The search for handprints is largely determined by the nature and context of the event. When inspecting a closed crime scene (apartment, garage, house, etc.), first of all, pay attention to the surfaces that the criminal could touch while entering the premises, being in it and leaving it.
When working with hand marks, the following must be observed: general recommendations.
Before detecting handprints, it is necessary to take measures so that during the search not to destroy other traces present on objects and not to complicate their further research (shoe marks on the floor, microfibers on a window frame, traces of biological origin, etc.).
Objects that may contain traces must be taken in such a way as not to leave your own traces and not damage the traces of the criminal.
To identify traces, it is first necessary to use visual detection methods, and then physical or chemical ones.
First of all, traces are detected on objects that may be exposed to atmospheric precipitation, thermal effects, mechanical damage, etc. When moving objects with hand marks, sudden changes in temperature must be avoided.
In investigative and expert practice there are various ways detection of hand traces: visual, physical and chemical.
Visual (optical) methods used to detect voluminous, colored or barely visible traces. These methods are based on enhancing contrast by creating favorable conditions lighting and surveillance.
These methods include: examining objects with the “naked eye” from various viewing angles or holding transparent objects to light, or using optical magnification devices (magnifying glass, microscope), lighting devices (lamps, lanterns), as well as using a laser, sources of ultraviolet rays, light filters.
The advantages of the listed methods are simplicity, accessibility and rationality, since they do not lead to disruption of either traces or surfaces of perceiving objects and therefore should be used in the first place.
Physical methods based on the adhesive (attractive) or adsorption (absorbing) properties of the trace-forming substance. In the first case, coloring of the trace occurs due to the deposition of tiny particles of dye on the substance, in the second - due to their introduction into the trace substance without chemical reaction. Such methods include the following.
Use (pollination) of fingerprint powders. This method consists of mechanically painting the surfaces of objects with powders that differ: in structure (fine, coarse), in specific gravity(light and heavy), by color (light, dark, neutral), by magnetism (magnetic and non-magnetic), by composition (single-component and mixtures, fluorescent and phosphorescent).
When working with powders, you must comply following conditions: the surface of the object to be treated with powder must be dry and not sticky; The powders must be dry and fine, contrasting with the surface being treated. All powders are used to detect fresh handprints.
Powders are applied to the surface of the trace-receiving object in one of several ways: a) bulk (rolling the powder over the surface of the object under study); b) using a nap brush - a flute brush, a fiberglass brush or a magnetic brush; c) using aerosol sprays, “air mills”.
Fumigation with iodine vapor. The impact on the trace-receiving surface is carried out by spraying crystalline iodine. Dignity this method is that traces can be processed several times. Disadvantage - traces quickly disappear and become invisible. Iodine vapor is obtained using an iodine tube with a rubber bulb. The identified traces are fixed with iron powder reduced with hydrogen. Iodine vapor is used to search for more recent (old) traces, as well as on objects (objects) on which the use of powders is undesirable.
End of the trail used to detect hand marks on polished surfaces. Its essence is as follows: when individual objects are burned (for example, casts made using paste “K”, polystyrene foam, camphor, naphthalene, pine splinters, etc.), soot is released abundantly, which is a fine powder, which colors the sweat and fat hand mark.
Chemical methods detection (detection) of invisible handprints is based on the ability of individual substances to react with the components of sweat and fat secretion and ultimately color it in one color or another. These methods are used to detect handprints on paper, cardboard, and unpainted wood of various ages (in some cases up to several years) and are usually used in laboratory conditions. Apply the solution to the surface using a spray bottle or a cotton-gauze swab. The following chemical reagents are used: silver nitrate, ninhydrin, alloxan, benzidine, etc.
Silver nitrate (lapis) has the form of colorless crystals. A 1-2% solution of silver nitrate is prepared in distilled water and the object with traces is treated using a cotton swab or spray bottle. The item is then dried in the dark and exposed to bright light or ultraviolet rays. Silver nitrate reacts with chloride salts that are part of the fat secretion, and silver chloride is obtained, which darkens in the light.
Ninhydrin. White or pink powder, poisonous. A 0.1-0.8% solution of ninhydrin in acetone is used and applied in a similar way. Ninhydrin is one of the most sensitive reagents for amino acids and other protein compounds. The process of identifying traces lasts several hours; to speed up the process, the object should be heated (ironed with an iron, placed on a radiator). Identified traces are colored blue purple.
Alloxan. A 1-1.5% solution of alloxan in acetone or alcohol is used. The traces are colored orange and have a bright crimson glow in ultraviolet rays. Traces appear in a time from 2 hours to 1-2 days.
A solution of benzidine in alcohol with hydrogen peroxide (five parts of a 0.1% solution of benzidine in alcohol and one part of 3% hydrogen peroxide) is used to detect hand marks formed by a layer of blood. Blood marks treated with this solution turn blue-green. The coloring is stable and does not require additional fixing.
