PAPER 3: FINGERPRINTS AND OTHER IMPRESSIONS MODULE 16: Detection of Blood Fingerprints

Transcription

1 Subject FORENSIC SCIENCE Paper No and Title Module No and Title Module Tag Paper 3; Fingerprints and Other Impressions, Including Biometry Module 16; Detection of blood prints FSC_P3_M16 TABLE OF CONTENTS 1. Learning Outcomes 2. Introduction 3. Blood-smeared Fingerprints 4. Detection of Blood Fingerprints with Heme-reacting Reagents 5. Detection of Blood Fingerprints with Protein-reacting Reagents 6. Summary

2 idge Characteristic 1. Learning Outcomes After studying this module, you will be able to know The significance of developing fingerprints on blood-laden evidence in crime cases. The broad classification of reagents used for detecting fingerprints on blood-smeared surfaces. Detection of blood fingerprints with heme-reacting and protein-reacting chemicals. 2. Introduction There are a host of chemical techniques for detecting latent fingerprints on different surfaces. However, if the surface happens to be stained by blood as is common at crime scenes then special procedures have to be adopted to lift the prints. Blood stains are often found on weapons, victims bodies and other articles removed from the scene of crime (Fig. 1). Fig. 1 Blood-smeared evidence are often removed from crime scenes A scrutiny of these items may also reveal bloody fingerprints. Such fingerprints are generally visible since the ridges become stained with the red color of blood (Fig. 2).

3 Fig. 2 Blood impressions are generally discernible However, if a blood-coated finger touches a surface repeatedly, the impression gets weaker and weaker. Under these circumstances, it is pertinent to enhance the impression with the aid of a suitable reagent so as to make the ridge detail clearer and sharper. The chemical reagents, which enhance the blood fingerprints often, tend to destroy or weaken the enzymes of forensic interest. Therefore, prior to fingerprint detection, blood samples from the impression should be collected for serological examination. 3. Blood-smeared Fingerprints When fingerprints impinged on a bloodstained article are to be detected, the method of choice depends on the nature of the surface and, more importantly, on the state of the coagulated blood. On coagulation, the serum content of blood separates out from the cellular content. The blood cells usually form a solid red mass, which is surrounded by a layer of straw-colored serum fraction. The serum portion is rich in soluble proteins. The blood cell fraction is rich in heme. There are two broad methods for detecting blood fingerprints: If the finger touches predominantly the red blood cells on the surface of the crime scene evidence, the print may be developed by the application of a reagent that reacts with heme content of coagulated blood. If, on the other hand, the finger comes into contact with that portion of crime scene evidence, which is coated with serum, the print may be developed by the application of a reagent that reacts with the protein content of coagulated blood. 4. Detection of Blood Fingerprints with Heme-reacting Reagents The heme moiety of the hemoglobin catalyses the oxidation of a number of organic reagents. The oxidized reaction product is normally colored and therefore renders visibility to fingerprints. Prior to 1974, benzidine (Fig. 3) was the most popular heme-reacting chemical used for detecting blood fingerprints.

4 Fig. 3 Structure of Benzidine Subsequently, however, benzidine was found to be carcinogenic and the fear of occupational exposure prompted the health authorities to ban its use a fingerprint reagent. The following heme-reacting reagents have proved useful and safe for detection of blood fingerprints. a. 3,3,5,5 -Tetramethylbenzidine The reagent, 3,3,5,5 -tetramethybenzidine, the structure of which is shown in Fig. 4 is a nontoxic and very effective in detecting blood fingermarks. Fig. 4 Structure of 3,3,5,5 -tetramethybenzidine A buffer solution containing 10% by weight of sodium acetate and 80% by volume of glacial acetic acid is prepared. To 100 ml of this solution, 2 g of 3,3, 5, 5 -tetramethylbenzidine reagent is added. This is designated as solution (A). A mixture of colloid (30 ml), ethanol (15 ml) and diethyl ether (120 ml) is separately prepared. This is designated as solution (B). The working solution is prepared by dissolving 6 ml of solution (A) and 0.5 g sodium perborate in 120 ml of solution (B). The surface is impinged 2-3 times with the working solution from a distance of about 6 inches, using a spray gun, one variety of which is shown in Fig. 5. On drying it at room temperature, the fingermarks are rendered visible. Fig. 5 A spray gun

5 b. Phenolphthalein A mixture of phenolphthalein (2 g) [Fig. 6], potassium hydroxide (20 g) and powdered zinc (20 g) is placed in distilled water (100 ml). The contents are refluxed for 2-3 hours until the formulation becomes colorless. This solution is kept in a dark colored bottle and care is taken that it remains in contact with zinc powder. Fig. 6 Structure of phenolphthalein Immediately before the fingerprints are to be developed, 20 ml of this solution is mixed with 80 ml of ethanol and 0.5 ml of 3% hydrogen peroxide. The test solution is applied to the article containing blood prints. On drying, the fingerprints become visible. c. Leucomalachite green An acidic solution of leuomalachite green reagent, the structure of which is displayed in Fig. 7, is quite effective in developing blood fingerprints. Fig. 7 Structure of leucomalachite To a mixture of diethyl ether (70 ml) and glacial acetic acid (1 ml), leucomalachite green (1g) and hydrogen peroxide (0.5 ml, 20%) are added. This working solution is sprayed on to the surface impinged with blood fingermarks. On drying, the fingerprints are visualized.

