The persistence and uniqueness of fingerprints make them a crucial component of any criminal investigation or background check. Prints do not change over time; their patterns form in utero and grow proportionally as the individual possessing them grows. The only way fingerprints can change is through permanent scarring caused by an external source. Despite there being nine basic fingerprint patterns, no two sets of prints are identical. They are unique to each person.
Fingerprint Use in History
Ancient Babylonians used fingerprints for recording business transactions, and Persian officials used them on government documents in the 14th century. While they served as a rudimentary form of identification in many cultures, it wasn't until the 19th century that they became a vital component of law enforcement investigations. The first recorded use of fingerprinting in a criminal investigation was in 1891 when Juan Vucetich, an Argentinian police official, made prints of a suspect in a homicide case. A year later, British anthropologist Sir Francis Galton published the first book on fingerprints in which he identified the individuality and uniqueness of fingerprint patterns. These small but specific characteristics of fingerprints officially became known as minutiae.
In 1901, an inspector general of police in Bengal, India, Sir Edward Henry, developed the first system of fingerprint classification. Law enforcement in the United Kingdom eventually adopted Henry's system, and its use quickly spread throughout the world. By 1903, most prisons made fingerprints the primary means of identification, and U.S. military and police agencies soon followed suit. In 1911, U.S. courts finally accepted fingerprinting as a valid means of identification.
Since 1924, the Federal Bureau of Investigation has been the national repository for fingerprints in the U.S. The system for matching prints was a slow process in the early days; examiners would match prints manually based on a card system. Doing this could take several days or weeks and made it challenging to solve serious crimes promptly. In the 1960s, the FBI began automating its fingerprinting system.
Today, the FBI processes fingerprints digitally through its Integrated Automated Fingerprint Identification System. Contributing agencies submit fingerprints electronically or through email for background checks or criminal investigations. The IAFIS responds within two hours for criminal fingerprint submissions and in less than 24 hours for civil fingerprint submissions. Currently, there are over 70 million fingerprint cards in the IAFIS database.
How Fingerprints Are Used
Fingerprints provide biometric security by controlling access to areas or systems and aid in the identification of those with amnesia or those that have died whose identity is unknown. Fingerprints also can be of use in background checks for many purposes, from government employment to getting a firearms license.
Law enforcement investigators, analysts and forensic scientists use fingerprints to identify potential suspects, victims and witnesses alike, to aid in finding evidence for a criminal investigation. Through fingerprint identification, a suspect in a crime may appear in a law enforcement database as the perpetrator of other crimes. Fingerprints are the first step of identification in the absence of DNA to verify an offender's identity, past arrests and convictions, known associates and other information useful to the investigation. These records help in court cases and later, in deciding criminal sentencing.
Characteristics of Fingerprint Locations and Visibility
After contact, fingerprints can remain on a solid surface, including the human body. Fingerprints fit into one of three categories according to what type of surface they are on and if they are visible or invisible:
- Latent prints. Invisible fingerprints made from sweat and oil on the surface of the human body.
- Patent prints. Prints formed when dirt, blood, ink, paint and other liquids come into contact with fingertips, then transfer to a solid surface. Patent fingerprints can be seen with the naked eye.
- Plastic fingerprints. Three-dimensional, easily seen prints on soft surfaces, including wax and wet paint.
Fingerprint Pattern Groups and Characteristics
Friction ridges, or raised skin, and furrows, or recessed skin, make unique fingerprint patterns that appear on the digits and thumbs of each hand. Within fingerprints are delta points, or patterns that look like the Greek letter of the same name. The delta point is the point where two parallel ridge lines converge. Fingerprints also have core points or center areas. Depending upon the type of fingerprint you have, it may have more than one delta, more than one core or none at all. Patterns made by friction ridges are in three distinct groups: loops, arches and whorls. Within each group are variations or subgroups for a total of nine fingerprint patterns.
Patterns of Loop Fingerprints
Loop fingerprints are the most common type of prints and are found in 60 to 70 percent of the population. Loop prints recurve upon themselves forming a loop shape. A loop fingerprint can start on either side of the finger. It curves up and around and exits on the same side from which it entered. Determination of loop fingerprints relies on the bones in the forearm, where the loop begins and ends, and on which hand the prints come from, since loop fingerprints show up in reverse on either hand. Loop fingerprints come in three variations:
- Radial loop. This type of fingerprint shares its name with the radius bone, located in the forearm under the thumb. Radial loop patterns run toward the radius bone and thumb. Radial loops are uncommon and usually found on the index fingers of the hand.
