Friction Ridge Skin and Personal Identification: A History of Latent Fingerprint Analysis

In 1904, the World's Fair was held in St. Louis, Missouri. A special exhibit of the British crown jewels sailed from London for exhibit at the fair, sent by Queen Victoria of England. Naturally, such valuable jewels could not travel and display in the exhibition unguarded. Sergeant John Kenneth Ferrier of Scotland Yard traveled with this British treasure to ensure that no theft would occur. However, he brought more with him than the crown jewels. Ferrier knew about a new concept that had not yet traveled to America; fingerprints, classifying them, and how they could be used for personal identification . Ferrier was so committed to the potential of fingerprint identification that he shared his knowledge by holding demonstrations of fingerprinting techniques for foreign police chiefs gathered at the fair, and training several American police officials afterwards.

By the mid 1880s, fingerprints had been studied by Henry Faulds (1843–1930), a Scottish medical missionary in Tokyo, Japan; by William Herschel (1738–1822), a British chief administrative officer assigned in Bengal, India; and by Francis Galton (1882–1911), an English biologist and cousin to the British naturalist Charles Darwin (1809–1882). These men considered fingerprints to be both individual to each person and permanent throughout life. Faulds even considered using fingerprints for identifying criminals at a crime scene and had successfully done so. By the time of the World's Fair in 1904, the industrial revolution had peaked, and the world was awash with new technologies. Telephones were fairly usual, automobiles were becoming more common, and the Wright brothers had just made their successful flight at Kitty Hawk less than a year earlier. New ideas and technologies excited Americans. Fingerprints became an important feature in this new technological world. Additionally, palm prints and footprints could also be used for personal identification

The skin on the palmar surface of the hands and plantar surface of the feet is specialized. It is called friction ridge skin because the skin occurs in a corrugated fashion with elevated ridges broken up by lower furrows. In other words, this skin is not flat and smooth like other skin. Friction ridge skin is slightly elastic in nature and assists in gripping objects and surfaces.

Friction ridges form in the uterus by the fourth month of fetal development and remain unchanged and absolute for a person's lifetime, only decomposing after death. These unique factors make friction ridge skin ideal for use in personal identification. Once friction ridge skin was recognized as valuable and reliable for personal identification, different people began to work on systems for taking these prints and then organizing them. Faulds had previously used printer's ink to take the fingerprints of his subjects. In the early twentieth century, American chemical engineer John A. Dondero (1900–1957) developed new inks for the purpose of recording prints, including special ink for footprinting newborns. Edward Henry, with the assistance of two Indian civil servants, developed a system for classifying and filing mass quantities of fingerprint cards. This system is the one shared by Ferrier and is still known today as the Henry System. With the advent of automated identification systems, use of Henry's system has declined.

While prints could now be documented for future identification, how would prints left at crime scenes be used? As with other technologies, an application of other sciences began to play an increasingly larger role. Prints left at crime scenes or on items are generally referred to as latent prints. The word latent is from Latin and means to be hidden or not visible to the naked eye. Such a print is left as a result of a person touching a surface and transferring oils, perspiration, and other materials to the surface; or by the touch actually removing material from the surface. A print that is visible is called a patent impression. Patent impressions can be found in substances such as blood , motor oil, grease, or other contaminants left, for instance, on a wall or door frame. Prints or impressions left in a semi-soft substance like window putty or butter are called plastic impressions because they are molded in the substance. The vast majority of crime scene impressions, however, are latent impressions, and must be developed in some manner to make them visible. In the early half of the twentieth century, much work was done in inventing different colored powders that could be dusted on a surface to develop the print and make it visible for photography . It wasn't until much later that latent prints were actually lifted with a special tape and placed on a backing card with documentation.

Initially, the study of friction ridge skin involved the science of embryology and anatomy. The practice of photography obviously became more and more important, as did the use of magnifiers and specialized lenses. Additionally, with the development of inks and powders, chemistry began to play an everlarger role. By the 1950s, iodine was used for fuming evidential items in a chamber; and chemicals that reacted with amino acids (secreted in sweat) were used on porous items such as paper. This was only the beginning. By the 1980s, cyanoacrylate ester (more commonly known by the trade name of Superglue®) found its way into usage. Additional research brought the development of fluorescing chemicals that could be applied after cyanoacrylate ester. Next, physics found its place in latent fingerprint examination as lasers and other light sources allowed the application of different wavelengths of light to make such chemistry fluoresce (emit visible light), thus allowing for photography. Another role of physics involves utilizing high vacuum for coating items with metals such as gold and zinc in specialized vacuum chambers. Particular chemical and mechanical techniques continue to be developed each year for working with difficult surfaces such as adhesive tapes, human skin, distinctive plastics, and highly colored backgrounds. While some chemistry is especially effective on dry surfaces, other chemistry makes it possible to deal with wet surfaces. All these techniques optimize the opportunity to develop latent impressions on a wide variety of backgrounds and surfaces or substrates.

The 1990s firmly established the science of biometrics , which boomed with the improvement of computers and refinement of software programs. By the beginning of the twenty-first century, computers were able to scan fingerprints and palm prints, and store images of those prints in automated identification databases.

Once an impression is rendered visible, documented, and recorded; it must be compared with a known-recorded print of an individual in order to identify it. The recorded impression, whether inked or scanned, is considered an ideal impression. This is due to the fact that the print can be repeatedly documented to get the very best recording of the friction ridges. While computers can record and scan impressions, they can never make a positive identification. Computers only make tentative matches. Identification will always require a trained and skilled human being to make the physical comparison. Identification is established by analyzing, comparing, and evaluating the arrangement of friction ridge characteristics in the latent print to those in the known impression and finding a match to the exclusion of all other prints.

Forensic identification of latent prints is a specialized field of study that encompasses many sciences. Commitment to a career in this forensic science requires an understanding and application of the scientific method. Knowledge of the biological formation of friction ridge skin, the nature of this specialized skin, and an awareness of the various technologies and methodologies employed in developing latent impressions is also required. Of the utmost importance, a forensic scientist must have a solid sense of professionalism, including high personal ethics and integrity in assuming responsibility for forming qualified opinions of identification of individuals.

see also Biometrics; Fingerprint; Fingerprint analysis (famous cases); Identification; Integrated automated fingerprint identification system; Latent fingerprint; Superglue® fuming.