Fingerprints are used to identify an unknown victim, witness, or suspect, to verify records, and most importantly, as links and matches between a suspect and a crime. Even when you have no suspect, prints can develop leads, and sometimes provide clues about the criminal’s size, sex, and occupation. Small prints tend to be made by small people, and prints on a wall indicate the suspect’s height.
Construction workers tend to have rough hands, and musicians tend to develop calluses on the tips of their fingers. It’s important not to rely too heavily on these clues as they are not facts. Prints can substantiate or disprove the story of a victim or witness by locating their prints where they said they where. Even the absence of prints may be a key factor. Suicide scenes, for example, should never show any attempt at wiping prints away.
Occasionally, a print is found that is made with the palm of the hand or a bare foot. These are ordinarily processed by the same methods used for fingerprints. Several months before a baby is born, ridges develop on the skin of its fingers and thumbs. These ridges arrange themselves in more or less regular patterns. For purposes of classification, experts divide these ridge patterns into three basic classes: ARCHES, LOOPS, AND WHORLS.
Each class can be further divided into numerous sub-categories. See this other site on the Internet, Fingerprints 101, for more information and images of arches, loops, and whorls. As far as arches, loops, and whorls go, there are some slight racial variations. People of African ancestry tend to have plenty of arches; people of European background have frequent loops; and Asians/Orientals have a fairly high frequency of whorls.
Fingerprints are made of ridges on the upper skin on hands and feet of all people and some animals.
History Of Fingerprinting. Also known as dactylography, is definitely not a new technique. About 1750 years BC, the people in Babylon used fingerprints to sign their identity on clay tablets. In about the year 220 the Chinese were the first to use ink prints, but then after that fingerprints became forgotten for several hundred years. In 1686 a man called Malpighius. Malpighius wrote describing the ridges on fingerprints, but stopped at that.
Then in 1823 J.E. Purkynie discovered it was possible to classify fingerprints, and from there the use of fingerprinting began. In 1858 Sir William Herschel demanded labourers to sign contracts with fingerprints in India, and later in 1877 he suggested taking the prints of prisoners. In 1880 Doctor Henry Fauldspublished a piece on the use of fingerprinting in England, and two years later Gilbert Thompson used thumbprints on cheques to avoid fraud in the USA.
Between the years 1901 and 1910 many countries began using fingerprints, and soon, in 1924 in America, the Identification Division from the FBI started. Methods Of Detecting & Taking Latent Prints Nowadays fingerprinting is used widely across the world, with many uses. One major use of fingerprinting is in criminal investigations. Something that is commonly carried out at crime scenes is fingerprinting, through different methods.
Fingerprints may be found and collected at crime scenes, and later used to link suspects to the scene of the crime. Fingerprints can sometimes be seen on their own, such as prints on glass. But often they are not visible to the eye, and so methods of making prints visible are used. There are several methods of detecting latent prints.
Powder And Tape — Probably the most well-known method of detecting latent prints is dusting for them. A variety of powders are used in dusting for prints, many containing aluminium or carbon. This finely crushed powder is gently applied to a surface, and the minute particles of powder cling to the print residue, making it visible to the human eye. These prints are then lifted using adhesive tape. For dusting to work, the surface that is being dusted must be completely dry and relatively free of other contamination.
Magna Brush — This is a magnetic wand that attracts iron. It is dipped in iron dust, and the particles cling to it. This is then used the same as dusting using carbon and aluminium powders. The Magna Brush is also less messy, as any excess iron particles can be easily collected with the Magna Brush. A variety of fluorescent colours are available for this, and some of these powders reflect alternative light sources such as UV and lasers.
The cyanoacrylate fuming method — The cyanoacrylate fuming method, also known as the superglue fuming method, has proved to be another very useful way of detecting latent prints. This method was first used by the Criminal Identification Division of the Japanese National Police Agency in 1978. Shortly after this it was adopted in the US, and now it is a commonly used method of detecting prints. Most superglues are methylcyanoacrylate or ethylcyanoacrylate. This reacts with the traces of amino acids, fatty acids, and proteins in fingerprints as well as the moisture in the air, making them visible.
Ninhydrin — Another common method of fingerprint detection is the use of ninhydrin. This is sprayed, swabbed or dripped onto the surface. Ninhydrin reacts with the amino acids in the prints, forming a purple or pink compound.
Iodine Fuming — Iodine crystals are placed in a glass tube known as a fumer. The examiner then blows into the fumer, causing the transformation from solid to gas. The iodine vapours are emitted from the other end, and if the tube is aimed at a latent print, it will become visible for a short time.
Silver Nitrate — Silver Nitrate is a less toxic way of detecting prints on paper. Silver chloride turns black in light, and one of the components of sweat is sodium chloride. The silver nitrate is placed with distilled water and applied to the paper. The paper is exposed to light, and any prints will turn black.
Amido Black — Amido Black is a chemical used to develop fingerprints in blood. A fixing agent is first applied to the blood stain, and then amido black is used. There are other methods of detecting latent prints, most similar to the techniques mentioned above. Some methods even include laser technology. Different surfaces will require different techniques for developing latent prints. For example, when developing a print on paper, Ninhydrin should be used, though powders may work but not as effectively.
When developing prints in blood, Amido Black should be used, and powder works best on non-porous surfaces. When taking fingerprints from people, ink is rolled over the fingers and then the fingers are pressed down on papers or cards. However when it comes to fingerprinting the dead, it does not come so easy. If we are fingerprinting a corpse recently deceased, there is no problem. However if we are dealing with decomposition or mummification where the skin has become hardened and contracted, a special method is required.
