Fingerprint Analysis in Forensics: History, Methods & Limits

Introduction

The unique characteristics and contours of the fingerprint were first noted by 17th-century anatomist Marcello Malpighi, who highlighted the spirals and ridges of the fingerprint and after whom the Malpighi layer is named. Some two hundred years later, fingerprinting as a means of identification was practiced by an English administrator in India. It was not long before fingerprinting became a primary way of identifying and databasing information about a person's unique physical characteristics. Fingerprint analysis in the field of forensics was a staple of criminal justice by the middle of the 20th century, with the FBI in possession of 100 million fingerprint cards, which could be read by the Automated Fingerprint Identification System and kept on digital drives (Hawthorne, 2008). This paper provides background on the history of fingerprint analysis, how the process is conducted today, and the major controversies surrounding the practice in the field of forensics.

Historical Background

Fingerprint analysis has been used to identify individuals since the 19th century, when a British administrator in India, Sir William Herschel, required civil contractors to provide both signatures and fingerprints (Herschel, 1916). By 1880, Dr. Henry Faulds had published an article on fingerprinting in the journal Nature (Reid, 2003). Two years later in France, Alphonse Bertillon devised the Bertillon System of classifying identification measurements based on body dimensions such as height and limb length — a system that would be used for classification purposes until fingerprinting proved a better option.

In 1891, the practice of fingerprinting criminals was adopted in Argentina, and in 1892, Sir Francis Galton published a book in England arguing that fingerprints are unique to every person — a claim that has never been substantially verified by scholarship. In 1901, Sir Edward Henry, working in India, instituted the world's first systematic classification of fingerprints, which was eventually adopted by the United Kingdom and spread throughout the rest of the world. In 1903, the value of fingerprinting as a formal classification tool became apparent when two inmates at Leavenworth prison shared the same name and the same Bertillon measurements. Fingerprint identification was seen as the best method of distinguishing individuals, and two years later the U.S. military began using soldiers' fingerprints for that exact purpose. Law enforcement agencies soon followed, and the first fingerprint card was put into use in 1908 in the United States. Zabell (2005) has, however, noted that while reliability of fingerprint identification and verification is attainable, validity remains a concept the field has yet to achieve with consistency.

Process of Fingerprint Collection

Because skin produces an oily residue that can be left behind on physical surfaces, fingerprint impressions can essentially be deposited on any solid surface. Prints can also be left behind when any residue — such as blood, ink, or dirt — is present on the fingers when they come into contact with a surface. Fingerprint analysts can retrieve prints from soft surfaces such as soap or wax, as well as from flat, hard surfaces such as glass, wood, and walls, whether the prints are patent (visible to the eye) or latent (invisible). Latent prints can be recovered from a wide range of surfaces, from paper and cloth to metal and plastic. To recover latent prints, the analyst must apply fingerprint powder, which adheres to the oils deposited by the fingers upon contact with a surface, rendering the print visible. The print can then be copied for databasing and indexing to determine whether a match can be made and an identity established (NFSTC, 2013).

For patent prints, the collection method is photographic. High-resolution photography combined with a forensic measurement scale is used. Lighting and dye may sometimes be applied to enhance the visibility of the print, though this is often unnecessary. Latent prints are either dusted or developed using cyanoacrylate vapors, which cling to the oil residue of prints on non-porous surfaces without disturbing the crime scene. Once discovered, prints are photographed and lifted using adhesive tape.

Light sources have also become increasingly common tools for identifying fingerprints while preserving the crime scene. Blue lights with orange filters are one method forensics teams use to identify latent prints on solid surfaces (NFSTC, 2013). The forensics team is not limited to any single method; if one approach is not suitable, a variety of others can be employed.

For porous surfaces, prints are obtained using chemicals such as ninhydrin, which reacts with amino acids and inorganic salts left behind when fingers touch a porous surface. The chemical turns the prints purple, allowing them to be photographed. Prints can also be obtained from skin or clothing using methods such as Amido Black or vacuum metal deposition.

Once prints are found, they are uploaded to a computer database for indexing and matching. Local, state, and national databases assist investigators in determining whether the prints belong to anyone whose fingerprints are already on file. Today, algorithms assign similarity values to potential matches. Prior to computerization, prints were manually filed and classified according to ridge patterns that were also assigned values. These classifications include the arch, loop, whorl, and tented arch structures, according to the Henry (1900) classification system.

Conclusion

Fingerprint analysis goes as far back as the 17th century, when the ridges of the fingerprint were first examined by an anatomist in Italy. Since then, the fingerprint has become a source of particular appeal for forensic analysts, based on the assumption that no two fingerprints are alike. Fingerprint analysis has proven helpful in many cases over the decades since its adoption by law enforcement in the 20th century. However, it has never been a foolproof practice, nor does it carry a perfect record. There have been numerous instances in which prints lifted from a scene were used to convict someone who was not present. There have been cases where prints that appeared to match were used to imprison individuals against whom no other evidence existed.

Fingerprint analysis depends on the matching of small ridges and whorls, and the difficulty often lies in the complexity of those features on the human finger, as well as the challenge of recovering a clear print for analysis. The better the quality of the print, the more accurate the reading and matching can be — but in practice, recovering high-quality prints, even with all the technological resources available to investigators today, is not always as straightforward as it sounds. For that reason, caution is advised by the National Academy of Sciences, which rightly urges that fingerprint analysis be treated as one investigative tool among many, rather than as a definitive proof of identity or guilt.

References

Hawthorne, M. (2008). Fingerprints: Analysis and understanding. Boca Raton, FL: CRC Press.

Henry, E. R. (1900). Classification and uses of finger prints. London: George Rutledge & Sons, Ltd.

Herschel, W. J. (1916). The origin of finger-printing. Oxford University Press.

Innocence Project. (2018). Fingerprint analysis. Retrieved from

National Academy of Sciences. (2009). 'Badly fragmented' forensic science system needs overhaul; evidence to support reliability of many techniques is lacking. Retrieved from http://www8.nationalacademies.org/onpinews/newsitem.aspx?RecordID=12589

NFSTC. (2013). Fingerprint analysis. Retrieved from http://www.forensicsciencesimplified.org/prints/how.html

Reid, D. L. (2003). Dr. Henry Faulds — Beith Commemorative Society. Journal of Forensic Identification, 53(2).

Zabell, S. L. (2005). Fingerprint evidence. Journal of Law and Policy (Brooklyn College Law School), 143–77.