless they initiate malicious codes that allow them to either skip or alter the system biometric authentication process. (14) Individuals are increasingly using biometric authentication especially on their credit cards to thwart unscrupulous hackers who steal credit cards and use them to make purchases of goods and services. (14) Since its introduction, those who have registered under these services have little complaint on credit card anomalies as a result of individuals withdrawing their money. (14) Therefore, this translates to become confidence in forensic science identification of culprits in a crime scene.
However, the reliability of fingerprinting in identification of culprits in recent years has come under sharp criticism with many citing recent cases where judges are provided with evidence showing flaws in fingerprinting. In the works of Jones (16), it is apparent that, in the cases examined by the National Academy of Science, about 60 % people gave false information either attributable to invalid evidence or improper evidence interpretation. In this example, DNA analysis was the main issue under consideration with improper tool application that led to dismissal of several cases for flawed interpretation. (16)
Fingerprinting has been in the application for over a century in addition to palm prints and sole prints. (16) Its utility has been more pronounce in law enforcement departments in what is famously termed as the “friction ridge analysis.” (16) The comparison of ridges, whorls, loops and other points where there is similarity is used in the identification process. However, this method becomes flawed in a scenario in which the fingerprint is smudged. (13, 15, 16) When the fingerprint was first taken for storage in a biometric system, the finger was apparently clean. (15, 16) However, the region in which the print is taken from may in most cases be dirty. This means that irrespective of the difference in chemical composition of the surrounding, there is an increased probability of the fingerprint to be altered. (16) When a fingerprint is altered, it means that the regions of similarity will subsequently be altered thus when it comes to comparison with the original image, the possibility of more than one match emerging is high. (15, 16) The main reason behind this is that there are fewer points of comparison thus the likelihood of a flaw in the result.
Consider another scenario in which a fingerprint has to be sorted from many fingerprints that overlay on an individual surface. Apparently, when identifying a fingerprint, there is a likelihood of more than one fingerprint to be present. In such a scenario, when collecting a fingerprint, the likelihood of collate and isolation may yield a flawed image that will eventually lead to wrong identification. (16) Another challenge with this isolation is that the occurrence of a crime does not mean that the surface will only have one fingerprint. Consider a crime that occurs in a pub. Such a place has many visitors thus collecting fingerprint after a crime has occurred may be flawed.
Newman (15) goes ahead to identify inherent challenges in a fragmented fingerprint. When collecting fingerprint, in most cases, the fingertips are left out. (15) This means that the need to use fingerprint identification will be minimal since little image information is available. What is therefore left is for the forensic scientists to use probability and sketch probable shapes of these fingerprints that have higher chances of flawed results. (15) Consider a scenario in which a corpse is disintegrating and the fingerprints are segregated, combining them also becomes a point of challenge; thus the admissibility of fingerprint in a court of law, in such scenarios, becomes a major challenge.
Another reason this issue is raising eyebrows is the fact that judges do not have reliable information on forensic science and its audit structure. (1, 13, 17) This means that the prosecutors or defense lawyers provide whatever evidence they deem fit to win their case rather than provide comprehensive, uncensored information on inherent flaws with the method used.
Conclusion
In conclusion, the admissibility of fingerprinting as a source of evidence in court is under stiff challenge. Does this mean that the science behind fingerprinting is a scam or less scientific? Therefore, by virtue of the fact that its application on copious arenas has proven effective is a reason to believe in its authenticity. However, it is paramount that positive criticism is applied so as to harness the tools, standards, and methodologies of application. This transcends not only to the operation framework, but also to moderation and interpretation framework so that there is a better understanding of the concepts and clarification that this is an expert opinion rather than absolute evidence. This is a challenge to the forensic science community to conduct finer research on every aspect of fingerprinting, and remove any inherent flaws that can be removed to improve on public confidence through accurate information provision.
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