LATENT PRINT DEVELOPMENT
Fluorescence Examination - Background
As early as 1933, fluorescence examination with UV light was suggested as a method of visualizing latent prints dusted with anthracene powder on multicolored surfaces. In 1976, researchers at the Xerox Research Centre of Canada discovered inherent latent print fluorescence via continuous wave argon ion laser illumination. Shortly thereafter, the first latent print in a criminal case was identified, using inherent luminescence via laser excitation (fingerprint on black electrical tape).
Blood Enhancement Techniques
Blood is one of the most common known contaminants of fingerprints found at scenes of crime. Use of the protein dye, amido black (acid black 1), quickly became popular with forensic investigators.
Chemically Treated Papers
Chemically treated paper is a class that encompasses thermal paper and carbonless specialty papers. These papers cannot be treated with the conventional amino acid reagent formulations described previously because the polar solvents react unfavorably with the chemical treatments applied to the paper during manufacture. This undesired interaction frequently causes the surface of the paper to blacken, obliterating the documentary evidence the paper contained
Deposition Factors
Deposition factors that influence the quality, or even the presence, of latent prints include the conditions surrounding the contact between friction skin and those objects that are touched.
Fluorescent Powders, Dye Stains, and Reagents
Dye Stains MBD [7-(p-methoxybenzylamino)-4- nitrobenz-2-oxa-1,3-diazole], rhodamine 6G (R6G), Ardrox, basic yellow, and basic red can be prepared in the lab and are extremely effective for enhancing fingerprints developed with cyanoacrylate. RAM, a combination of R6G, Ardrox, and MBD. Because RAM can be used at various wavelengths, the practitioner can often "tune out" problematic backgrounds by selecting a wavelength that maximizes fingerprint fluorescence and suppresses background fluorescence. Treatments for paper are equally effective as those used on nonporous surfaces and include ninhydrin toned with zinc chloride and the ninhydrin analogues: DFO, 1,2-indanedione, and 5-MTN (5-ethylthioninhydrin).
Post-transfer conditions
Environmental factors, are forces that affect the quality of latent prints after deposition Examples of these factors are physical contact from another surface, water, humidity, and temperature.
TYPES OF PRINTS
A patent print is simply a visible print. Patent prints can also be left in blood, paint, ink, mud, or dust. Latent prints are undetectable until brought out with a physical or chemical process designed to enhance latent print residue. A plastic print is created when the substrate is pliable enough at the time of contact to record the three-dimensional aspects of the friction skin. Clay, putty, soft wax, melted plastic, heavy grease, and tacky paint are all substrates conducive to forming and retaining plastic impressions.
Dermis
The dermis is composed of a variety of different connective tissues, including collagen, elastin fibers, and an interfibrillar gel composed of glycosamin-proteoglycans, salts, and water. This layer also contains the two major sudoriferous and sebaceous glands.
Tests for Protein and Its Breakdown Products
There are two types of techniques for proteins—those that stain proteinaceous material and those that react with amines. Blood contains more protein than any other material, so these techniques are inherently more sensitive than those for heme, although they are not at all specific for blood. The most effective protein dyes for the enhancement of fingerprints in blood are a group known as acid dyes.
Production of sweat
Three primary glands contribute to the production of sweat. These are the sudoriferous glands (eccrine and apocrine) and the sebaceous glands. Each gland contributes a unique mixture of chemical compounds. These compounds either exude from pores onto the friction ridges or are transferred to the friction ridges through touching an area (e.g., the forehead, underarm, etc.). The eccrine gland is one of two types of sudoriferous (or "sweat") glands present in the body. These glands produce a secretion that is mostly water but contains many compounds in trace quantities. The eccrine gland also secretes organic compounds. Of primary importance to the development of latent print ridge detail are the amino acids. Serine is the most abundant amino acid. Proteins are also found in eccrine sweat
Tests for Heme
Two kinds of tests use the heme group in hemoglobin: crystal tests and catalytic tests. Crystal tests are specific or confirmatory for the presence of heme, but not whether the blood is human or not. The two best-known crystal tests are those formulated by Teichmann and Takayama. The catalytic tests are only presumptive or infer the presence of heme because they are subject to false-positive and false-negative reactions caused by a variety of nonblood substances. The major concern with the catalytic tests for blood is that they can produce false-positive results in the presence of chemical oxidants and catalysts; salts of heavy metals such as copper, nickel, and iron; and plant peroxidases such as those found in horseradish, citrus fruits, and numerous root vegetables
Gun Blueing Reagents
Gun blueing of metals involves the simultaneous deposition of two metals, selenium and copper, on a metal surface. The bimetal deposited is blue-black in color.
