IMPRESSIONS, FINGERPRINTS AND TRACE EVIDENCE
"Regrets are as personal as fingerprints" (Margaret Culkin Banning)
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 tend to 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 the NIST image database for pictures, here, here, or any of the stock image photo galleries on the web). 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.
The process of analyzing fingerprints is known as dactylography, and the origins of this science are interesting. One day in 1858, a British magistrate named William Herschel who worked in a village in Bengal, India hit on the idea that each print was unique and unchanging. There had already been a tradition in India, and especially among Bengalis (who were held to be notoriously deceitful) to use one fingerprint as a signature, but Herschel had this one Bengali he was particularly suspicious of, so he had all his fingers and palms printed. This turned out to be valuable in a contract dispute that later occurred. By 1888, mostly due to the initiative of a Buenos Aires police officer names Juan Vucetich, the practice of taking prints of all fingers became fairly standard. Around 1890, Francis Galton (a cousin of Charles Darwin) did some mathematical calculations on fingerprints, and provided the scientific basis for their legal admissibility. In 1891, Edward Henry (a Bengali Police Inspector who later became assistant commissioner of the London Metropolitan police) resurrected Herschel's idea and expanded it into a system of classification. By 1900, Scotland Yard started to abandon the clumsy French (Bertillon) system it was using, which required, among other things, measurement of the length of the middle finger, and started to use what became known as the Galton-Henry system, which eventually became the FBI-NCIC system. The first criminal trial to result in a conviction based primarily on fingerprint evidence took place in 1901. Fingerprinting was not only used to identify criminals in most countries, but also to register aliens, Jews, and ethnic groups. Opposition to fingerprinting was a part of Gandhi's peace movement in India from 1906 to 1947 as well as a part of the Anti-Apartheid movement in South Africa from 1959-1994 because of the strong association of it with criminality.
In addition to ridge patterns, there are minute variations and irregularities in the ridges themselves. These are called RIDGE CHARACTERISTICS. Examples of ridge characteristics are RIDGE DOTS, BIFURCATIONS, SHORT RIDGES, RIDGE ENDS and CROSSINGS. Each print has its own unique combination of overall pattern and special ridge characteristics. No two prints have ever been found that were exactly alike. Even those of identical twins are different. Prints remain the same throughout life.
When prints are found, an expert compares them with samples known to have been made by a suspect. He/she first compares ridge patterns and then looks for ridge characteristics. When these match, they are known as POINTS OF COMPARISON. The general rule in America is that prints must match at least twelve (12) points of comparison before an identification can be regarded as positive. The prints you find at a crime scene aren't always complete. This doesn't keep them from being used for comparison. What counts is the number of points of comparison. A partial print from just one finger may be all that's necessary.
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.
At least three other methods, other than dusting, exist for developing latent prints. IODINE FUMING works well on porous surfaces such as paper and unfinished wood, especially if the prints are fresh and/or if the purpose is to find out if they're fresh. This technique also leaves no trace, so no one can tell that you've looked for prints. The procedure involves placing a few iodine crystals in a fuming pipe, heating the pipe with a lighter or match, and blowing the iodine fumes through the mouthpiece of the pipe onto the surface. Iodine fumes are purple in color, although the prints that develop will be yellowish brown. Prints developed by this method disappear rapidly, so they must be photographed quickly.
Another method is NINHYDRIN SPRAY. This is a particularly useful method for all kinds of surfaces, including books and wallpaper, and is designed to develop prints that may be very old. Ninhydrin will develop prints made over 30 years ago. Ninhydrin produces a blue-violet color on the developed print. The area is sprayed until it is damp but not saturated. It is important to make sure the area is well ventilated. Drying takes from ten to twenty minutes, but the process can be hastened by using a heat lamp.
Another method is SILVER NITRATE. This involves spraying silver nitrate onto a surface (such as wood or cardboard) with an aspirator, or it can be applied with a brush or swab. After the liquid is in place on the surface, it is left to dry for about five or ten minutes, then the area is exposed to ultraviolet light, but regular bright light works just as well sometimes. This method produces a clear, crisp print because the chemical picks up on the salts in the perspiration. Prints developed this way also disappear after a short time, so lifting and analysis is done via photography.
A fairly recent method is SUPERGLUE FUMING. Police departments will use a big storage container or aquarium along with a hotplate, like the kinds that keep coffee cups warm. A few drops of superglue is placed on the hotplate, and the the object containing prints is placed into the container. The hotplate is turned on, the container is sealed, and in about fifteen or twenty minutes, any prints that were invisible are now visible in grayish tone on the object.