Handprints found (identified) at the scene of the incident must be recorded. The main method of recording is the description of traces in the protocol of inspection of the scene of the incident, additional methods are photography; drawing up schematic sketches, diagrams, plans; fixing a trace on an object; trace copying.
In the most general view the description of hand marks in the protocol can be carried out according to the following scheme: characteristics of the object on which the marks were found, its name, location, condition of the object itself and its surface; individual characteristics of the item (number, marking); method of identifying traces, quantity, shape, size, location on an object and relative position; the type of each trace (superficial, volumetric, sweat-fat - barely visible, invisible, if painted, then its color); type of papillary pattern (whorl, loop, arc); whether the traces were processed, if so, how; whether handprints were photographed; methods of removing a trace (item), color and size of the trace-copying film on which the traces were seized; how the trace was packaged (characteristics of the material), the content of the inscription on the package and what seal it was sealed with.
If possible, an object with traces of hands confiscated in kind and if it is impossible to do this, the traces are recorded by copying, i.e. transferring them to trace-copying film. Depending on the color of the powder used to identify traces, a special trace-copying black (for light powders) or transparent film (for black powders) is used. It consists of two sheets of celluloid, one of which (the main one) has a copying mass applied to it. The other sheet is protective; it protects the copy material from drying out when storing the film; After copying the trace, the protective layer is again applied to the main one and protects the copy from damage.
Photography hand traces at the scene of the incident are carried out with a Zenit type SLR camera with extension rings.
Direct fixation of traces on the object is carried out using aerosols (hairspray, etc.); traces treated with iodine vapor, as noted above, are fixed with iron powder reduced with hydrogen.
Contact copying of traces is carried out on: dacteal film; sticky tapes; fixed soaked photographic paper; medical adhesive plaster; insulating tape; vulcanized rubber; polymer materials(trace copying tool "Copy"); traces treated with iodine vapor can be copied onto self-coloring film or paper.
Making casts from volumetric handprints is carried out using various synthetic materials(crust, solutions, mixtures).
Forensic examination of handprints is usually called fingerprinting (from the Greek. (- finger and - look; lit.: finger examination). The subject of this examination is to identify the person who left the trace at the scene of the incident, as well as the time and conditions of the trace formation.
For a fingerprint examination for the purpose of identifying a person, you should send an object with a trace or a fingerprint film with its imprint, a photograph, a report of an inspection of the scene of an incident or other investigative action during which traces were found, as well as a fingerprint card of the suspect or other persons who could have left handprints at the scene incidents.
The expert may be asked the following questions:
- o Are there handprints on the presented object and are they suitable for identification?
- o Are the handprints left by a specific person?
- o Which hand - right or left - or which fingers of which hand left the discovered traces?
- o What actions (touching, grabbing, etc.) left marks?
- o Are traces left in different places by the same person, etc.
Physical detection methods.
1. Detection of handprints using fingerprint powders.
Types of powders:
1) light - zinc oxide, aluminum, lead oxide, lycopodium, titanium oxide, magnetic powders "Opal", "Topaz", etc.;
2) dark - copper oxide, graphite, soot, magnetic powders "Ruby", "Agate". "Sapphire", "Malachite", etc.; G
3) neutral - carbonyl iron, etc.
Powder quality requirements:
powders must be finely dispersed (dusty);
differ in color from the surface on which marks may be located;
have good adhesion (stick to marks) and do not paint the surface being treated;
preserved in the trace, including those copied onto fingerprint film, unchanged.
Powder application methods: fingerprint brush (kolin, hare or lavsan) brush; magnetic brush (except unpainted metal objects having magnetic properties); rolling the powder over a surface (paper, cardboard, as well as small flat objects). Using an air spray on rough or large surfaces, followed by “re-developing” the marks with a fingerprint brush.
Rules for identifying traces with powders: Before processing with fingerprint powders, the material from which it is made (metal, plastic, wood, etc.) is determined. Then its surfaces are examined at different angles to the light source. To increase the contrast of handprints, along with conventional lighting, illuminators with blue, yellow or ultraviolet rays are used. Inconspicuous, colorless fingerprints are photographed before pollination with powders, and old fingerprints are moistened with breath before processing. Wet items are dried, and icy items are brought into the room to be thawed before treatment. Drops of water are removed with filtered paper or a stream of air. The powder should be selected not by color, but by its ability to clearly show a mark on a given surface. When hand marks appear on the surface being treated, their further development or cleaning of excess powder is carried out by directing the brush longitudinally to the main flows of papillary lines.
fingerprint papillary pattern hand
2. Detection of hand marks using iodine vapor
Iodine vapor is absorbed by the fatty substance. With the help of iodine, traces are detected on paper, glass, metal, wood, plastic, as well as on fibrous, non-glossy surfaces. Iodine vapor is one of the highest quality and most reliable means of detecting fingerprints.
Used for vapor sublimation various means and ways:
The simplest method is in which iodine crystals are placed in glass jar. The neck of the jar is covered with an object with supposed traces or it is lowered inside the jar, while closing it with a lid. The jar is heated. Iodine vapor stains traces of Brown color; sublimation of iodine vapor using an iodine tube. She represents glass tube with taps at the ends, in the middle part of which iodine crystals are placed. The ends of the tube near the chamber are covered with glass wool. At one end there is a hose from a rubber bulb, equipped with a valve for one-way air circulation.