Magnetic powder
magnetic or magna powder, allows 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.
Powders
Most commercial powders rely on at least two essential elements to provide adhesion to latent print residue without "painting" the substrate. These elements are referred to as pigment and binder. The pigment in fingerprint powder provides for effective visualization, offering contrast and definition against the background surface. The binder provides for maximum and preferential adhesion to latent print residue
Packaging
Packaging helps ensure the integrity of the evidence by keeping contaminants away, keeping trace evidence intact, and helping to guarantee chain of custody.
Anatomy of skin
Skin serves several functions, including regulation of body temperature, moisture retention, protection from invasive organisms (e.g., viruses, bacteria), and sensation. It is composed of two primary and distinct layers, the epidermis and dermis.
Textured Surfaces
Textured substrates can be porous or nonporous and present the problem of incomplete contact between the friction ridge skin and the surface being touched.
Indanedione
1,2-indanedione were first considered after a related compound, 6-methylthio- 1,2-indanedione, was found to produce fluorescent fingerprints. 1,2-Indanedione is a close analogue of ninhydrin and is theorized to react with amino acids in a very similar fashion. 1,2-Indanedione develops more fingerprints than DFO, ninhydrin, or the DFO-ninhydrin sequence combined. The indanedione-DFO sequence is capable of visualizing even more latent fingerprints than 1,2-indanedione alone, and indanedione can also enhance ninhydrin-developed fingerprints. Fluorescence can be observed under 520 nm illumination and viewed through a 590 nm filter
Fluorescence Examination
Fluorescence examination of latent prints is extremely sensitive. By using the correct barrier filters that will block out the light from the forensic light source being used, but not the fluorescence, a very high signal-to-noise ratio may be observed. Fingerprint examinations may produce fluorescence from four sources: • Native constituents in latent print residue • Foreign substances picked up by the hand and transferred through deposition • Intentional chemical enhancement • Substrate (background) fluorescence
Cyanoacrylate Fuming 1982
In 1982, latent print examiners from the U.S. Army criminal Investigation Laboratory in Japan and the Bureau of Alcohol, Tobacco, and Firearms introduced this technique to North America. Once CA fuming proved practical, with the introduction of methods to make the technique faster and more effective, it quickly gained acceptance worldwide.
Filters
In general, yellow filters are used for incident light wavelengths from UV to 445 nm, orange filters for light sources of 445-515 nm, and red filters for 515-550 nm.
Latent Print powders
Latent print visualization with powder, or "dusting", involves the application of finely divided particles that physically adhere to the aqueous and oily components in latent print residue on nonporous surfaces. This technique is one of the oldest and most common methods of latent print detection, with one of the earliest references dating back to 1891
Silver Nitrate Reagents - limitations
Limitation. The major drawback of the silver nitrate method is that the chloride ions in the latent print residue diffuse over time, and humidity accelerates this diffusion. This will affect the resolution (ridge detail) of the developed print. Normally, prints no older than 1 week will develop well; however, one should attempt to examine the evidence as soon as possible to avoid this diffusion.
Ninhydrin
Ninhydrin was first described in 1910 when Siegfried Ruhemann mistakenly prepared the compound. (2,2-dihydroxy-1,3-indanedione) also known as Ruhemann's purple, reacts to the detection of trace amounts of amino acids and protein products in biological samples. Ninhydrin is one of many chemicals that acts as a nonspecific amino acid reagent and is, therefore, highly suitable for fingerprint development. Ninhydrin is used on porous surfaces. Following treatment with ninhydrin solution, development should ideally proceed at room temperature, in a dark and humid environment (50-80% humidity), for a period of 1-2 days
Nonporous Surfaces
Nonporous surfaces do not absorb. These surfaces repel moisture and often appear polished. They include glass, metal, plastics, lacquered or painted wood, and rubber.
Cyanoacrylate Fuming enhancement
Once prints have been developed, they can be enhanced optically with oblique, axial, reflected, and transmitted lighting techniques; chemically enhanced with fluorescent dye stains; and physically enhanced with the application of fingerprint powder, in that order. Fluorescent dye staining and examination with a laser or forensic light source usually produces the most dramatic results. At this stage, proper photography can go beyond simply documenting the image to enhance the visibility of the fluorescing print by recording detail imperceptible to the unaided eye. Powdering is also a good way to visualize and document polymerized impressions.
