A methods for detecting and identifying fingerprints

Methods for detection and identification of traces of hands are divided into visual, physical and chemical.

A methods for detecting and identifying fingerprints

a) visual observations made with the naked eye, using equipment and increase the use of different means and methods of illumination.

Visually detected painted, depressed, surface traces, layering and peeling, discolored potozhirovye marks on glossy transparent and opaque objects.

Thus a significant role illumination methods most typical of these are based on the use of artificial light sources.

With the use of special light sources (e.g., ultraviolet illuminator laser) can be observed and invisible trace.

b) Physical methods are based on the ability of certain substances over time to maintain the pressure adhesion, and the possibility of selective adsorption of excite luminescence.

About 40% of all forensic examinations constitute expert studies traces of hands that are most often found at the crime scene investigation. Colorless potozhirovye traces remain on the surface of objects, usually at the touch of any fingers. However, it is not always such traces are clearly visible and not in all cases, they can be made visible by means of existing technical and forensic tools.

The most common way to detect traces of colorless hand pollination is their powders. This method is simple, does not require a complicated apparatus is applicable in almost any environment and in many cases give effective results.

Let us dwell on the application of powders in detecting traces of hands on different surfaces, we present characteristics sledovosprinimayuschih surfaces, consider their influence on the ability to identify traces of hands powders, as well as methods for preparing surfaces before using powders, methods of their application, especially to identify traces of hands using powders various surfaces.

Formation potozhirovyh traces of hands and the ability to identify powders are largely dependent on the properties of the surface sledovosprinimayuschey, mainly from its relief and the ability to absorb moisture. The smaller the surface topography, the more it is smooth, the more accurately reflect the details of the structure of fingerprint images. Therefore, for the formation of traces of hands potozhirovyh most favorable surface are close to the mirror glass, lacquered wood, etc. On rough surfaces details fingerprint appear worse or do not appear if the value of the individual points of the surface relief is greater than the height of the ridges of papillary lines.

On absorbent surfaces potozhirovoe substance rapidly penetrates and traces a short time turned into a blur, not showing the details of the structure of the papillary patterns. This surface has the most varieties of paper, cardboard, leather, fabric and others. Usually these surfaces colorless fingerprints difficult to identify powders had a few hours after their abandonment.

Penetration Time sledoobrazuyuschego substance subject material depends on the capillary properties of the material and the ratio of basic components potozhirovogo substance, particularly with a large number of traces of sweat absorbed much faster.

On surfaces, does not absorb moisture (glass, porcelain, earthenware, plastic and others.), Traces of papillary patterns can be stored and identified the powder through a very long time – a month or more.

The formation of traces of hands and the ability to identify powders affect not only inherent properties of the surface of the object, but also the conditions under which it was from its inception to its trace detection: temperature, humidity, dust.

Elevated temperature and humidity in the reduction period leads to intense distortion components sledoobrazuyuschego liquid substances, fat and oxygen under the influence of heat oxidized. These processes lead to the fact that with time sledoobrazuyuschee substance turns into a thin hard film, which does not adhere to the powder particles. These should be identified very difficult.

Effect of water on potozhirovye traces depends on what components predominate in sledoobrazuyuschem substance. Fat traces can be stored for a long time under water, and after drying the surface detected powders. Those traces that are predominantly components of sweat, water can be destroyed within a few minutes.

Settled on potozhirovye traces of dust prevents contact with the powder particles sledoobrazuyuschim material and thus hampers their manifestation.

Sometimes the ability to detect traces of powders depends on the physico-chemical properties of the surface material. For example, the surface of polished metals poorly wetted fatty acids that make up a sweat, which is localized on these small droplets evaporates quickly and does not form a clear trace, identifiable powders.

Preparation of the surface on which you want to search traces of hands, largely determines the possibility of identifying powders. First of all, it is necessary to determine the surface material (glass, metal, plastic, etc.) in order to apply the corresponding powder. To search for traces need to inspect the surface from different angles and in different light. In addition to conventional lighting, you can use blue, yellow or ultraviolet light, which in some cases can increase the contrast of the traces of hands regarding sledovosprinimayuschey surface.

Because the processing of powder in some extent distorts the structure of the display fingerprint, items which were found during the inspection colorless subtle traces of fingers, no need to pollinate powders, traces should be photographed on the spot or to take the subject for photography tracks in the laboratory. Only after photographing footprints can be processed powders that enhance their contrast.

To clean traces of dust, can be directed air flow from the fan or blower on the surface of the object, or dust off lightly brush pile fingerprint. Old, dried up marks on smooth surfaces before processing powders need to “refresh” humidification: breathe in the areas where such traces are assumed. Typically the surface on which the trace, the exhaled air is colder and moisture contained in the breath, condensed into a spot. Moisten a few times, so the surface and waiting for the disappearance of spots condensate, you can begin to manifest traces.

Wet objects on which it is assumed the presence of traces of hands should be dried; cold or icy objects need to be made into a warm room (humid), and the resulting water droplets on them to remove the filter paper or a jet of air. Objects absorbent (paper, cardboard, wood uncolored) must be dried in a drying cabinet or room at a temperature not exceeding 25 ° C.

If the item is broken or broken, you need to restore its integrity, while respecting the necessary caution.

When painting traces of hands powders should be guided by the following general rules:
– Powders must be finely divided (dustlike); vary in color from the surface on which may be traces; have good adhesion (adhesion) to the next and does not stain the surface on which they are located; retain color and crisp detail on the track fingerprint sledokopirovalnoy film;
– It is advisable to first choose the appropriate method of applying the present case powder and pre-paint the experimental traces on the same or similar surface;
– Can not be applied to wet powders, dirty or sticky surface. It should be dry and free from contamination. (To detect traces of hands on the sticky surface application of powders are not recommended to be applied iodine vapor or liquid chemicals);
– On smooth surfaces should be used for smaller structure powders on rough – larger;
– If not revealed traces of a powder, it is possible to use other, more sticky or heavy, or a mixture of powders.

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