Direction of movement of the fingerprint brush:
A - arbitrary, used to identify handprints;
B - ordered, used to remove excess powder and improve the quality of the mark.
Iodine tube.
1 - spray bulb; 2 - connecting hose; 3 - input valve; 4 - glass wool; 5 - iodine crystals; 6 - output valve; 7 - tube nozzle.
During operation, the tube is heated by the heat of the hand, iodine vapor is released from the tube using air supplied by the bulb and directed to the surface where hand marks are supposed to be present. Traces revealed by iodine vapor are fixed with iron powder reduced in hydrogen. To increase the contrast when taking photographs, traces must be constantly smoked in pairs or a blue (blue) color filter must be used. After operation, the tube taps are tightly closed.
3. Detection of handprints using the digging method
For smoking, substances are used that produce fine-structured soot when burned: naphthalene, camphor, polystyrene foam, pine splinter, etc.
The object is moved over a smoky flame until its surface is covered with soot. Excess soot is removed with a fingerprint brush.
The best effect of identifying traces using the pickling method is achieved on polished metal surfaces, marble, plastic, glass, and porcelain.
4. Detection of hand marks using the drug "Tkanol".
The drug "Tkanol" is used to detect handprints on fine-textured fabrics. It consists of 1 part crushed crystalline iodine and 10 parts starch. Iodine and starch are mixed in a container with distilled water (to the consistency of thick sour cream). The solution is evaporated and the mass is crushed in a mortar to a powder. Traces are revealed by rolling the powder over the surface being treated, and shake off the excess.
5. Detection of handprints using radioactive isotopes (autoradiography)
This method reveals old marks on paper or cardboard. There are several ways to treat traces with radioactive materials. The simplest and safest method is based on the adsorption of stearic acid labeled with radioactive carbon by the fatty substance. In this case, the item will be stored for 10 minutes. placed in a 0.1% benzene solution of stearic acid labeled with radioactive carbon. Then it is removed from the solution and for 10 minutes. kept at a temperature of +80° C. To remove labeled carbon atoms from the background, the object is dipped in pure benzene, then dried and placed in a cassette in contact with x-ray film.
Another method is to use formaldehyde labeled with radioactive carbon. To do this, the object is placed in a plastic or glass vessel, at the bottom of which there is a cuvette with an aqueous solution of formaldehyde labeled with radioactive carbon C-14. The infection process lasts at room temperature for 10 - 20 minutes, after which the trace becomes radioactive and upon contact with photographic film leaves an image on it.
6. Detection of handprints using optical quantum generators (lasers)
The most suitable for detecting handprints are lasers with blue-green radiation - argon lasers.
The object of study is illuminated with a beam of an argon laser type LG-503 or PDSP "Lazex-1": in the presence of a sufficient amount of riboflavin in the composition of the sweat-fat substance, the trace luminesces in this spectral range. For safety during research, it is necessary to use glasses with safety filters that block light waves with the length of laser radiation and transmit luminescence waves with a length of more than 540 nm greenish-yellow or orange color.
Identification and photography are carried out in a darkened room. When photographing, the same barrier filters are used as during detection. The color contrast can be increased by treating the trace with certain substances (ninhydrin, alloxan) or luminescent materials (rhodamine, fluorescamine, etc.).
Since this method is non-contact, other detection methods can be used before and after it when the use of traditional methods is ineffective.
7. Thermal vacuum spraying method
The essence of the method: metal powder is heated until it evaporates under high vacuum conditions, metal atoms selectively condense on the surface of the object. Due to the contrast that arises between the color of the background and the traces, the latter become visible.
The device consists of a transparent cap with an evaporating device from which air is pumped out, a vacuum pump and a control unit. Metals (zinc, antimony, copper, gold, cadmium, etc.) and their mixtures are used for evaporation.
For example, for one spraying it is required: silver - 2 mg, zinc - 10 mg. The basket with silver is heated to the temperature of a blue-white glow, then the current passing through the basket with zinc is increased to the temperature of a dark red glow. Evaporation of zinc continues for 2-4 minutes. The development process is controlled visually.
The method is more effective in detecting handprints on the surface of paper, cardboard, unpainted wood, some plastics and polyethylene films. It is possible to identify traces of considerable age (up to two years). In terms of trace clarity and contrast, it surpasses traditional methods. Disadvantages of the method: inability to process large items; the device is brought into working condition for a long time (pumping out air takes a lot of time); It is necessary to select the evaporated metal in contrast to the color of the surface being treated.
8. Electrolytic method for identifying and fixing traces of sweat and fat on metal surfaces
The electrolyte is an aqueous solution of salts of a certain metal (for example, silver in distilled water). The concentration of the solution should be 4 - 10%. The power source can be three batteries for a household flashlight connected in series. Development and fixation time is 3 - 5 minutes. The quality of displaying traces is high, right down to the fixation of pores.
