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Fingerprinting is a reliable and accurate method of identification. It is universal, distinctive, easy to capture and has permanence, (Jain et al, 2002). Its history can be dated as far back as the 14th Century in China. It however was first looked at as a means of criminal investigation only in 1880 by Dr. Henry Faulds. William Herscel recognized the uniqueness of fingerprints and used it as a form of signature on contracts in the 1870s. Lastly, a notable figure who made a significant contribution to fingerprinting was Sir Francis Galton. In his book published in 1892, he highlighted the uniqueness of ridge characteristics. This is later referred to as Galton's Details or minutiae. (Pike, 2007)
Before fingerprinting came about, a technique known as Bertillonage was employed to identify criminals. A form of anthropometry, it is a method where measurements of the body and other distinguishing features such as birth marks of a criminal were recorded (Pike, 2007). This system however was not always effective, as seen in the infamous case of William and Will West of 1903. This was the turning point of criminal identification and since then fingerprinting became the primary system of identification (Crime Scene Forensics, LLC).
Dactyloscopy, or fingerprint identification, involves comparing two instances of minutiae in order to establish if the impressions are from the same individual (Ashbaugh, 1999).Through Automatic Fingerprint Identification Systems (AFIS) which was developed in 1980, law enforcement agencies are able to automatically process and match unknown fingerprints against a database (Wikipedia, 2010). Future advances of this system are the possible integration of palm prints, auxiliary biometrics and digital images to increase the effectiveness and accuracy of identification (Interpol, 2010). Methods of fingerprint dusting?
Another aspect crucial to a crime investigation is blood testing. A presumptive blood test is necessary when there appears to be bloodstains found on a crime scene. Kastle-Meyer (KM) test, first identified in 1903, uses phenolphthalein, a chemical indicator, and hydrogen peroxide. If the solution turns pink, it can be certain that it is blood. Another such presumptive test is the microcrystalline test, in which the addition of certain chemicals would result in the blood forming crystals. Teichmann and Takayama are the commonly used crystal tests. The next step would be to determine if the blood is of an animal or human origin through the use of a precipitin test. After it is conclusive that the blood is indeed human, DNA profiling test is then performed (Ramsland).
The aims of this practical are to experience first-hands the different methods and techniques of fingerprint dusting, to be able to identify the different structures of fingerprints as well as to explore how the KM test is performed.
There are three main types of fingerprint structures in the Henry Classification System. The least common is the arch and it is characterized by ridges entering from one end and exiting the other. It can be further subdivided into plain and tented arch. The second basic pattern is whorls. In this pattern, some of the ridges make a complete circuit. Subgroups of whorls are plain, central pocket, double loop and accidental. Loops form the most common structure, contributing to about 70% of fingerprint patterns. Ulnar loops are more common than radial loops (Lennard, Patterson). Figure 1 shows the appearances of the different patterns of fingerprints.
Figure 1: Fingerprint Patterns
The following tables summarize the patterns of each finger and toe prints of Annex C.
Figure 2: Fingerprints Classification
It is evident from Figure 2 that all ten fingers are of the whorl pattern. Whorls are the most common after loops and having whorls for all fingers is not a rare observation (Handlines, 2005). Although they share a similar overall pattern, they are individually different from one another. Each finger has unique ridge characteristics that differentiate it from the other.
Twinned Loop Whorl
Lateral Pocket Whorl
Twinned Loop Whorl
Figure 3: Toe-prints Classification
On the other hand, the toe-prints do not share a common pattern as seen in Figure 3. Additionally, the prints of right and left feet are not mirror images of each other. Toe-prints of the right foot have two patterns (arch and whorl) whereas the left have three different types (arch, whorl and loop).
Identification and classification of prints proved to be quite difficult even though they are inked. A few of the prints are hard to make out due to very wet ink. Also, the presence of scars (especially on the fingerprints) disrupts the inked ridges, resulting in an incomplete print. Lastly, it was tricky to deposit complete toe-prints on to Annex C. Identifying the toe-prints from the annex alone provides inaccurate results because only partial impressions could be observed and these do not reflect the true nature of the toe-prints.
