Hair and fiber analysis

In forensics, the analysis of hair or fiber evidence found at a crime scene can often be very useful in linking a suspect or victim to a scene. Use of hair and fiber evidence in forensics was already well established by the early twentieth century, and was and is an important tool in any investigation. Hair and fiber evidence alone is typically not enough to make a conviction, but is nevertheless a useful asset in crime solving.

One of the first scientific papers on hair and/or fiber analysis was published in 1857. By the early twentieth century, the microscopic examination of hair and fabric fibers was firmly established in forensics.

Hair can be very useful in the identification of a suspect or victim. In humans, hair can be used to identify the race of a person, to general classifications of the Negroid, Mongoloid and Caucasian races. Aspects of a hair such as color, texture, width, and the shape of the root can be used to tell whether the hair originated from a human, it'sspecific race, or even matched to a particular individual.

A comparison of hairs of different races

Fibers can be collected from a scene in a number of ways. Sometimes it is possible to individually pick out a fiber, but this is not always the case. Many times it is more useful to use tools such as sticky tape or specialized vacuums to collect fibers from surfaces such as upholstery or other fabrics.

There are many types of fibers other then hair that could be used to aid an investigation. When a piece of fabric, such as a person's clothing, comes into contact with another object, it will typically leave small traces of the fiber it is constituted of. Cotton, wool, silk, hemp and many different varieties of synthetic fibers make up most clothing, and the fibers that said clothing sheds can be used to link persons of interest to a particular scene. Synthetic fibers such as nylon, rayon, or polyester are produced by extruding liquid which then cools and solidifies; as a result of this production method, the resulting fiber has a very smooth and even appearance when viewed under a microscope, similair to the natural fiber silk, whichis produced naturally in a similair way.

Various types of fibers as they appear under a microscope.

One particularly famous case in which fiber analysis was used to build a case was the case of the Atlanta child murders from 1979 through 1981. Police first identified Wayne Williams as a suspect in the case when a stakeout crew noticed him driving away from a bridge near which a loud splash had occurred, suggesting that he had dumped a body. The body of the 27 year old Nathaniel Carter was found two days later in the river, corroborating this theory. Police investigators discovered fibers on victims that matched with fibers from Williams' car, bedspread, carpets, and dog. Williams was convicted to two consecutive life sentences, and declared to be the culprit behind 23 of the 29 child murders that occurred in Atlanta from 1979 to 1981.

Fingerprint pattern classifications

Fingerprints are given three main classifications based on the general characteristics of their pattern, those being loops, whorls and arches.

The loop pattern is the most commonly occurring. In a loop pattern, one or more ridges enters on one side of the print, loops around, and exits on the same side it entered. There are two main types of loop patterns; the radial loop and the ulnar loop. The ulnar loop is the most common, and is characterized by the loop opening towards the little finger, opposite from the thumb. It is named after the ulna, the bone in the forearm that connects to the hand on the side of the little finger. The radial loop is identical to the ulnar loop with the exception that it opens towards the thumb; it is named after the radius, which is the bone in the forearm that connect to the thumb.

An Ulnar loop print pattern.

Whorls are less common then loops. Any pattern in which one or more ridges makes a complete circuit or circle is a whorl.

A plain whorl print pattern.

The least common variety of fingerprint pattern is the arch. An arch pattern is characterized by having each ridge enter one one side of the pattern, and exit on the opposite side so as that no ridge loops or turns back on itself. Often the ridges will turn upwards in theappearance of anarch, hence the name of the pattern.

An arch print pattern.

Types of fingerprints

In forensics, fingerprints are divided into three categories: direct, latent or plastic.

Direct prints are those that are intentionally laid down, typically using some type of ink that has been applied to the fingers or hands. Direct prints are used for record keeping purposes, such as for authentication on documents or for record keeping, such as when criminal's fingerprints are taken after they are arrested. Direct prints can be compared to latent or plastic prints to determine who deposited the plastic or latent prints in question.