The container is filled with electrolyte, an object with traces is placed in it and connected to the minus pole. The plate with the plus pole will also be placed in the electrolyte. The distance between them in the electrolyte is from 5 to 10 mm. After the traces are developed, the object is washed in running water.
Chemical methods for identifying fingerprints
The methods are based on the reaction of sweat fat components and reagents, which causes staining of hand marks. The following are used chemical substances: ninhydrin, alloxan, silver nitrate solution, benzidine, leucomalachite green solutions, cyanoacrylate.
1. Ninhydrin is a white crystalline powder, highly soluble in water, acetone, and alcohol. Reacts with amino acids, turning traces a range of pinkish-purple colors.
A 0.2 - 2% solution of ninhydrin is used, which is applied to the surface using a spray bottle, a cotton swab, or by bathing the object examined in the solution located in the cuvette. The appearance of traces is recorded visually after 20 - 30 minutes. As the temperature increases, the staining of traces accelerates. For this you can use a drying cabinet, iron, battery central heating, hot steam, etc. The quality of manifestation (precision of traces) largely depends on the content of the amount of amino acid in the sweat-fat substance.
This method reveals traces of great age on paper, plywood, and planed wood. Traces are not detected on varnished, polished, painted wood, plastic, as well as on surfaces with a fatty base. After treatment with ninhydrin, silver nitrate can be used to identify traces.
To slow down the reaction of ninhydrin with amino acids (with low contrast between trace and background), a 1.5% solution of copper nitrate in acetone is used. Traces found on securities and banknotes can be discolored with a 15% hydrogen peroxide solution.
2. Alloxan- white crystalline powder or Pink colour, dissolves in water, alcohol, acetone. When heated, it turns orange. Reacts with protein breakdown products and colors them.
A 1 - 2% solution of alloxan in acetone is used. To identify traces that are older, a 10% alloxan solution is used.
The identified traces fluoresce in ultraviolet rays. Traces treated with alloxan appear after 2 - 3 hours and are orange in color. The object with identified traces is placed in a place protected from light. A painted background, for example, on paper that does not have sizing (newspaper, wrapping paper, etc.), can be weakened with a 1.5% solution of copper nitrate in acetone, acidified with 2 drops of 10% nitric acid.
Weakly colored traces can be further enhanced by ninhydrin, which acts on other components of the sweat fat substance.
3. Silver nitrate ( 5 - 10% aqueous solution) is used to detect traces on paper, cardboard, plywood, and unpainted wood. The treated item is placed in dark place, then exposed to light. The chloride compounds that make up the sweat-fat substance turn black after a few hours when exposed to light. As a rule, silver nitrate detects traces up to six months old
4. Benzidine (0.1% solution in alcohol) and hydrogen peroxide (3% solution) are used to detect faint and invisible hand marks left by blood.
The solution is made up of 0.1 g of benzidine in 100 ml of alcohol. To 5 parts of this solution add 1 part of a 3% hydrogen peroxide solution. The last component is mixed immediately before detection.
5. Detection of sweat and fat traces of papillary lines using cyanoacrylate vapor.
Cyanoacrylate is used to detect invisible handprints in confined spaces. The action is based on the reaction of the sweat-fat substance with amino acids and water, which causes the polymerization process, coloring the trace white and fixing it on the surface of the object.
For this technique you can use different kinds glue created on the basis of a-cyanoacrylic acid with the brand "Ciacrine".
To identify traces, the object is placed in a closed space (chamber), preferably with transparent walls. Depending on the size of this chamber, add a few drops of cyacrine (from one to several dozen), for example, for a 200 ml container - 1-2 drops, 10 liters - 30-40 drops. At room temperature (19 - 21°C), vaporization occurs and polymerization begins in the trace area. The duration of complete polymerization is from 12 to 24 hours. Cyanoacrylate polymerizes on the mark, increasing its mass and making it more prominent.
When heated to 60 - 70°C, steam formation occurs more intensely, within 15 - 20 minutes.
Good results in identifying and simultaneously fixing traces are obtained on glass, plastic, metal surfaces, worse on polyethylene, linoleum, porous rubber, and paper. Results are better with slow steaming conditions room temperature or with gentle heating.
To simultaneously detect traces on the internal and external surfaces of some devices and objects, cyacrine is used in a thermal vacuum installation. For example, when processing a pistol, traces of sweat and grease will be revealed (if they are present on the surface of cartridges, magazines and other parts.
6. I use potassium permanganate in an aqueous solution with sulfuric acid; to identify traces on polyethylene.
For 1.5 liters of water use 15 g of potassium permanganate with the addition of 10 ml of sulfuric acid.
The object is placed for 10 - 30 s in the prepared solution, the degree of detection is observed visually. The traces are painted in a persistent dark brown color. After removing the object from the solution, wash it in cool water.
Fixation methods
Traces found at the scene of an incident can be recorded: by describing them in the protocol for the inspection of the scene, photographing, directly attaching to an object and copying.