6 5. Detection of Blood Fingerprints with Protein-reacting Reagents A good number of organic derivatives bind to the protein moiety in the blood to yield colored complexes. However, blood proteins are soluble in water. Therefore, before the article under examination is dipped in the test solution, it is baked in an oven for appropriate time, depending on the reagent being used. As a result, the proteins get denatured and become fixed on the surface. Thereafter, the item is sprayed with the test solution of the reagent. The following protein-reacting reagents have proved efficient in detecting blood fingerprints. a. Amido black While using amido black reagent, the structure of which is set out in Fig. 8, three solutions need to be prepared. Solution (A) contains amido black (0.2 g) dissolved in a mixture of methanol (90 ml) and glacial acetic acid (10 ml). Solution (B) is mixture of glacial acetic acid (10 ml) and methanol (90 ml). Solution C also contains a mixture of glacial acetic acid (5 ml) and methanol (98 ml), but in a different proportion. Fig. 8 Structure of amido black The surface to be examined is baked in an oven at 100º C for about 30 minutes. It is then immersed successively in solution (A) and (B). Finally it is washed with solution (C). The surface is allowed to dry naturally whereupon the fingerprints are rendered visible. A representative blood fingerprint developed by amido black reagent is shown in Fig. 9 Fig. 9A blood fingerprint developed by amido black reagent

7 b. Crystal violet The working solution is prepared by dissolving 0. 1 g crystal violet (Fig. 10) in 100 ml distilled water. The ph of the solution is adjusted to nearly 8 by adding a few drops of 1:1 aqueous ammonia. Fig. 10 Structure of crystal violet The article to be examined is heated to about 100º C for about 30 minutes. It is then sprayed with the test solution. After 2-3 minutes, it is rinsed with distilled water. On drying the fingermarks are rendered visible. A sample blood fingerprint developed by crystal violet reagent is shown in Fig. 11 Fig. 11: A sample fingerprint developed by crystal violet on a blood-coated surface c. Coomassie brilliant blue R Two solutions are required for developing blood fingerprints with coomassie blue reagent (Fig. 12). The staining solution is prepared by dissolving 0.2 g coomassie brilliant blue R 250 dye in a mixture of glacial acetic acid (20 ml) and methanol (100 ml). The de-staining solution contains all the ingredients (in the same proportion) of staining solution except the dye.

8 Fig. 12 Structure of Coomassie brilliant blue R The article to be examined baked at 100º C for 30 minutes. It is then immersed in staining solution for 3 minutes and subsequently rinsed with the de-staining solution. On drying, the fingermarks are rendered visible. Coomassie blue reagent may also be used in concert with cyanoacrylate method of fingerprint detection. Cyanoacrylate method is based on the principle that when alkyl 2-cyanoacrylate is allowed to vaporize, it undergoes polymerization. The polymerized ester has a tendency to get adsorbed on the sweat residue, imparting a white color to the ridge pattern. The color contrast may be improved by various post-treatment methods. The surface impinged with blood prints is first baked in an oven for 5 minutes. It is then suspended from the roof of a cabinet in which is placed a china dish containing cyanoacrylate ester. The item is exposed to the vapors for about 2 hours until whitish colored fingerprint pattern develops. Thereafter, it is successively treated with the coomassie brilliant blue R staining and destaining solutions. On drying, fingerprints appear. d. Crowle s reagent Crowle s reagent is prepared by dissolving a mixture of coomassie brilliant blue R dye (0.15 g) and crocein scarlet 7B (2.5g) [Fig. 13] in glacial acetic acid (30 ml), tricchloroacetic acid (30 ml) and distilled water (920 ml). Fig. 13 Structure of crocein scarlet

9 After the article is baked at 100ºC for 30 minutes, it is immersed in the test solution for about 5 minutes with constant agitation. It is then repeatedly washed with water until the test solution background coloration disappears. The surface is then allowed to dry, upon which the fingerprints appear. e. Ninhydrin Ninhydrin technique has traditional been the most popular one for processing latent fingerprints on porous, absorbent surfaces like paper, cardboard and wood. The method relies on the reaction of ninhydrin, the structure of which is depicted in Fig. 14, with amino acid content of fingerprint residue. Fig. 14 Structure of ninhydrin The reaction produces a purple colored compound, called Ruhemann s purple (Fig. 15), which becomes deposited along the ridges, making the latent prints visible. Fig. 15 Structure of Ruhemann s purple A % solution of ninhydrin in freon-113 is sprayed on the surface containing the fingermark from a distance of about 6 inches. After the solvent evaporates, the solution is resprayed. The surface is then heated to about 80º C, without allowing it to come in contact with the heat source. Better results are obtained by steaming the article, for optimum development of fingerprints occurs at a relative humidity of 65-80%. Ninhydrin method makes it possible to develop fingerprints that are many years old. However, since the concentration of amino acids in perspiration is usually quite low, the developed prints normally do not show a sharp contrast. In order to solve this problem, the developed prints are post-treated with a Group 12 metal salt, generally zinc chloride. This interaction converts the nonfluorescent Ruhemann s purple into a luminescent complex, the structure of which is depicted in Fig. 16.

10 Fig. 16: Structure of luminescent complex formed by reaction between Ruhemann s purple and Group 12 metal salts The fingerprints developed by ninhydrin-zinc chloride method become highly fluorescent under argon laser light. This procedure may be extended for developing bloody fingerprints. The blood protein is denatured and fixed on the surface by baking the sample in an oven at 100º C for about 5 minutes. Thereafter, the prints are sprayed with ninhydrin, followed by zinc chloride treatment and then examined under laser. 6. Summary Blood-fingerprints are often found at violent crime scenes. These may be detected by a legion of chemical methods. The detection methods are broadly classified into two categories: Those which tag the heme content of blood-smeared crime scene evidence and those which tag the protein content of coated blood. However, no single technique has universal application under all circumstances for the development of Blood prints. Research efforts have focused on methodologies that may be applied to difficult and unusual surfaces. The method choice thus varies from case to case.