latent print fingerprint classification. they are permanent they are unique
Post on 18-Dec-2015
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- Latent Print Fingerprint Classification
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- They are permanent They are unique
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- Latent - The skin has deposits of oil and perspiration that normally coat its surface. When the hand touches the surface, some of the moisture is transferred from the hand to the object, leaving an impression of the friction ridge detail. These are referred to as latent impressions.
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- On most surfaces latent impressions are not readily visible. The word latent is defined as not visible to the naked eye. That does not mean that the latent print is actually invisible. On most surfaces, the impression will be revealed through the use of available or oblique lighting. The impression must be enhanced or developed to be collected and seen completely.
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- Patent A patent impression occurs as the result of transferring a foreign material coating to the skin of the fingers. Examples of the foreign material would be substances like paint, tar, grease, blood, or ink.
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- The best example of a patent impression would be the ink standards or eliminations that we, as investigators collect from individuals. After the ink is applied, it becomes foreign material coating the hands of the individual. A card is used as a transfer medium, thus becoming the object touched and the transference of the patent impression takes place.
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- The word patent means obvious or evident. Patent impressions are visible and usually need no enhancement. They are simply photographed and the item that they are deposited on is collected if necessary. The photograph or object actually becomes the investigators lift.
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- A plastic or molded impression is deposited when the hands, fingers, or feet are pressed into a soft, rubbery type material that will retain the impression of the ridge detail.
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- The difference between a latent and a plastic or molded print - Where a latent impression is deposited on the surface, a plastic or molded impression would be deposited into the surface. Examples of the materials where a plastic or molded impression would be deposited are clay, wet paint, blood, or tar.
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- Plastic or molded impressions are visible and usually need no enhancement. They are simply photographed and if necessary, the item is collected and may have the ability to be casted.
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- Alternative Light Source Chemicals Powders
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- Perspiration contains elements that fluoresce when illuminated by laser light. Fluorescence luminescence that is caused by the absorption of radiation at one wavelength followed by nearly immediate radiation usually at a different wavelength that ceases almost at once when the incident radiation stops
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- Relatively inexpensive and versatile Comparable results can be attained by modified and filtered xenon arc lamp to those of laser light sources
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- Iodine Fuming this is the oldest method for visualizing latent prints Iodine, a solid crystal, is heated and transformed into a vapor. This is known as sublimination. The suspect material is put into an enclosed cabinet known as a fuming cabinet.
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- The iodine crystals are heated and the vapors fill the chamber and combine with the latent print to make it visible. In order to have a permanent record of the latent prints, the prints must then be photographed immediately or fixed with a 1% solution of starch and water that is sprayed on; for they will fade once the fuming process is stopped.
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- The amino acids present in perspiration chemically react to ninhydrin forming a purple- blue color. Ninhydrin is sprayed onto the porous surface containing the latent prints. Within an hour or two the prints begin to appear. This method has been used on paper up to fifteen years old. Ninhydrin is often the preferred method because of it is extremely sensitive and easy to apply.
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- This method of visualizing latent prints is used on nonporous surfaces such as metals, electrical tape, leather, and plastic bags. Cyanoacrylate ester interacts with and visualizes a latent fingerprint. Super Glue is placed on an absorbent cotton treated with sodium hydroxide. (The glue may also be heated to create fumes.)
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- The object and the super glue are both enclosed in the fuming tank for thirty minutes to an hour. Sometimes a latent print can be placed on a black card. This is placed in the tank for development of the print. This can be used as an indicator for other items in the fuming cabinet.
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- When the fumes from the glue adhere to the latent print, the print often appears white. Super Glue fuming may now be done using a small portable unit consisting of a handheld wand. This wand is used to hold a small cartridge of Cyanoacrylate and dye mix, which is applied to any areas where latent prints are assumed to be present.
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- Latents can be dusted with various colored powders to increase their visibility. Gray and black powders are sufficient for most latent print work. The examiner will use the powder that will result in the most contrast. These powders are applied via camels hair or fiberglass brushes.
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- Magnetic-sensitive powders may also be used. A magnetic brush is used to spread the powder over the surface. The magnetic-sensitive powder is especially useful on plastics and leather. Fluorescent powders are sometimes used. The print becomes visible under ultraviolet light.
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- These methods must be done in a specific order if you wish to use multiple methods on one surface. First fume with iodine. Then use ninhydrin.
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- Fingerprints may be placed into three general groups of patterns, each group bearing the same general characteristics or family resemblance. Loops 65% of all fingerprints Arches 5% of all fingerprints Whorls 30% of all fingerprints
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- Pattern Area is that part of a loop or whorl in which appear the cores, deltas, and ridges with which we are concerned in classifying. The pattern areas of loops and whorls are enclosed by type lines.
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- A fingerprint core is an area located within the inner most recurving ridge.
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- A delta is that point on a ridge at or nearest to the point of divergence of two type lines, and located at or directly in front of the point of divergence.
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- Type Lines may be defined as the two innermost ridges, which start parallel, diverge, and surround or tend to surround the pattern area. Type lines are not always two continuous ridges. They most often are found to be broken, and sometimes they may be very short. Care must be exercised in their location.
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- A loop is that type of fingerprint pattern in which one or more of the ridges enter on either side of the impression, recurve, touch or pass an imaginary line drawn from the delta to the core, and terminate or tend to terminate on or toward the same side of the impression from whence such ridge or ridges entered.
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- A sufficient recurve may be defined as that part of a recurving ridge between the shoulders of a loop. It must be free of any appendages abutting upon the outside of the recurve at a right angle. Appendage defined - a ridge abutting an otherwise smoothly recurving ridge A delta A ridge count across a looping ridge
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- In plain arches, the ridges enter on one side of the impression and flow or tend to flow out the other with a rise or wave in the center. This is considered the most simple of all fingerprint patterns to recognize.
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- A tented arch may resemble a loop, but lacks one of the characteristics of a loop A tented arch possesses either an angle, an up thrust, or two of the three basic characteristics of the loop
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- The Plain Whorl The Central Pocket Loop Whorl The Double Loop Whorl The Accidental Whorl
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- Plain WhorlCentral Pocket Loop Whorl Double Loop WhorlAccidental Whorl
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- The plain whorl has two deltas and at least one ridge making a complete circuit. An imaginary line drawn between the two deltas must touch or cross at least on of the recurving ridges within the inner pattern area. A recurving ridge, however, which has an appendage connected with it in the line of flow cannot be construed as a circuit. An appendage connected at that point is considered to spoil the recurve on that side.
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- The central pocket loop whorl has two deltas and at least one ridge, which makes (or tends to make) a complete circuit. An imaginary line drawn between the two deltas must not touch or cross any of the recurving ridges within the pattern area.
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