Fingerprinting: An Analysis of Forensic Methods

Abstract

Fingerprinting has been a mainstay of North American forensics since the early 20th century. Fingerprints form on hands so early that the movement and pressure inside of the womb varies the patterns. This variance in each environment causes the fingerprint pattern to not only be unique to a particular individual but also from finger to finger. As paper and ink remain at the heart of the practice, Moore’s law will increase the speed, portability, and efficiency of fingerprint analysis through advancements in optical processing scanners, storage, and network connectivity. This paper overviews the history of fingerprinting and introduces contemporary practices of collection, visualization and analysis of forensic fingerprinting.

Keywords: fingerprinting, forensics, optical scanning, laser ablation, ridge pattern, friction ridge

Fingerprinting Analysis

Fingerprinting analysis has evolved into a powerful tool of forensic scientists throughout the world. Even as a ubiquitous and longstanding practice, the logistics of fingerprinting analysis are still plagued by inefficiencies and a lack of standardized analytical practices but technological advancements will continue to be a boon to the science of fingerprinting and the greater forensic community.

Types of Fingerprints

There are three types of fingerprints; latent, plastic, and patent. Huynh and Halamek (2016) explain latent fingerprints as the residual unique impressions which occur when the friction ridges of a finger pad come in contact with a surface, leaving behind loops, whorls, and arches in residue consisting of natural oils and skin cells which are not easily seen by the naked eye.

According to Axelrod & Antinozzi (2003), plastic fingerprints are impressions in a soft material such as wax, tar, or soap. Patent fingerprints result from one substance transferring to another surface, such would be the case with a muddy fingerprint on a wall (Axelrod & Antinozzi, 2003, p. 162). Plastic and patent prints may be readily photographed for examination, whereas latent fingerprints are more difficult and must be exposed and collected using numerous and evolving forensic methods. (Spaulding, 2008, p. 27).

Anatomy of a Fingerprint

Fingerprint patterns are divided into 3 overarching classifications; arches, loops, and whorls. Axelrod and Antinozzi (2003) explained the Federal Bureau of Investigation (FBI) subscribes to a system of nine basic fingerprint patterns used to winnow the search results among a group of potential matches. These nine patterns are classified as plain arch, tented arch, plain loop (right), plain loop (left), simple whorl, central pocket loop, lateral pocket loop, twinned loop, and accidental whorl.

Between 60 to 65% of the population’s fingerprint types are classified as loops. This pattern is characterized by one or more ridges entering from one side, curving around, and exiting on the same side. Subsets of the loops include the plain loop (enters and exits on the right), the central pocket loop, lateral pocket loop, and the twinned loop.

About 5% of fingerprints can be classified as arches. Arches are characterized by a ridge pattern originating on one side, riding to a peak or arch, and exiting on the opposite side. The arch pattern can be further divided into two subcategories, plain and tented.

Lastly, whorl patterns are circular with no defined entrance or exit of ridges and can be simple or accidental. A simple whorl has only the circular pattern visible and the accidental whorl shows two deltas where two lines run side by side then diverge with a significant curved line which passes in front of the delta (Axelrod & Antinozzi, 2003, p. 164-165). After a fingerprint is classified in this manner, a fingerprint expert then uses specific identification points and minute features to pair evidentiary prints with databased prints. The minute features used for this purpose include, “islands (small enclosed ridge patterns), dots (isolated dots rather than ridge lines), bifurcations (ridges that diverge or fork in various ways), and ending ridges (ridges that don’t connect, but simply dead end). ” (Axelrod & Antinozzi, 2003, p. 165)

Individualization

Fingerprints are formed on hands before birth and while the chance of having generalized fingerprint patterns may correlate to genetic inheritance, “the development of friction ridges also occurs so early that the movement and pressure inside of the womb would vary the patterns” (Huynh & Halamek, 2016, p. 328). This variance in each fingerprint pattern is therefore not only unique to a particular individual but also from finger to finger. While fingerprints are known to uniquely identify individuals throughout recent history, fingerprint analysis still lacks standardized guidelines for cross-identification. Practitioners generally follow their own thresholds of pattern identification matching based on 8-12 friction ridge feature matches (Huynh & Halamek, 2016, p. 329, ).