When describing the traces in the protocol for the inspection of the scene of the incident, the following must be indicated:
the object on which traces were found, its location, description ( features), the nature and color of the surface of the object;
the method of identifying traces, their type, quantity, shape, size, location on the object and relative position;
techniques and means used by a specialist to identify traces.
The choice of tools and techniques recommended by forensic science for searching for handprints at a crime scene largely depends on the type of traces left behind. In practice, there are volumetric and superficial traces of human hands. Volumetric traces are formed on soft material due to its residual deformation, for example on clay, some withanium products, etc. Finding such traces is not particularly difficult; they are found when visual inspection conditions of the scene of the incident. For better perception, it is recommended to use oblique lighting. It is advisable to remove voluminous handprints along with the object on which they are located. If this cannot be done, casts are made from the marks. It must be remembered that before making casts, the traces should be photographed according to the rules of large-scale photography
The simplest way to make casts from volumetric handprints is to use an aqueous solution of gypsum for this purpose. The disadvantage of plaster copies is the inaccurate reproduction of the features of the pattern of papillary lines, which makes it difficult to further identify the person who left them. In addition, there is a high risk of damage or even destruction of the resulting plaster copy of the traces under mechanical loads. This disadvantage can be avoided by using synthetic pastes “K”, “U-1”, “SKTN”, etc.
Superficial marks are formed mainly due to the layering of sweat or other substances covering the skin of the hands on the area of objects that a person has touched. Surface marks can be visible, barely visible or invisible. Visible surface marks occur when hands are stained with some foreign substance: paint, blood, etc. Low-visibility and invisible handprints are mainly sweat and fat prints.
Superficial peeling marks are much less common in practice. Such marks form, for example, on the freshly painted, dusty surface of objects. They are photographed and can only be removed together with the trace carrier.
The main difficulties arise when searching for low-visibility and invisible sweat-fat fingerprints. The search begins with identifying the most likely locations of traces. Analyzing the situation at the scene of the incident and, based on this analysis, mentally reconstructing the event that took place, the investigator makes assumptions about what objects the criminal could or should have touched with his hands. If these items have a smooth, well-finished surface (metal door handles, polished surface desk, window glass, etc.), then handprints are easily detected in oblique light. Transmitted light can also be used to detect sweat marks on transparent objects. Low-visible sweat and fat prints discovered in this way are subsequently processed with various powders to enhance contrast.
Invisible marks appear mainly on surfaces that absorb sweat and grease, in particular on paper, wood, wallpaper on indoor walls, etc. They can only be detected using special technical means, recommended by criminology.
In the process of searching for handprints, special care must be taken so as not to destroy the traces existing at the scene and not leave your own. Traces left by participants in an investigative action can mislead the investigator as to their origin, and subsequently the expert who will be entrusted with conducting a fingerprint examination.
To identify low-visibility and invisible fingerprints, forensic science has developed several methods and means: physical (various powders), chemical and physico-chemical. The first ones are based on the property of adhesion, i.e. the ability of powder particles to stick to sweat and fat secretions as a result of pollination of traces by them. Due to its accessibility and ease of use physical methods detection of hand traces has become widespread in practice. Fingerprint powders are made from magnetic and non-magnetic materials and are of great variety. They are selected depending on the characteristics of the trace carrier material, the expected age of leaving traces, the level of humidity of the surface of the trace-receiving object, etc. Specialists usually use mixtures of powders, which they prepare themselves by mixing known powders in certain proportions. Best qualities possess those powders and their mixtures that, when applied to a trace-receiving surface, adhere well to the sweat-fat substance of the trace and do not remain on clean areas of the surface being treated.
Non-magnetic powders are applied to the surface where traces are expected to be found by spraying, using a flute brush or in bulk. For spraying, special aerosol sprayers filled with powder are used. With their help, you can quickly process a large surface area.
After applying the powder and treating the surface of the object on which a sweat-grease mark is found, the powder must be carefully removed without damaging the mark. This can be done by simply shaking or blowing off any remaining powder. The remaining particles are removed with a fingerprint brush. When identifying fingerprints using highly soilable powders, such as nozzle soot or graphite powder, it is not recommended to use a fingerprint brush, since the brush, while removing excess powder, leaves small traces on the surface of the object, making further examination of such traces difficult.
Sweat marks are detected somewhat differently using magnetic powders, among which the most common is iron powder reduced in hydrogen. The powder is applied to the surface where a hand mark is found or may be found, using a so-called magnetic brush, which is a movable rod with a permanent magnet attached to the end. Iron particles are attracted by a magnetic brush, forming a kind of “brush” of powder particles. With gentle movements it is passed over the surface to be treated, while the particles of iron powder, adhering to the sweat and fat secretions, reproduce the papillary pattern. The use of a magnetic brush to identify fingerprints is most often not associated with the need to remove excess powder from the surface on which traces are found,
since this excess remains on the brush itself. Iron powder reduced in hydrogen is versatile and can be used to identify fingerprints older (up to two months).
