Physical amp Chemical Techniques Latent Print Latent means hidden and the prints must be developed to make them usable and identifiable A chance impression caused by perspiration through the sweat pores on the friction ridges of the skin being transferred to another surface ID: 1037562
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1. Development of Latent PrintsPhysical & Chemical Techniques
2. Latent PrintLatent means hidden, and the prints must be developed to make them usable and identifiable.A chance impression caused by perspiration through the sweat pores on the friction ridges of the skin being transferred to another surface.Three things must be present for a quality latent print to be deposited, a sufficient transfer medium, a suitable substrate or surface, and appropriate handling of the object. Latent fingerprint development may be achieved with a wide array of optical, physical, and chemical processes
3. Conditions Affecting Latent Prints
4. Surface TypesSEMIPOROUS
5. The Crime Scene Search and Fingerprint Development
6. Working of ALS
7. PHYSICAL TECHNIQUES / LATENT PRINT POWDERS
8. Latent Print PowdersApplication of finely divided particles that physically adhere to the aqueous and oily components in latent print residue on nonporous surfaces.Fingerprint dusting relies on the adherence of powder (Mechanical attraction) to moisture and oily components of the latent print residue to provide good visibility and definition of fingerprint detail. Powdering is not recommended for porous or highly absorbent surfaces such as uncoated paper or raw wood.
9. Latent Print PowdersTwo essential elementsPigment –Provides for effective visualization, offering contrast and definition against the background surface.Particles that serve as good fingerprint powders include carbon black (colloidal carbon), lamp black, talc, kaolin, aluminum, metal flake, and dolomiteBinder/carrierProvides for maximum and preferential adhesion to latent print residue.Good binders include iron powder, corn starch, rosin, and gum Arabic.
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11. Latent Print Powders : Magnetic or magna powderAllows for application with a magnetized rod that has no bristles.This type of powder can be light, dark, or fluorescent and utilizes the ferromagnetic properties of iron powder mixed with pigment powders. The magnetized applicator (magna brush) is dipped into the powder, picking up a ball of the iron and particle mixture, essentially forming its own Causes less damage to fragile latent prints.Magnetic powders are usually less effective on ferromagnetic substrates such as steel or nickel and are therefore not recommended on those substrates. The magnetic attraction may cause contact between the applicator and substrate, damaging latent prints in the process. In addition, magnetized particles from the powder will cling to the substrate and resist removal
12. Latent Print Powders : Fluorescent powderRelies on the principle of luminescence to provide contrast between fingerprint and background.Fluorescent powders are typically created by adding a laser dye in solution to a binder and allowing the mixture to evaporate. The resulting dried mass is then ground into latent print powder.Advantage Less activity is required to develop latent prints, thus lessening the likelihood of destruction of the print. DisadvantageAdditional luminescence is required in the form of an alternate light source (ALS) or light amplification by stimulated emission of radiation (laser) to make the print usable.
13. CHEMICAL TECHNIQUES
14. NinhydrinNinhydrin was first described in 1910 when Siegfried Ruhemann mistakenly prepared the compound.Ruhemann observed that the new compound reacted with skin and amino acids to produce a purple product.
15. NinhydrinSweat Residue contain a small, but detectable, amount of amino acids, averaging about 250 ng per fingerprint. After the water evaporates from the surface, the amino acids remain as solid material.Ninhydrin reacts with the amino acids, peptides, and protein contained in the print.This technique can by applied by : spray, swabbing, or dipping method.This chemical is used on items such as paper, cardboard, and unfinished wood.The desired temperature is approximately 80°C, with a humidity rate of approximately 80 percent.
16. Post treatment of Prints developed by NinhydrinThe UV-to-visible light spectrum : λ = 407 nm and λ = 582 nmTreatment with zinc chloride and using the light of an argon ion laser.Post treatment with metal salts:zinc, cadmium, cobalt, and copperFormation of a metal-salt complex alters the color of Ruhemann’s purple from deep violet to red or orange, depending upon the salt used.Post-treated fingerprints may be further enhanced by viewing under 490 nm light (for zinc-treated residues) or 510 nm light (for cadmium-treated residues)
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18. Ninhydrin Analogues- DFO1,8-Diazafluoren-9-oneBest used through dipping or swabbing the piece of evidence.ALS or laser is required for visualization.The reaction is with amino acids, peptides, and protein contained in the print.The product of this reaction is pink to red in color with λmax of approximately 560 nm and a weaker absorption at 520 nmUnlike the ninhydrin reaction, the DFO reaction requires a high-temperature, low-humidity environment.More sensitive fingerprint development reagent than ninhydrin.
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20. Iodine FumingIodine is absorbed by the fingerprint secretion, which produces a dark brownish to blackish appearance.Iodine interacts with Fatty acids and lipids contained in the fingerprint.Tend to work on relatively fresh prints.Technique is used for paper and may be used on human skin.resulting prints that develop must be photographed as the prints tend to fade over timeMethod of application: Fuming gun, Fuming Cabinet,
21. Developed print fades over timeLab set up for Iodine fuming
22. Cyanoacrylate EsterReacts with the amino acids and fatty acids in the perspiration to form a white colored polymer.Suitable for metal, glass, plastic, garbage bags, electrical tape, and many other nonporous surfaces.Method of Application: Fuming chamber & CAE wandEnhancement : Variety of powders or dye stains can be used along with ALS or laser.Disadvantage : May aggravate the mucous glands and membranes.
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24. a) Fresh Fingerprint on stainless steelb) Old Fingerprint on stainless steelc) Fresh Fingerprint on Aluminum Surfaced) Old Fingerprint on Aluminum Surface
25. Sticky-side powder/ Gentian Violet (Crystal Violet)Used to develop prints on the adhesive side of tape. Gentian violet is used by dipping the item into a bath of the material. Sticky Side Powder may also be used in a bath, or by painting the adhesive surface. The specimen to be treated is simply immersed in or floated on a 0.1% w/v aqueous solution of gentian violet for one to two minutes and then rinsed with water. Repeated stain/rinse cycles may be used to intensify the color of the stains.With some types of tape a clearing solution of 1 M hydrochloric acid is used as the final rinse, to remove background staining without affecting the developed prints.
26. Small Particle Reagent A suspension Small particle reagent (SPR) technique is an effective method to develop latent fingermarks on moist, non porous surfaces. The method is based on the adherence of fine particles of treating solution to the oily or fatty components of latent fingermark residues.Consists of a suspension of fine molybdenum disulfide particles in an aqueous medium containing detergent solution (as surfactant).The gray, shiny prints that are developed with SPR can be lifted (after drying) with Gel lifters, Instant Lifters or tape.
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28. Analogs That React with Blood
29. Procedure After Developing Prints