Silver Nitrate Reagents
One of the first reagents used for developing latent prints on porous surfaces was a 1-3% aqueous solution of silver nitrate, AgNO3. The silver ions in silver nitrate react with the chloride ions in salt (sodium chloride, NaCl) contained in the latent print residue to form silver chloride (AgCl), a highly insoluble salt (Ksp = 1.8x10-10).
Porous Surfaces
Porous substrates are generally absorbent and include materials like paper, cardboard, wood, and other forms of cellulose.
Powder Brushes
Powders are typically applied to nonporous surfaces with a soft brush. Conventional brushes are typically made with animal hair, fiberglass filaments, or sometimes feathers.
PRE-TRANSFER
Pre-transfer conditions include the condition or health of the donor's friction skin and the amount and type of residue on the skin. These conditions are affected by age, gender, stimuli, occupation, disease, and any substances the subject may have touched prior to deposition.
Semiporous Surfaces
Semiporous surfaces are characterized by their nature to both resist and absorb fingerprint residue. These surfaces include glossy cardboard, glossy magazine covers, some finished wood, and some cellophane. Semiporous surfaces should be treated with processes intended for both nonporous and porous surfaces.
Aqueous Techniques
Silver nitrate reagents, silver physical developers, multimetal deposition processes, and gun blueing reagents.
Sudan Black B
Sudan black is a dye stain used for the detection of sebaceous components of friction ridge skin residue on nonporous and some semiporous substrates (e.g., latex gloves and some ceramics). This dye stain also detects friction ridge skin detail where the friction ridge skin or the substrate has been contaminated with grease, food residue, or dried deposits of soda or sweetened (e.g., by fructose or sucrose) drinks. It has also been used to enhance friction ridge detail previously treated by the CA fuming technique. Dried sudan black-processed prints have been lifted using conventional lifting tape (as used with the powder processing technique). It has been successful on waxy coated, glossy, and smooth substrates. However, it has been less successful on heavily contaminated, uneven, and semiporous substrates.
Epidermis
The epidermis is composed of several distinct layers The layer. situated just above the dermis is the stratum germinativum (basal cell layer), and the top layer is the stratum corneum (cornified layer). In this stratum, eleiden is converted to keratin, which is continually sloughed off the surface of the epidermis, resulting in a constant need to replenish the keratin that is lost. A cell beginning in the stratum germinativum typically travels through to the stratum corneum in about 28 days.
Process selection cont.
The following factors may influence the choice of development techniques as well as the level of resources used in any situation: • Type of latent print residue suspected • Type of substrate • Texture of substrate • Condition of substrate (clean, dirty, tacky, sticky, greasy, etc.) • Environmental conditions during and following latent print deposition • Length of time since evidence was touched • Consequences of destructive processing methods • Subsequent forensic examinations • Sequential ordering of reagents • Seriousness of the crime
Process selection
The following general procedures are appropriate during a systematic search for latent fingerprint evidence: • Visual inspection with a bright light, forensic light source, or laser • Sequential latent print processing • Documentation of developed prints at each step
Latent Print residue
The latent print secretion is a complex emulsification of these numerous and varying compounds. When deposited on a surface, nearly 99% of the print is composed of water. Latent print residue is generally divided into two basic categories, water-soluble and water-insoluble.
1,8-Diazafluoren-9-one (DFO)
The reagent is widely used in sequence with ninhydrin to develop fingerprints on porous surfaces. Unlike the ninhydrin reaction, the DFO reaction requires a high-temperature, low-humidity environment. The combination of DFO followed by ninhydrin develops more latent fingerprints than DFO or ninhydrin alone. DFO solution can be applied to specimens by dipping, spraying, or brushing, although dipping is the preferred method. The exhibit is allowed to dry and then heated to promote development. Several heating methods are suitable: heating in a 100 °C oven for 10-20 minutes. Mechanistic studies of DFO's reaction with amino acids have shown that the presence of methanol is essential. This allows the DFO to form a hemiketal which is less stable than the parent structure and therefore more reactive, producing a more sensitive response to amino acid residues in fingerprints
Silver Physical Developers
The silver physical developer originated in photographic chemistry as an alternate method to the chemical developer for developing film. A silver physical developer is an aqueous solution containing silver ions and a reducing agent that reduces the silver ions to silver, but it also contains two other sets of chemicals: The silver physical developer currently used for latent print development on porous surfaces contains silver ions (silver nitrate) and ferrous ions (ferrous ammonium sulfate) as the principal components; citric acid and ferric ions (ferric nitrate) as the set of chemicals that suppress the formation of spontaneously formed colloidal silver particles; and a cationic and non-ionic surfactant as the set of chemicals that suppress the growth of such particles. The procedure for using the silver physical developer involves three treatments in sequence and in the same glass tray.