When working with hand marks, powders are selected in such a way as to provide sufficient color contrast with the surrounding background. It is better to detect traces on multi-colored surfaces using powders that fluoresce under the influence of ultraviolet rays. This will greatly facilitate their visual perception and photographing before the developed prints are removed.
Fingerprints revealed using powders are photographed according to the rules of large-scale photography and then copied onto trace-copying materials. As such, special fingerprint films are mainly used: black, white or transparent, selected depending on the color of the powder that reveals the handprint. Dactyl films are made in two layers. One layer has a sticky surface, with which the film is applied to the mark and pressed tightly. After removing the film from the surface, an identified trace remains on it. The second layer of fingerprint film is designed to protect traces from possible damage. Made from transparent celluloid, it is applied to a sticky layer of film, covering the trace that has been developed and copied on it.
If handprints are found on uneven surface, then it is recommended to use synthetic pastes as trace-copying materials, to which a filler is first added (most often powders used to identify handprints), which provides a contrasting display of the copied trace.
From chemicals The method of identifying sweat marks on hands by fumigating them with iodine vapor has become widespread in practice. For this purpose, iodine tubes are used, which are a glass tube in which crystalline iodine is placed. The tube is closed at both ends with glass wool and one of them is connected to a rubber bulb. The iodine tube is heated by the heat of the hand (artificial heating is also used) and air is pumped through it using a rubber bulb. A stream of air along with iodine vapor is directed to the surface of the object, where hand marks may be located. The advantage of this method of identifying fingerprints is the ability to quickly process a large surface area. Particularly good results can be obtained when working with marks left on paper.
When using an iodine tube, it is necessary to remember that the traces detected with its help disappear after a short period of time as a result of the evaporation of iodine, which stains the sweat-fat print. This does not exclude the possibility of repeated fumigation of this trace with iodine vapor. However, it is better to immediately fix the traces identified with its help. To do this, photographs are taken and then the mark itself is fixed by treating it with a solution containing starch or a solution of orthotolidine. Copying sweat and fat prints treated with iodine vapor is only possible using special iodine copying films. If they are unavailable, you can use synthetic or adhesive pastes with the addition of orthotolidine or starch. You can also fix and then copy a trace developed with iodine vapor by treating the trace with iron powder reduced in hydrogen.
Chemicals in the form of special reagents are used to identify fingerprints of considerable antiquity. Considering the known complexity of working with chemical reagents, identifying handprints using this method should be carried out in laboratory conditions, having previously removed the traces along with the trace carrier. Silver nitrate, ninhydrin and a number of other drugs are used as developing reagents.
Physico-chemical agents are not widely used in domestic practice, although they have some advantages over other methods of identifying sweat-fat fingerprints. The reason here is not only the high cost of the equipment, but also the complexity of its use, which requires professional knowledge and skills. Physico-chemical methods are based on the property of some components of sweat secretions (fats and oils) to luminesce under the influence of ultraviolet rays or a laser, as well as the ability of the sweat substance in the presence of radioactive isotopes to become a source of radioactive radiation, which is detected using special devices. Fingerprints from significant dates can be visualized using, for example, radioactive bromine. The method is called the "bromination method". The prints developed with its help are distinguished by great clarity and high contrast of the image of the papillary pattern.
The discovered and seized handprints are described in detail in the investigative report. The record must contain information about the place where traces were found and the characteristics of the trace-receiving object (its color, material from which it is made, surface moisture, etc.). In addition, the protocol indicates by what technical methods and means the traces were discovered (visually during inspection of a specific object, in oblique light, using a powder of a specific name and color, etc.).
The description of the traces themselves should reflect their shape, size, general signs papillary pattern and, if possible, other features that allow one to individualize the detected fingerprint to one degree or another. Further, the protocol indicates the method of securing and removing the traces: seized together with the trace carrier, photographed according to the rules of focal and large-scale photography, marked on a scale plan of the scene of the incident, copied on fingerprint film of a certain color, etc. The description of handprints ends with an indication of the methods and means of ensuring their safety (packaging and labeling) and the fact that the participants in the investigative action verified the correctness of the record relating to the traces is noted. A record with the relevant details is also made on a tag that is attached to each seized trace.
Handprints seized from the scene of an incident or from the site of another investigative action are added to the materials of the criminal case in accordance with the requirements of the criminal procedure law. When packing items with traces, all precautions must be taken to prevent damage or destruction of traces during transportation and further storage. Proper handling of handprints at the point of detection, reliable packaging and safe storage will provide maximum opportunities for conducting fingerprint examination.
- For details on the possibilities of using various powders, see: Kornienko N.A. Human traces in forensics. - St. Petersburg, 2001. P. 72-79
- See, for example: Paul K.-D. Natural scientific criminology. M., 1985
- See: Vaganov P.A., Luknitsky V.A. Neutrons and forensics. - L., 1981. P. 84-85
Handprints are detected in several ways. Volumetric traces are detected using oblique illumination due to the shadow contrast of the recesses formed by the papillary lines. Surface colored marks are easy to detect in diffused light. If the color of the dye matches the background color, you need to select an appropriate filter or use a source of ultraviolet rays or use an electron-optical converter in the infrared zone of the spectrum.