Annexes A, B, D and E
Latent fingerprints are not visible to the naked eye and are made when sweat, oil or other substances on the fingertips duplicate the structure and ridges of the fingerprints on a surface such as paper, glass or weapon (Watson). The natural secretions of one's soles of the feet and palms of the hands are produced by eccrine glands (Lennard, Patterson).
Because of natural oil secretion on our fingers, fresh fingerprints can be uncovered and obtained through dusting it with powders. Such powders are able to adhere to the skin oils and hence the prints are made visible (Castillo, 2007).
The latent fingerprints of Annex A turned purple when treated with Ninhydrin solution. The formation of the product Ruhemann's purple is due to amino acids present in the eccrine secretion reacting with ninhydrin. Ninhydrin is the most common method for uncovering latent prints on porous surfaces. However, it is limited in that certain type of paper surfaces like a bank note will react very strongly and hence giving inaccurate and inconclusive results (Lennard, Patterson).
From Annex A, it is noticed that the aged fingerprints (dated 7 September) produced the darkest shade of purple as compared to the more recent prints. It is not certain whether the age of the fingerprints would cause a difference in the shade of the colour. Perhaps this disparity could be attributed to the amount of oil secretion on the fingertips at the time of deposition.
Next, we will discuss dusting, the oldest method in fingerprint development. Dusting requires special skills and any mistakes can result in the destruction of a latent print. It is more effective when working with fresh fingerprints because the powders depend on the natural skin oils on the fingertips that are deposited on surfaces that had been touched (Castillo, 2007). In Annex D, dusting using black powder was used on the latent fingerprints. Black was chosen as it provides the best contrast against the white paper.
As seen from Annex D, the prints uncovered were not very visible. This could be due to the incorrect technique of dusting. Firstly, too much force was probably applied while dusting and hence the ridges are damaged. Secondly, dusting was still carried out even though the image had developed clearly. Thus more powder is being added to the latent fingerprint. These contribute to overdeveloped prints, leading to the loss of details (Newton, 2007).
Dusting using magnetic powder on the other hand yields a clearer imprint. This method is used on non-magnetic surfaces and does not damage the prints very much.
In annex B, the 3-day old print did not develop well because during the deposition, there was a mistake in rolling the big toe from side to side. The ridges of the hallux of the more recent print were much well-developed. In annex E, the fingerprints are crisper than that from annex D.
As a whole, ninhydrin test is a good means to develop latent prints from porous surfaces. As mentioned above, it cannot be applied to certain surfaces. Despite that, ninhydrin can successfully detect prints that are as old as 15 years and is the most widely used test to obtain latent fingerprints on paper (Newton, 2007).Dusting using powder can be applied to non-porous surfaces and there are a variety of colours available to provide a contrast against the surface. However, this method is very messy and under inexperienced hands, the resulting prints would not turn out well. Using magnetic powder instead proves to be a cleaner and more effective method in this practical. Because there are no brush fibers touching the surface, there is a lesser chance of exposing the latent fingerprint to further damage. One sweep is usually required to produce a dark, observable print. It also yields a crisper and cleaner print and produces good prints on textured surfaces and plastics, unlike that of regular powder. Its limitation is that it can only be performed on non-magnetic surfaces (Wertheim, 2009).
"Identical twins have identical fingerprints, just like having identical DNA."
Identical or monozygotic twins are twins that develop from a single fertilized egg or zygote which then splits into two separate embryos. Such twins are genetically identical because they are the product of a single egg/sperm combination. This is different in the case of fraternal or dizygotic twins, which result from two fertilized eggs (Fierro, 2010).
Although monozygotic twins share nearly identical deoxyribonucleic acid (DNA) and similar physical features, their fingerprints differ from one another. This is because fingerprint is a phenotype; meaning that it is an observable characteristic or trait of an organism. The interaction between environmental factors and the organism's genes contribute to the phenotypic expression. Therefore fingerprints are even more unique than DNA.
