Latent Print Processing
Latent print is a print impression that is generated from contact of feet or hands and fingers on a surface and it is visible with the naked eye. This kind of print is widely used by the intelligent service bodies who use the latent prints to generate evidence for criminal investigation. The latent print that is generated from the different body is found to contain various chemicals that come from natural body secretions, contaminates and blood. Since the natural body secretions bear some unique chemical secretions from the sebaceous glands, they can easily be traced on different surfaces.
There are different surfaces whose classification determines the type of tests for the available prints. They are the porous, non porous and semi porous surfaces. Porous material includes the cardboards, paper unfinished wood among others while the non porous surfaces include foil, plastics, metal, glass. Scholars have also given an assurance that dry bones can also be used to generate latent print through tests on the black magnetic powder tested on both chemically preserved and unpreserved bones (Michael, 2002). Latent print easily soaks on the porous surfaces and good evidence can easily be obtained but the non porous surfaces are needed to be handled with care because the latent print may be destroyed by wiping away the surface.
There are different chemicals that are used in the processing of latent prints on different surfaces. They include acetone, glacial acetic acid, ethanol, methanol, ethyl acetate and petroleum ether reagents. There is also a number of laboratory equipment that is used in handling the substances under test brushes, bottles, dishes, fume wood feather dust, fuming chamber, oven, paper towels, humidity chambers among others, all of which are of different shapes, sizes and make.
In addition, there are the different test procedures that are used to test the samples and process quality latent prints. They include iodine spray reagent, the LCV, the ninhydrin, silver nitrate, Sudan Black, VMD, coomassie Brilliant Blue among others. The process and procedures used to generate latent print vary from surface to surface and the nature of sample under test.
Porous surface can be identified visually by iodine fuming, ninhydrin, physical developer, DFO, and inherent fluorescent techniques while non porous surface processes may include visual, inherent fluorescent laser, Cyanoacrylate fuming, vacuum metal deposition, powder, and UV light techniques. Blood stains can be tested on either of the surfaces, porous and non porous depending on the surface of which the sample has been collected.
Besides the identification of latent print source depending on the type of surface, appropriate process selection to be able to identify the best sample print source is blood, dust, grease or oil and aspiration. The best sample test for a latent print depends on the selection of both the appropriate test procedure and the selection of the sample source. However, different print samples are required to heave various tests so as to be sure of the identity resulting from the latent print test. Surface nature is an important consideration in obtaining the sample nature of the surface could be dry, wet, dirt, stickiness or grease.
The processing methodologies vary from the nature of surface and sample collected. For example, the visual technique of latent print processing includes the keen observation, to be sure of illumination. Light should be adjusted at different angles to observe any physical print. If any latent print is detected, it is photographed at once before further tests or processing. The handling procedures should be done carefully to avoid loss of essential details that are only recognizable by use of the visual method of print detection (Michael, 2002). The method is used to identify latent prints that are exposed to the surface through identification of friction ridges from fingers, feet or palms. The method discloses some marks that may not be disclosed by other methods.
The fluorescence latent print processing method is used to test characteristic features of body secretions that are present in the latent print remains. Some of these substances include the body oils, perspiration, and other secretions found on the latent print. The substances are fluorescent when subjected to laser beams. The light source incident rays are blocked by the use of special filter, and then the resulting print details are noted electronically.
The above process is advantageous as it does not interfere with the specimen because there are pretreatment procedures required before the test procedure. The method can be used on all types of surfaces and is non destructive to any further examination procedures and preserves the specimen in its original form. The fluorescence method is able to detect latent prints that are found on surfaces that can not be tested on powder. It can also be used to detect latent prints that may not be developed, the test is carried out in a dark room where expanded light beam is directed to the print surface, and then the object is viewed through a colored filter most of which is orange in color. Afterwards the latent prints are preserved by use of photographs. The fluorescence examinations are carried out on speciments that have initially been applied with fluorescent dyes, DFO (1.8 Diazafluoren) and the liquid-Drox.
Another technique of latent print test is the Alternative Black Powder method which is used for latent prints on the sticky side of labels and adhesive tapes. In this method some of the equipment and materials used include shallow dish and a small brush or camel hair, concentrated liquid detergent (liquid-Nox TM) and the light black powder. When the appropriate mixture is prepared, the mixture is applied on the sticky surface of adhesive tape by rubbing with the brush, and then it is allowed to set for close of a minute time. The tape is then cleaned with stream of slow moving clod tap water and allowed to dry. The procedure can be repeated depending on necessity (Michael, 2002). When all the necessary details are generated the spacemen can be disposed in accordance to safety rules and regulations prescribed for federal disposal rules.
Another method that is used in the identification of latent print is the Cyanoacrylate Fuming method that is also called the microburst method. This method is used in the processing of non porous surface based latent prints. The equipment and materials used include heater, fuming chamber, aluminum dish, and the chemical cyanoacrylate in the premixed state.