The greatest difficulty is detecting traces of sweat and fat. The choice of one or another method for identifying them depends on the nature of the trace-receiving surface and how long ago the trace was left. Traces on smooth, reflective surfaces are detected visually. The effectiveness of this method depends on the optimal combination of lighting and observation. Relatively fresh marks on both smooth and rough surfaces can be identified by powder staining.
Depending on the color and adhesive properties of the trace-receiving surface, powders of different color, structure and specific gravity are used. Some sets of scientific and technical tools include universal powders “Sapphire” and “Ruby”, which give satisfactory results when processing marks on surfaces of varying degrees of roughness. "Sapphire" is a light universal mixture and is recommended for identifying marks on dark surfaces. To identify traces on light surfaces, use the dark universal mixture "Ruby". Single-component powders are also used to pollinate traces of sweat. Yes, zinc oxide powder white, gives good results when identifying marks on plastics, varnished surfaces, rubber, dermantine, and glass. Copper oxide, black powder, is used to identify marks on paper and painted surfaces. oil paint. Aluminum powder shows marks well on glass and other highly glossy surfaces. Graphite is used to reveal marks on paper. Lead oxide, orange powder, is used to detect traces on rubber, cardboard, and plywood. Reduced iron, a gray-brown powder, allows you to identify traces on any surfaces that do not have magnetic properties.
The pollination technique depends on the properties of the powder and the trace-receiving surface. The simplest method is to sprinkle powder on the surface to be treated and then shake off any excess. This is how sheets of paper are processed. A fingerprint brush is used when processing hard smooth surfaces. Rubber bulbs, medical powder blowers and other sprayers are used to apply powder to hard, rough surfaces. The so-called magnetic brush (a magnetized metal rod enclosed in a plastic housing) is used to treat surfaces with reduced iron powder. Fingerprints revealed by powders are removed by copying them onto fingerprint film. Surface treatment with powders and subsequent copying of traces onto fingerprint film is carried out only in cases where the trace cannot be detected visually or it is impossible to remove a visually detected trace with an object or part of it.
Staining traces with iodine vapor is a physical method. With the help of iodine vapor, traces appear on paper, wood, plywood, lime-whitened or oil-painted surfaces.
There are several ways to fix iodine stained marks:
- 1) Traces revealed by iodine vapor are photographed according to the rules of detailed photography;
- 2) Traces stained with iodine vapor are additionally pollinated with reduced iron powder. (In this case, iron iodide is formed, the trace acquires a persistent dark brown color and is firmly held on the trace-receiving surface);
- 3) A piece of photographic material moistened with distilled water is pressed tightly onto the iodine-fumigated trace. Then the photographic film or photographic paper is developed in the light, fixed, washed and dried. The image is obtained due to the fact that iodine at the points of contact with the photo emulsion layer acts as an attenuator.
Chemical methods for detecting invisible traces of sweat fat are based on the ability of some components of the sweat fat substance to enter into color reaction with chemicals such as silver nitrate, ninhydrin and alloxan. Silver nitrate is used in the form of a one percent solution in distilled water. After applying the solution with a cotton swab, the object is exposed to a bright sunlight or placed under a mercury-quartz lamp without a filter. Under the influence of ultraviolet rays, the silver chloride formed as a result of the reaction between silver nitrate and the chloride salts of the fatty substance turns into metallic silver, which colors the trace black. Ninhydrin and alloxan enter into a color reaction with protein breakdown products that are part of the fatty substance. They are used in the form of a one percent solution in acetone. When exposed to heat, ninhydrin turns the trace purple, alloxan orange. Identified chemical methods traces are recorded by photography. For the purpose of identification, seized traces and comparative samples - fingerprints of papillary patterns of the persons being examined - are sent for fingerprint examination. Depending on which areas of the skin surface left the traces to be examined, palm prints or prints of all ten fingers are made on blank sheets of paper using printing ink. Under each fingerprint, a record is made of which hand and finger it was made by. The sheets indicate who left the comparative prints and the signature of the person being checked. If the person being checked was previously registered with fingerprints, then his fingerprint card can be presented for comparison. As comparative samples, sweat-grease, stained or voluminous finger marks, the affiliation of which is known to a certain person, can be used.
The need to use such samples arises when it is impossible to obtain special comparative samples or when there is no fingerprint card of the person being tested. The safety of traces sent for examination is ensured by proper packaging. Handprints taken directly from a trace-receiving object are packaged so that the traces do not come into contact with the walls of the package. It is strictly forbidden to wrap unprotected items in soft packaging material. Eisman A.A., Expert opinion. Structure and scientific basis. M., 1967
The information provided about handprints, their identification and research show that work with them begins at the very initial stages detection and investigation of crimes. At the same time, great importance is attached to the knowledge and skills that both the investigator and the interrogator, who are the first to “come into contact” with traces of a person, must have. The effectiveness of the investigation and proof of guilt in the future depends on their ability to identify, preserve and correctly remove traces.