fluorescence in blood
The use of fluorescence to enhance fingerprints in blood can be extremely effective. There are two ways this may be achieved: (1) by exciting fluorescence in the background surface on which the blood is deposited or (2) by treatment with a chemical that either breaks the heme group or turns the blood into a fluorescent species, or does both of these.
Water Insoluble
The water-insoluble portion can really be divided into two subcategories. One fraction of this residue is composed of large, water-insoluble molecules (e.g., proteins) and the other fraction is composed mainly of nonpolar lipids (e.g., fatty acids).
Water soluble
The watersoluble portion of the print deposit is typically composed of eccrine secretions like salts (e.g., NaCl) and amino acids (e.g., serine, glycine). Chemicals like ninhydrin (which reacts with amino acids) and silver nitrate (which reacts with sodium chloride) are effective reagents for visualizing this water-soluble portion of the residue.
Recording of Powder prints
There are two ways to record or preserve a powdered impression. The most common and simplest method is lifting. To lift a print, good-quality transparent tape is placed onto the surface bearing a powdered impression. If the impression will be photographed in situ, the importance of powder color increases. Documenting powdered impressions this way requires combining proper selection of powder and photographic lighting that will produce ample contrast against the substrate.
Transfer conditions
These are the conditions of the surface (substrate) being touched, including texture, surface area, surface curvature or shape, surface temperature, condensation, contaminants, and surface residues. The pressure applied during contact (deposition pressure), including lateral force, also contributes to transfer conditions.
5-Methylthioninhydrin (5-MTN)
This analogue reacts with amino acids in a manner identical to ninhydrin because the reactive, chromogenic core of the molecule is not changed by the addition of the sulfur group. As a result, 5-MTN-developed fingerprints are a shade of purple similar to ninhydrin-developed fingerprints. Development of 5-MTN-treated fingerprints requires heat and humidity, much the same as ninhydrin development.
Evidence Handling
To prevent damage to fingerprints on these surfaces, evidence should be handled in areas not normally touched or on surfaces incapable of yielding viable fingerprints. It should also be noted that the use of gloves does not preclude the transfer of friction ridge detail from the examiner to the exhibit.
Fluorescence Examination
Today, evidence that would be barely perceptible or even invisible under normal lighting is routinely intensified by fluorescence. Bloodstains, semen, bruises, bone fragments, questioned documents, flammable residues, fibers, and fingerprints all merit examination with a forensic light source or laser.
Vacuum Metal Deposition
Vacuum metal deposition (VMD) is a long-established industrial technique for the application of metal coatings to components such as glass to form a mirror. The best results were obtained by the use of a combination of metals, typically gold or silver followed by cadmium or zinc. Gold was preferred over silver as the initial deposition metal because silver can be degraded by fingerprint secretions and atmospheric pollutants. The range of specimens that have been successfully treated using VMD is extensive and includes: • Plastic bags and packaging. • Glass and plastic bottles. • Firearms. • Glossy card, photographic paper, and magazine covers. • Clean leather items (including handbags and shoes). • Adhesive tapes (nonsticky side).
Cyanoacrylate Fuming
also called superglue method. Most liquid super glues are really either methylcyanoacrylate or ethylcyanoacrylate. Super glue reacts with the traces of amino acids, fatty acids, and proteins in the latent fingerprint and the moisture in the air to produce a visible, sticky white material that forms along the ridges of the fingerprint. The final result is an image of the entire latent fingerprint. This image can be photographed directly, or after further enhancement. However, the glue must be in gaseous state. To do this, one places the surface suspected of containing a latent fingerprint in a container with a heater in it. Then, they place a small, opened container of the glue on top of the heater, and carefully seal the overall one. After that, simply wait. Currently, the heat-accelerated technique in controlled high humidity (60-80% relative humidity) is most often the suggested method of application.