Latent prints are prints that are laid down unintentionally, and are often difficult to detect with the naked eye. Prints such as these can be deposited any time someone's bare fingers come into contact with another object; the prints are often laid down due to the natural oils found on human skin, which are deposited following the pattern of friction ridges on the fingers. Since latent prints can be difficult to see and photograph, certain chemicals substances are used to make the prints appear more clearly. One method is to gently spread a powder onto the print, and then remove the excess powder; the remaining powder will typically adhere to the oils in the print, and reveal their pattern in a way that is more visible. If a print is laid down on a very light surface, a white powder is typically used, as it contrasts well with the dark background. Conversely, if there is a light or transparent background, a dark powder is used. Fingerprints can be also developed by other more advanced techniques, utilizing chemicals that may react to the oils in a latent print or chemicals that may emit light under certain circumstances.

Once a latent fingerprint has been found and developed, it can be photographed or lifted. Lifting a fingerprint is the action in which the developing agent, or powder that has been used to reveal the print, is lifted off the original print with a sticky surface, such as tape, and deposited on a mobile card for transportation and future reference. Lifting prints instead of simply photographing them can be useful when you wish to examine a print in greater detail at a later date or in a different location, such as a laboratory where more advanced techniques could be utilized to analyze the print.

Plastic prints are prints that have been imprinted into a soft medium so as to preserve the three dimensional shape of the original friction ridges. Plastic prints may be left in substances such as soft clay, wax, or putty. This type of print is considerably more rare then a latent print.

History of Fingerprinting

Fingerprinting has been used to identify a unique individual since antiquity. Fingerprints have been found on ancient Babylonian clay tablets dating to at least 2,000 BC, which were likely used as signatures on official documents. By around 300 AD, Chinese documents were often impressed with finger prints to serve as signatures, or sealed with wax containing an impressed thumbprint to protect against forgery.

The image above depicts fingerprints found impressed in an ancient Babylonian tablet.

In 1858, Sir William James Herschel, a British Magistrate in India, began using impressed fingerprints on contracts. Soon, Herschel noticed that no two persons had identical fingerprints, and thus that a fingerprint could be used to identify an individual. Herschel's private conviction of the practical applications of fingerprints contributed to their widespread use in law enforcement and jurisprudence.





 The image shown is of the contract and impressed handprint that Herschel first used in the authenticating of a contract.

In 1863, Paul-Jean Coulier, a french professor, published his observations that otherwise invisible (latent) fingerprints could be identified via certain chemical processes. This helps pave the way for the fingerprints widespread use in law enforcement for identifying suspects.


Dr. Henry Faulds, who recognized the significance of fingerprints, devised a classification system for fingerprints in the 1870s. In the 1880s, he sent Charles Darwin his findings and classification system. Darwin, in advanced age and a poor state of health, told Faulds that he could be of no assistance to him, but did pass the information on to his cousin, Francis Galton. Galton then published various research on fingerprints, and encouraged its use in forensic science in the book Finger Prints.

 
Henry Faulds.

In Argentina, in 1879, the first organized system of recording the fingerprints of individuals on file, based on Galton's pattern classifications, was developed.The first criminal case in which fingerprints were used to aid in an investigation was an 1892 murder case in which a bloody thumbprint was found on a doorknob. When compared with the suspect's thumb, the prints were found to be identical.

In the late 19th and early 20th century, many western nations such as the United Kingdom and the United States began keeping file of criminal's fingerprints, and using them in cases.
In 1902, a thief who had been previously arrested and had his fingerprints filed, broke into an apartment and killed a man. The thief and murderer left a fingerprint on a piece of glass, and this evidence was recovered and used to convict the suspect.


Today, fingerprints are recorded when a suspect is arrested, or when entering certain employment. Government organizations such as the FBI or the Department of Homeland Security, have databases of over 100 million sets of fingerprints. Computers are typically used to aid in the matching and identification of fingerprints. Many security systems utilize computerized fingerprint scanning technology to verify a person's identity.


 
A fingerprint scanner.