The most recent method is LASER, which is in essence the use of photoluminescence techniques, similar to the use of IONS, and other charged particles, as the latest cutting-edge methodologies.
|Fingerprint evidence has always been the gold standard
of scientific evidence. Experts and even police officers have always been
able to state that a "match" exists whenever twelve or more points of
comparison are found. In January 2002, a federal judge called into
question that 100-year-old practice of using points of comparison, saying
that fingerprint evidence has not been subjected to strenuous reliability,
validation, and peer review. Judge Pollak's ruling permits experts to
only point out similarities and not matches. Currently, experts in this
area are attempting to document the rates of matches and mismatches, and
Judge Pollak seemingly reversed himself in March 2002. However, in
October 2007, Baltimore County Circuit Judge Susan Souder refused to
allow a fingerprint expert to testify that a latent print was made by
the defendant in a death penalty case. Judge Souder said that
fingerprint analysis is "subjective, untested, and unverifiable."
Not in question at all is the matter of whether each person's
fingerprints are unique and permanent. That's undisputed.
What is more at question is whether one can determine with adequate
reliability that the finger that left an imperfect impression at a crime
scene is the same finger that left an impression (with different
imperfections) in a file of fingerprints. A couple of good
articles on the subject of fingerprint reliability are:
(1) Epstein, R. (2002). "Fingerprints meet Daubert." 75 Southern California Law Review 605.
(2) Cole, S. (2002). Suspect Identities. Boston: Harvard Univ. Press.
All trace evidence winds up in a crime lab. Most of it gets compared with a database or standard control samples, while other trace evidence is subjected to extensive independent analysis. Trace evidence, so called because it's so small it can easily be missed, may consist of a variety of things. The main points in collecting trace evidence is to look for things that appear to be foreign to the crime scene and may have evidentiary value. What you DON'T want to even think about doing is calling in the bulldozers and sifting thru the rubble. That kind of overkill is reserved for mass disaster and/or terrorism crime scenes. Also, there's ultratrace, or microtrace, evidence, which consists of microscopic elements that can only be detected in an advanced lab, like how the Food & Drug Administration's labs search for contaminants in FDA-regulated substances.
HAIR -- Unusual amounts of hair at a crime scene usually indicates a struggle took place. Hair is typically found on the floor near the weapon or point of impact between suspect and victim. Hair with the root pulled out may provide individual DNA evidence. Otherwise, hair has class characteristics. There are fourteen different elements that can be identified in a hair sample, however, and even mitochondrial (non-nucleus) DNA can sometimes be obtained without a hair root as it can from fingernails, toenails, and skin flakes.
FIBER -- This kind of trace evidence (carpet or clothing fiber) is usually collected from clothing, carpeting, furniture, beds, and blankets. Cross-transfer of fiber often occurs in cases where there is person-to-person contact. There are over a thousand known fibers, and several thousand known dye formulas. Fortunately, every dye formula manufactured is registered in a database.
GLASS -- Small pieces of broken glass (from doors, windows, or decorations) are frequently found on clothing and footwear. It is also sometimes found on the weapon, tools, and skin. Different types of glass have different densities and known refractive indexes.
PAINT -- Small chips of paint (from doors, walls, or furniture) are often found on weapons, pry bars, blunt objects, clothing, and shoes. A somewhat serious struggle or force will chip paint. There are forty thousand different types of paint classified in a database available to police. Most paint evidence submitted to a lab will come from hit-and-run cases involving automobiles.
DUST/DIRT -- This kind of trace evidence reveals where a person has been, where they live, where they work, and whether they have pets. Alibi soil samples are frequently taken in many criminal investigations. Most soil samples are from the top surface of the soil, and involve taking little more than a tablespoon. POLLEN is a subtype of dust/dirt that reveals where a person has been outdoors.
FIREARMS -- This kind of evidence involves ammunition, components, and residue. It typically consists of a whole host of family characteristics. Bullets are never removed from their holes; instead, the whole surrounding surface is cut out. Also, bullets are usually never marked. Gunshot residue from the hand or face needs to be done within six hours, and a lab can compare it with target residue. The science of ballistics is sometimes used for crime reconstruction.
So far, we've been talking about trace evidence that has mostly class characteristics. We now turn to trace evidence (like fingerprints) with individual characteristics.
FLUIDS -- Semen, saliva, or sweat, in fresh, coagulated, or dried form is usually found on spatters, drops, or stains. Each form has its own particular method of collection and preservation. Most testing involves polymarking, which is essentially DNA testing. Bodily fluids, including vomit, are frequently found at scenes involving alcohol, drugs, and poisons. Cigarette butts may have evidentiary value if they contain dried saliva, but police are in the habit of collecting every butt anyway. Semen containing sperm is particularly valuable, although the P-30 protein can individualize even fertile and vasectomized males. Biological evidence must be transported to the lab quickly.