It is to be noted that even though the fingerprints of monozygotic twins are not identical, they are however more similar than non-related people (Kruszelnicki, 2004). The genes determine the general characteristics of patterns of the fingerprints and these start to emerge when the skin on the fingertips differentiate. The environmental conditions in the mother's womb also contribute to fingerprint structure. The formation of fingerprints begins 7 weeks into pregnancy. About 60-70% of monozygotic twins share the same placenta but different amniotic sacs (Wikipedia, 2010). The flow and position of amniotic fluids are not constant during cell differentiation. The fingertips too are in contact with other parts of the foetus and the mother's uterus, and the position of the foetus always fluctuates. This results in the cells differentiating and growing in a microenvironment that differs slightly from hand to hand and finger to finger (Jain et al, 2002). Thus the microenvironment provides the fine details of the structure of fingerprints (Richards, 2005). Other environmental conditions include blood pressure, nutrition and the rate at which the fingers grow at the end of the first three months of pregnancy (Fierro, 2010).
The following highlights the significance of an environmental factor in the formation of fingerprints. Identical twins will receive different blood flow as the size of umbilical cord varies for each. If blood flow is constricted, the lower part of the body of the foetus will experience a decrease of flow so as to preserve blood for the brain. Consequently, this causes more blood flow into the arms and therefore bigger fingers will develop and it is more likely that they will have a whorl pattern. If there is a lesser blood flow, the finger pads are flattened and have a higher chance of forming an arch or loop pattern (Kruszelnicki, 2004).
Kastle-Meyer (KM) test is a forensic presumptive blood test. It is used to confirm whether the substance is blood or otherwise. The three reagents that were used in the test were ethanol, reduced phenolphthalein and hydrogen peroxide (in that order). It relies on the fact that haemoglobin in red blood cell acts like a peroxidase and is able to catalyze the oxidation of reduced phenolphthalein. Ethanol is first added to lyse the cell, further exposing the heme group and hence increasing the sensitivity of the test (NFSTC, 2010). In the presence of hydrogen peroxide, haemoglobin catalyzes the oxidation of phenolphthalin, changing the yellow colour to intense pink. The oxidation reaction is catalyzed by haemoglobin when it cleaves oxygen from hydrogen peroxide. This is the observation if the specimen is indeed blood (Gallagher, 2009).
From the results in Table 1, sample 1 (blood) reacted to the reagents as predicted. Upon the addition of reagent 3, blood immediately turned to a dark shade of pink. There was no colour change for ketchup. Ribena turned colourless whereas beetroot and red cabbage turned yellow. Theoretically, beetroot and cabbage should give false positive result and turn to pink as they are vegetables and contain oxidases. A probable explanation for such inconsistency could be due to the fact that they are mild oxidases and hence the colour change will be observed after 30 seconds.
One advantage to this test is that it can detect blood as diluted as 107 times. Yet it is not without limitations. Firstly, the test is sensitive but not specific. Secondly, it will produce a false positive result as long as the substance contains oxidizing agents. Hence vegetables such as cauliflower and horseradish when subjected to the KM test will undergo a colour change to pink. Lastly, the test is not able to distinguish between animal and human blood thus requiring further tests like Ouchterlony Test to be performed. For these reasons, results of the Kastle-Meyer test should not be a conclusive evidence for the confirmation of blood (Wikipedia, 2010).
Fingerprint lifting is a process in which copies of fingerprints found in a crime scene is being secured. Not only is this a crucial piece of evidence, it also increases the chances of identifying the person who might be connected to the crime.
It takes great skill and care to lift prints as they can smudge easily, thus rendering them useless (Tatum, 2010). Air bubbles that are trapped will result in the formation of shallow craters. The lifted print is not destroyed but problems may arise when photographs are being taken (BVDA).
In the practical, thumbprint that was dusted with magnetic powder was chosen. Compared to the other that was dusted with black powder, the magnetic-powdered print was clearer and was not overdeveloped. Some problems were also encountered during the lifting process which results in the formation of air bubbles. The base layer was accidentally released before it could be carefully pasted onto the tile.