History of Fingerprinting

According to Leo (2015), the earliest known use of fingerprinting for identification purposes was in China in 650 AD. The Chinese appended prints to contracts, as described by historian, Kia Kung-Yen. In 1685, professor Marcello Malphighi employed the use of a microscope to observe the structure of friction skin. Then in 1788, a book on human anatomy by Dr. J. C. A. Mayer included illustrations of fingers and commentary on the absolute uniqueness of fingerprints, referred to as “the arrangements of skin ridges”. The year 1823 brought about the classification of fingerprint patterns into 9 categories, by a Czech Professor of Anatomy, Dr. J. E. Purkinje. Between 1856 and 1897, a German anthropologist by the name of Hermann Welcker, conducted a 34 year study on the permanence of friction ridges. In the Late 1800’s, Sir William Herschel of England, while a Magistrate in India, deployed the use of fingerprints for identification purposes. Herschel concluded that fingerprints did not show the slightest difference even when compared 57 years later. In 1880, Dr. Henry Faulds’ letter to the scientific journal, Nature concluded that criminals could indeed be identified from fingerprints found at crime scenes, such as those made in blood. In 1883, Alphonse Bertillion developed an identification system of Anthropometry, referred to as Bertillionage, which used body measurements to differentiate between individual humans.

Anthropometry was later phased out and replaced with a similar concept of biological uniqueness, fingerprinting. In the 1890’s, Sir Francis Galton, a specialist in genetics and biological variation published the first book on fingerprints. Galton’s volume cemented the “Galton Details” or the major ridge characteristics of bifurcation, ridge ending, island, and enclosure. Galton also performed a statistical study on the uniqueness of fingerprint patterns, which concluded the chance of duplicate fingerprints was 1 in 64 billion. Notably, this statistical analysis was reviewed in 1995 and found valid (Leo, 2015). The first case to introduce not only fingerprints into evidence but bloody fingerprints, occurred in 1892 by Juan Vucetich of Argentina. Shortly after, in 1897, Sir Edward Henry developed a system of classification for the storage and retrieval of fingerprint sets. According to Daluz (2014), in 1903, the New York State Prison System began to fingerprint inmates.

One year later, New York worked with Scotland Yard to present their fingerprinting research at the World’s Fair to other North American law enforcement agents (Daluz, 2014). 1915 brought about the first professional organization of fingerprinting, the International Association for Criminal Identification which was later renamed the International Association for Identification. In 1924, the Federal Bureau of Investigation’s identification Division was established by J. Edgar Hoover. As populations and crime grew in the United States, the previous methodologies for small scale fingerprint databases began to fail. The rise of digital computing in the 1960’s and 1970’s, paved the way for the Automated Fingerprint Identification System (AFIS) and its ability to digitize, allowing for storage and search-ability of large volumes of fingerprint records. The AFIS stratagem was exported to Europe and Asia and is still in use. (Daluz, 2014, p. 23-25).

Collection of Known Prints

Ink is the most widely known media for collecting fingerprints. With this method, a thin coat of ink is applied to the friction ridges of the finger, which is then pressed on a piece of paper. Much like a rubber stamp, a pattern is transferred to the paper due to the ridges and valleys present on the finger. The paper used in this process is referred to as a fingerprint card.

Optical Scanning

Optical finger scanners work similar to photo scanners and use the same sensor as a digital camera (CCD). The finger scanner also contains a light source to illuminate the ridges. As a finger is placed on a glass plate, a camera takes a picture of it, which creates an inverted image where darker areas represent the ridges of the finger and lighter areas are representative of the valleys. After the image is scanned, it will likely be used to compare against a database. One methodology for digital comparison of prints is where a computer identifies the minutiae points of a scanned image and uses a mathematical algorithm to store the fingerprint data in computer code as a reference. This reference data may then be compared to other prints in the future. (Girard, p. 151-153)

Contemporary Methods of Forensic Fingerprint Collection

Patent prints, or those that are visible, are collected using high resolution photography with a measurement scale for reference. This method may also use dye or chemicals or alternative light sources to increase the contrast of the print.

Dusting

Latent prints are most commonly collected via dusting. Dusting is a process of visualizing latent fingerprints on smooth, hard surfaces such as glass, tile, and painted wood by sprinkling a fingerprint powder onto the printed area. Fingerprint powders stick to the oily residue which are photographed and lifted from the surface with a clear adhesive tape which is transferred to a card for preservation. (NFSTC, 2013, p. 6)

Alternate Light Source

Laser or LED lights that emit a particular wavelength are used with different filters to provide visibility of fingerprints in order for them to be photographed. Sometimes the prints may be further processed with powder or dye after detection on likely surfaces such as doorknobs and windows. (NFSTC, 2013, p. 7)

Chemical Processing

Chemicals may be used to visualize latent prints located on porous or soft surfaces such as cloth or paper. According to Axelrod & Antinozzi (2003), the following chemical processes are available:

• Iodine - vapors can be used to stain the invisible print brown via a chemical reaction with skin oils. This process is performed in a fuming cabinet in a lab or with a fuming gun used at the crime scene or on items too large for a cabinet. Iodine fuming results must be photographed and documented immediately as they will fade quickly.
• Ninhydrin - a chemical that reacts with amino acids in fingerprints and visualize prints after the prints are dipped, sprayed, or brushed onto evidence. After 2 hours at room temperature,
• Silver Nitrate - produces a red-brown print by reacting with the salt in a fingerprint. A silver nitrate and alcohol solution may be sprayed onto evidence or the evidence may be dipped into the solution to provide an image for a very short time, which must be immediately photographed and documented before fading. (Axelrod & Antinozzi, 2003, p. 163-164)
• AccuTrans®- a liquid casting compound that fills the ridges of fingerprints may be used on textured surfaces to lift powdered latent prints (NFSTC, 2013, p. 9).
• Amido Black – a chemical that reacts with any protein, used for developing bloody impressions on skin (NFSTC, 2013, p. 9).

Limitations of Fingerprinting Techniques

According to the National Forensic Science Technology Center (2013), three factors are limited by current fingerprint analysis techniques; matching, timing, and DNA fingerprinting. Fingerprints must be matched to a known set of prints on file.

Without a robust database, prints can only be used to rule out individuals in an investigation. Additionally, there is no way to determine the time at which a print was deposited onto a surface. It is also not possible to determine sex, age, or race from a latent print. There are capabilities, if sufficient DNA is available from the print, from which sex can be determined. (NFSTC, 2013, p. 12). Before the digital age, fingerprints were collected by law enforcement agencies to report arrest information to state repositories and the FBI (GAO, 2004, p. 4). Due to the mail in process, submissions and responses to the FBI were lengthy. The GAO (2004) report found the following: “The process was time-consuming, given that the local arresting agency mailed the fingerprint cards to the state repository, which mailed the information to the FBI—and, in return, the FBI’s response (based on a search of national records) would be mailed back to the state repository, which would then mail the information to the local arresting agency. ” (p. 4)

While the implementation of paperless fingerprinting was a logical and vast improvement of speed and volume of prints processed, the GAO (2004) reported: “For the recent 8-month period we studied (October 2002 through May 2003), the overall average submission time for criminal fingerprints was 40 days (an average that encompasses both manual (paper) and electronic submissions)—whereas prior to the implementation of IAFIS, average submission times were significantly higher (e. g. , 118 days in 1997). ” (p. 3)“Nationally, there is no standard requirement regarding the types or categories of criminal offenses for which fingerprints must be taken by local and state law enforcement agencies, nor is there any standard time frame requirement (after the arrest) for submitting the fingerprints to state criminal history repositories. However, according to FBI officials, virtually all states require the fingerprinting of persons arrested for serious offenses. Also, according to FBI officials, the time frame requirement for submitting the fingerprints to criminal history repositories varies among the states—generally ranging from a specific number of hours or days to a nonspecific standard such as “promptly” or “without undue delay. ” (p. 7)

Emerging Methods in Fingerprinting

Laser ablation was first applied to fingerprinting by Eden Camp, an intern at the Louisiana State Police Crime Lab in 2015. Camp brought her idea to the Louisiana State University Department of Chemistry where researchers devised a way to use the lab’s lasers to lift fingerprint materials from a surface, suck them into a filter, and then use a spectrometer to analyze the contents. The contents could include lipids, proteins, genetic material (DNA), or any other relevant substances such as explosive residue (gunpowder etc. ). The method works by focusing a laser with mirrors onto a fingerprinted surface. Any moisture present on the surface is heated by the laser into a gas which lifts the molecules from the surface in a process known as laser ablation. The molecules are vaccumed into a filter and are examined by a mass spectrometer. A mass spectrometer is a device capable of analyzing ions in order to identify their elemental signature or chemical compound. This method has proven successful on porous and non-pourous surfaces such as glass, plastic, and cardboard. Future work on this project will be related to creating a portable apparatus for use in the field.

Possible Future Advances in Fingerprinting

As technological advancement continues along the path of Moore’s law, ( a prediction made by American engineer Gordon Moore in 1965 that the number of transistors per silicon chip doubles every year) we will see processing time of uploading and downloading fingerprints into databases to continue to increase. The technologies related to optical processing; scanners, storage, network connectivity, and increasing portability of devices, will make for the optical scanner devices to be more accessible to smaller and more remote law enforcement entities. The increased speed and accessibility with input and output of fingerprints will likely facilitate retention of known criminals. This advancement will also relate to portable devices for use in the field at crime scene locations. Field equipment and visualization techniques could lead to an increase in prints collected on scene. Biometric access will increase into more everyday items beyond mobile phones and laptops to items such as homes and vehicles. Undoubtedly, the increase in biometric access will lead to advancements in identity theft.