Usually the fingers are soaked in a solution of glycol, lactic acid and distilled water, softening the finger tissues. If the skin has been wrinkled by the damp, the fingers can be printed by either use of a hypodermic syringe, gently manipulating the fingertips by hand, or removing the finger skin altogether and mounting it to be printed. Fingerprints found at crime scenes are very rarely fully intact, which means the quality of the print is lower, and can be more difficult to positively match.
When multiple sets of prints are being compare, a certain number of characteristic points must be a match. Worldwide there is no set number of how many points must match before it is accepted as a match, but it does differ in some countries. For example, in the Netherlands 12 points are required, whereas in Africa only 7 points are required. It also differs within some countries too. Paris has a requirement of 17 points, whereas the rest of France only requires 12.
Other Uses Fingerprints are not just used to connect criminals to crime scenes though. When human remains are found, fingerprinting is a very common way of identifying them. Fingerprints are also used for security reasons, such as on certain ID cards and as entrance control at important buildings. No Prints In very rare cases some people are actually born without any prints on their fingers, palms or feet. Though this can be a condition people are born with, some people’s ridges degenerate during their lives.
Fingerprint Databases. Automated Fingerprint Identification System, or AFIS, is a database of fingerprints taken and stored in the United States, though other countries such as Canada and the United Kingdom also have their own AFIS. The prints may have been taken for a number of reasons, and the system is used for a variety of purposes, including criminal identification, receipt of benefits, background checks, and receipt of credentials.
The machine used to scan fingerprints is called the LiveScan Device. AFIS makes it possible to sift through vast amounts of fingerprints every second, and the computer marks all minutiae (individual characteristics) it recognises. The technician goes over these points the computer has marked, submits the minutiae to a one-to-many search, and the computer gives the results with a percentage of matched minutiae points. A latent print examiner then checks through the possible matches to determine the most likely match.
The FBI-NCIC classification system and other techniques based on the HENRY FRACTION assign numerical values to overall patterns on an entire set of ten prints. This allows the coding and filing of millions of prints in an orderly manner. Tens of millions of prints are on file. In addition, police departments usually keep a file of UNIDENTIFIED PRINTS from open or unsolved cases.
If matches are found at a later crime scene, it proves the same person was involved in both cases. Also, as suspects are arrested and booked, their prints are compared with those in the file. Prints are most commonly made or made in: PLASTIC, which are impressions left in soft material like wax, paint, or putty; VISIBLE, which are made by blood, dirt, ink, or grease; and LATENT, which are normally invisible and must be developed before they can be seen and photographed. Print evidence is fragile.
A touch will destroy one. It’s possible to develop prints from snow or mud, and small objects that contain trace evidence also usually contain prints. Automobiles are a frequent source of prints. The most common automobile locations are the door, trunk, hood handles, outside mirrors, license plates, trunk release, emergency brake release, seat adjustment levers, seat belt buckle, and rear view mirror. Prints are difficult to remove from rugs and furniture.
When fingerprint evidence is photographed, a complete record of all technical data about the camera, lens, film, shutter speed, lens opening, illumination, camera position, distance from object, and angle is also kept. This protects the police department from charges that it’s the photography which makes it look like a match. Also, in the interest of good public relations, household furnishings are usually protected with a drop cloth while police are dusting for prints. With photos, three different exposures are usually taken: a regular exposure, an underexposure, and an overexposure. The most popular developing technique is DUSTING.
The principle upon which dusting works is simple. Most people’s fingers carry a coating of perspiration and oil. When fingers come into contact with any relatively smooth surface, the friction releases the oil from between the ridges. It is for this reason, fingerprinting is sometimes called friction ridge pattern analysis. When powder is applied to the surface, it sticks to the oil and brings out the pattern. Dusting is ideal on wood, metal, glass, plastics, Formica, and tile. It is less than ideal on paper, cardboard, and leather. Powders vary in color, stickiness, photographic and magnetic qualities.
The most common colors are black, white, gray, aluminum, red, and gold. The best color to use is one in sharp contrast to the surface color. For example, a white or gray powder works best on a dark surface, and a black powder works best on a whiter surface. In multicolor situations (such as a magazine cover or cigarette pack), it’s best to use a FLUORESCENT powder. When the dusted object is exposed to ultraviolet light, the powder will glow, making the print show up regardless of the background color.
With porous materials (such as leather, rawer wood surfaces, paper and cardboard), the preferred technique is to use a MAGNETIC powder where finely ground iron particles are suspended onto the surface using a magnetic wand. When a large area needs to be powdered, a large brush is used, such as one made of ostrich feathers. Once a print is located, it is moved in on with a smaller brush that’s easier to manage. Before any brush is used, it is shaken until the bristles spread apart and become fluffy.
Powder is never poured directly from a jar. Instead, a little is poured on a piece of paper and used as a palette. The tip of the brush is dipped in the powder, and then tapped gently to remove excess powder. Brushing is done lightly, swinging it in short, fairly quick, uniform strokes. An expert will try to follow the general direction of the ridges. The next step is called lifting the print. Lifting involves using some adhesive material to remove the powdered print from the surface.
The three most common lifting materials are hinged lifters, rubber lifters, and cellophane tape. If tape is used, a high quality clear transparent tape is best, not some glossy or opaque magic tape. The tape is unrolled a little at a time and folded over a bit to use as a tab for handling. It is important that the handler not get their own fingerprints on the tape. The handler will pull on the roll of tape so that the rest of the exposed tape is kept slightly taut, and cover the print area about an inch beyond in the other direction.
They will be careful not to get air bubbles under the tape. Bubbles destroy the value of the print. The tape is gently rubbed over the print. After the tape is firmly in place, the print is lifted by pulling the roll gently and evenly away from the surface. Then, there will be a quick application of the tape to a card or piece of paper. Excess tape will then be cut away.