- Ulnar loop. This variation of fingerprint runs in the direction of the ulna bone located in the forearm underneath the little finger.
- Central pocket loop. The ridges of this composite fingerprint form a loop pattern that recurves around a central whorl.
Variations of Whorl Fingerprints
Whorl patterns contain two or more deltas and occur in 25 to 35 percent of the population. A whorl-patterned fingerprint consists of nearly concentric circles. A whorl fingerprint's ridges can make a turn through at least one circuit. There are four variations of this type of print:
- Plain whorl. A plain whorl has one or more ridges that make a complete circuit. This type of whorl also has two deltas with an invisible or imaginary line that touches or crosses at least one recurving ridge within the inner pattern area.
- Central pocket whorl. This whorl pattern has one or more recurving edges or a right-angle obstruction to the line of flow. This obstruction has two deltas with an invisible line in between, but no recurving ridge within the pattern is cut or touched. The ridges in a central whorl pattern complete a full circuit and may be any variation of a round shape, including a spiral, oval or circle.
- Double loop whorl. Two separate, distinct loop formations make up a double loop whorl pattern. This variation of a whorl fingerprint has two different shoulders for each core, two deltas and one or more ridges, all of which make a complete circuit. Between the loop formations is at least one recurving ridge within the inner pattern area. This ridge is cut or touched by an invisible or imaginary line.
- Accidental whorl. Accidental whorls combine two or more different types of subgroups – the only one that does not apply in this combination is the plain arch – have two or more deltas and contain ridges matching the characteristics of a whorl subgroup.
Types of Arch Fingerprints
Approximately 6 percent of people exhibit an arch fingerprint pattern. Within this group, lines cross smoothly or are upthrust at the center of the finger pad. The two types of arch patterns are:
- Plain arch. The plain arch is the simplest fingerprint of all. The ridges of a plain arch form on one side of the pad, rise in the center of the pad, then exit the other side. A plain arch fingerprint pattern often resembles a wave.
- Tended arch. The pattern of a tended arch follows that of a plain arch in that it forms on one side, rises and exits on the other side, but that is where the similarities end. Unlike the plain arch, the ridges in the center converge upon each other as they thrust upward. Instead of looking like a wave as they do in the plain arch, they resemble a pitched tent.
Surfaces and Collection Methods of Fingerprints
A fingerprint analyst employs different means to collect fingerprints based on the characterstics of a surface and whether it is porous, nonporous smooth or nonporous rough. Porous and nonporous surfaces differ in how they absorb liquids. If a surface is porous, the liquid sinks but if it is nonporous, the liquid stays on top.
For locating prints on a porous surface, an analyst sprinkles chemicals on the area in question, then photographs it in hopes of finding the hidden fingerprint. For surfaces that are nonporous smooth, experts brush for prints with powder and use lifting tape to pick up the print. Surfaces that are nonporous rough get the same treatment, but the analyst will employ the use of a gel-lifter or a silicone casting material, instead of lifting tape, to pick up the print.
Examination and Research of Collected Prints
After collecting fingerprints, an examiner can begin analyzing them to determine if there is enough information contained within the prints to make a possible identification. Determination of class and individual characteristics of a print will narrow it down to a group, but not identify a specific individual to whom it belongs. After initial analysis and classification, the examiner compares a known fingerprint from a potential suspect to the unknown print from a crime scene.
If class characteristics between the known and unknown print do not match, then the examiner eliminates that known print and may use additional known fingerprints for comparison. However, if class characteristics do match, the examiner then looks deeper at individual traits, focusing on the prints point-by-point until there is a potential match. After comparing known and unknown prints, the examiner can make a proper evaluation.
Evaluating Fingerprint Comparisons After Examination
An examiner can reach three conclusions when analyzing fingerprints: exclusion, identification and inconclusive. Differences between known and unknown fingerprints that exclude the known print as the source produce a determination of exclusion. However, if class and individual characteristics in the known and unknown prints align and there are no unexplained differences between the two, identification is the conclusion. If there is not enough detail in the known and unknown fingerprints with which to make a comparison, the examination is said to be inconclusive. An inconclusive fingerprint examination will not yield information as to whether the two prints came from the same source.
A second examiner then verifies the results of the first. The second fingerprint examination takes place independently from the first but employs the same steps. Both examiners must agree on their findings for a conclusion of identification. If they agree, this conclusion makes the fingerprints left behind at a crime scene a substantial piece of evidence.