BLOOD -- Every body has about ten pints, and there are 150 known proteins, 250 known enzymes, and many more antigens. At the scene, investigators often estimate the time a crime occurred from how dry the blood is. The shape of blood at the scene (pool, drops, stains, or splashes) also provides clues as to what happened. Recording the location and description of bloodstains is usually the most detailed part of crime scene photography, sketching, and note-taking. A specialized technique known as bloodstain pattern analysis is one of the most common methods of reconstruction. Blood evidence is frequently used to eliminate a pool of suspects.
BITE MARKS -- Every one of the thirty-two teeth in humans are unique due to age and wear. Bites usually tell how quickly the offender subdued the victim. Bites can often be matched to dental records.
SHOEPRINTS -- Most people's shoeprints show individual signs of wear, and are fairly unique given gait, walk, and modus operandi. Footprints are better than shoeprints for this purpose, but shoe impressions, like tire impressions, often contain contaminates or traces of evidence on them. Shoeprints are technically impressions, not imprints, because they are left on a soft surface. Detectives often like to record shoeprint and tire impressions in their notebooks or sketches. Only after it is certain that all residual trace evidence is cleared from the impression area is a plaster cast mold taken.
TOOL MARKS -- When a tool is made and used, it acquires tiny nicks and chips that characterize its blade and edges as well as picks up traces of substances it came in contact with. Tool marks are most commonly found along with a known modus operandi at burglaries involving windowsills, window frames, doors, door frames, cash register drawers, file cabinets, and any locked piece of furniture.
WOUNDS -- These can often be matched to weapons, tool marks on the weapon, or at least the weapon's size, shape, and length. A specialized technique known as wound pattern analysis often provides behavioral clues.
QUESTIONED DOCUMENTS -- Each person's handwriting is unique as are most of the machines used to communicate with. Document examiners can establish similarities in handwriting, and computer forensics specialists can extract logs and "slack data" from most devices.
Collecting & Preserving Blood Evidence from a Crime Scene
FBI Manual for Collecting Trace Evidence
FDA's Forensic Center: Speedy, Sophisticated Sleuthing
Fight the Fingerprint
Footwear, The Missed Evidence
Forensic Palynology: A New Way to Catch Crooks
History of Fingerprints
International Association of Bloodstain Pattern Analysts
Legal Challenges to Fingerprints
Nolo Guide to Fingerprint Evidence
Abbott, J. & A. Germann. (1964). Footwear Evidence. Springfield: Charles Thomas.
Ashbourn, J. (2000). Biometrics. London: Springer-Verlag.
Beavan, C. (2001). Fingerprints: The Origins of Crime Detection. NY: Hyperion. [Sample Pages]
Champod, C. et.al. (2004). Fingerprints and Other Ridge Skin Impressions. Boca Raton, FL: CRC Press.
Cole, S. (2001). Suspect Identities: A History of Fingerprinting and Criminal Identification. Cambridge, MA: Harvard Univ. Press.
Coppock, C. (2001). Contrast: A Guide to Fingerprint Identification Concepts. Springfield: Charles C. Thomas.
Cowger, J. (1983). Friction Ridge Skin Characteristics. Boca Raton: CRC Press.
Lee, H. & Gaensslen, R. (2001). Advances in Fingerprint Technology. Boca Raton: CRC Press.
MacDonell, H. (1993). Bloodstain Patterns. Corning, NY: Laboratory of Forensic Science.
Menzel, R. (1999). Fingerprint Detection with Lasers. NY: Marcel Dekker.
Norris, D. & Bock, J. (2000). "Use of Fecal Material to Associate a Suspect with a Crime Scene." Journal of Forensic Science 45:178-181.
Ogle, R. & M. Fox. (1998). Atlas of Human Hair Microscopic Characteristics. Boca Raton: CRC Press.
Ragle, L. (1995). Crime Scene: From Fingerprints to Autopsies. NY: Avon Books.
Saferstein, R. (2001). Criminalistics. 7e. Upper Saddle River: Prentice Hall.
Saferstein, R. (1998-2001). Forensic Science Handbook, Vols. I-III. Upper Saddle River: Prentice Hall.
Last updated: Mar 15, 2012
Not an official webpage of APSU, copyright restrictions apply, see Megalinks in Criminal Justice
O'Connor, T. (2012). "DNA Fingerprinting," MegaLinks in Criminal Justice. Retrieved from http://www.drtomoconnor.com/3210/3210lect03.htm.