The methodology for this method is as described. Firstly, the aluminum dish is placed on heater whose heat settings are set to the highest level. Secondly, enough amounts of cyanoacrylate are placed on the hot dish to cover the dish bottom. Thirdly, the spacemen is placed in the hot steadily fuming cyanoacrylate and the chamber door secured. Forth, the fuming process is allowed to progress for about four minutes depending on the size of the chamber. The specimen are withdrawn from the dishes and viewed to examine any latent prints when the procedure completes, then if necessary the fuming processes can be repeated. In case there is a humified chamber, the humidity is set at 70-80 . The forensic officers are advised to be keen on the mode of disposal of the tested specimen because they could be source of problem successive firearm assessment (Michael, 2002).
Test of latent prints from blood related excretions may be done by the use of the DAB method which can be affected by either tissue method or the submersion method. The use of cyanoacrylate may be destructive to blood related print sources. Therefore, it is advisable for any test on blood prints to be tested first on the DAB tests before it is tested on the cyanoacrylate fumes. The DAB method is achieved through a series of steps which include the assembling of four trays for submersion method in each of the trays which contains different chemicals of the category A,B,C, and D. Each of these chemical samples are submerged in different solutions and analysis is done to obtain print type
In the tissue method, tissues are processed in water of different solution developers. The tissue subjected to this kind of synthesis is required to be durable to allow them to be picked easily while wet during the test without disintegrating. Tissues from a perfumed source should not be tested in this method because they produce unreliable result due to their interference with the specimen test chemicals.
The physical developer method (PD) develops latent prints found on both porous surfaces and nonporous surfaces. This is also one of the best methods used in the development of latent prints on paper money. It is usually applied after the use of the DFO method. Stains can be created on blue prints by use of special procedures of the physical developer method. The method involves a four stage mixture of chemicals which when thoroughly mixed generate a solution that is applied on the surface or the latent print is dipped in the solution and then rinsed in water after being dipped in sodium hypochlorite solution (Michael, 2002). Then the analysis is done and results issued. Correct rinsing procedure must be followed to prevent deterioration of the specimen.
Apart form the blood test procedures and the above mentioned methods, there are other methods that use powder for the tests. For example, the finger prints powders used on non porous surfaces on to which the powder is applied make the latent prints evident. The powders are usually colored and finely grounded to show clearly the marks on such surfaces once applied. Most of these powders are gray, black, white or magnetic types. The procedure here includes pouring the required amount of the powder on a surface picking by the use of brush in small amounts until the ridges of the available print start to show. When more ridges are visible the excess powder is wiped out, the latent prints are studied and a photograph can be taken to show the development. In short, there are many ways of determining the latent prints. These methods were used since time immemorial and are likely to be outdated at present.
However, with the current development on technology and advancements at the level of crime in different parts of the world there is provocation to the forensic scientists towards the development of more advanced means of identification generation. This does not sideline the finger print latent tests that have existed for centuries. The advantage is the ability of the intelligent security officers who are now able to collect data analysis and carry out comparison tests to obtain results that are not biased. The new technology uses electronics analysis mechanics that are coordinated in a logical manner to process friction ridges in a more transparent way than the original methods. The new systems are able to detect details from unknown to known end user information with blind verification (Michael, 2002). The new method is said to be good for the provision of high tolerance levels in image verification.
The current print test method like the ACE-V which is more reliable due to the nature of analysis and procedural characteristic is now the most commonly used by the forensic bodies that deal with security matters of different countries. The methods are said to be more reliable scientifically as well as very accurate. The ACE-V, for example, is a scientifically designed quality test on finger prints which is based on the analysis, comparison, evaluation and verification of impression friction ridge. It follows scientific comparison procedures.
The method allows for comparison of two items that were handled by the same person allowing another person to ascertain the comparison results. It allows for accuracy and precision in the application of the tests rather than the accuracy of the outcome. Reliance on the new finger prints gives results without the individualism of features by comparison of the analysis obtained on the friction ridge characteristics. The process starts by first the selection of friction features then testing the details of pattern type and orientation of the print. The effectiveness of the result depends on the experience of the examining officer.
The method is good in generation of print from automated systems that are able to generate more that 12 concurrent characteristic features found within the specimen under examination. It creates very clear and distinctive features for magnified images that one can easily detect the differences by mere observation of the print result. The probability of wrong conclusions is very low. It is already confirmed beyond doubts that the current system has always given the best results ever and has never in history generated similar result for different persons (Michael, 2002).
Therefore, the new system is more reliable and has a high level of accuracy. The 12 Galton scale used is excellent in the comparison and analysis synthesis of friction ridges because it gives more comparable features of the same image that uniquely relate to a certain individual. However, the full result must be accepted biologically and scientific features detail on individualism. The complete individualistic result must be confirmed fully before disclosing especially if the evidence results on the 12 Galton features issues less than 12 counts, then it should be keenly defended by the examiner who now rules out the friction ridges analysis because without the full support it could be contested.
In conclusion, the current friction print test methods are advanced, automated and more reliable in the provision of transparent results as well as accurate proofs to the legal authorities.
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