- 1. Before detecting traces of hands, it is necessary to take measures so that during the search not to destroy other traces present on the objects or to complicate their further research (shoe marks on the floor, microfibers on the window frame, traces of biological origin, etc.).
- 2. Objects with traces should be taken in such a way as not to leave your traces and not to destroy the traces of the criminal.
- 3. When identifying traces, it is first necessary to use visual detection methods, and then physical and chemical ones.
- 4. Avoid exposing objects with hand marks to sudden temperature changes.
- 5. First of all, traces are detected on objects that may be exposed to precipitation, thermal effects, mechanical damage, etc.
Ways to detect handprints:
1. Optical (visual) - for volumetric, colored or low-visibility traces. This method is based on enhancing contrast by creating favorable lighting and observation conditions.
These include:
- - illumination of a surface from a certain angle or inspection of a given surface from different angles;
- - viewing transparent objects against light;
- - inspection of the surface using a laser, UV ray sources, and using light filters.
This method is simple, publicly available and is used when using other methods for identifying handprints.
2. Physical methods are based on the adhesive (sticking) or adsorption (implementation) properties of a trace-forming substance, a trace-receiving surface, or a material used to identify.
These include:
a) the method using fingerprint powders is the most common in expert practice.
Requirements for powders:
- - size from 70 to 100 microns;
- - the powder should not form lumps and have no foreign inclusions;
- - when independently preparing dactyl powder from decomposition. components, they must be thoroughly mixed.
Powders are applied using a brush, powder blowers, or rolling over a trace-receiving surface.
b) using iodine vapor with fixation with reduced iron powder.
Detection of hand marks on the skin of a corpse: from a distance of 20-50 mm, the skin of the corpse at the place where the traces are supposed to be located is treated with iodine vapor and applied to the darkened area for 1-2 seconds. silver plate about 0.25 mm thick and 51 square meters in area. mm. After this, the trace is exposed to light. There are positive examples of this method, but it has not been fully explored.
- c) the thermal vacuum spraying method is based on the spraying of heavy metals (tungsten, molybdenum) in a vacuum. This colors the background. In practice, there are cases of identifying traces in this way even on a sheet of slate.
- d) a method based on the use of radioactive isotopes involves treating the surfaces of objects with radioactive materials.
- e) by sooting a flame - used to identify hand marks on polished metal surfaces. Its essence is as follows: when burning dep. objects (for example, casts made using paste “K”, polystyrene foam) will release a lot of soot, which is a fine powder, which is used to identify handprints.
- f) using liquid dyes, such as ink solutions.
In this case, the object with the trace is dipped into a bath of solution and then placed in running water.
- 3. Chemical methods - based on the chemical interaction of specially prepared solutions with elements of the sweat-fat substance. These methods are used to detect handprints on paper, cardboard, wood of various ages (in some cases up to several years) and are most often used in laboratory conditions.
- a) identifying hand prints using a solution of silver nitrate in distilled water:
A 0.5-10% solution of silver nitrate in distilled water (“lapis”) is prepared and the object with traces is treated using a cotton swab or spray bottle. After this, it is dried in the dark, otherwise the background will be heavily colored and appear under the influence of sunlight or with the help of UV illuminators. During development, visual control is required. Best results according to the Volgograd Higher School of the Ministry of Internal Affairs were obtained with the following solution:
- - distilled water - 100 ml.
- - silver nitrate - 1 gram.
- -citric acid - 0.2 grams
- -tartaric acid - 0.1 grams
- -nitric acid - 3-5 drops.
If traces of great antiquity are detected, the concentration of the solution is doubled.
b) detection of handprints using a solution of ninhydrin or alloxan in acetone:
A 1% solution is used, applied in a similar way, dried under a hairdryer or hot stove. In this case, traces treated with ninhydrin are colored blue-violet, and traces treated with alloxan are orange. Alloxan is cheaper, and traces treated with it have a bright crimson glow in UV rays. Traces appear from 2 hours to 1-2 days. Therefore, for operational purposes, the express method is used:
The prepared solution is applied in a similar way and after the acetone has evaporated, the surface is generously moistened with a 1% solution of copper nitrate in acetone, and then immediately subjected to intensive heat treatment. To do this, cover the object under study with a sheet of paper and run a hot iron over it (put it in a glosser and hold it over an electric stove). The marks appear immediately, are quite strong and there is no coloration of the background. The disadvantage is the dotted image of papillary lines in the patterns.
After ninhydrin, treatment with silver nitrate is possible.
d) identification of blood traces of hands - for this, a solution of benzidine in sleep and hydrogen peroxide is used (5 parts of a 1% solution of benzidine in alcohol and 1 part of three percent hydrogen peroxide. Blood traces treated with this solution are painted blue-green. The color is stable and additional does not require fastening.
fingerprint fingerprint hand
