Edmond Locard was the founder of the Institute of Criminalistics at the University of Lyon in France. Locard believed that that when on person came in contact with another person or object a cross transfer of minute particles occurred. This theory became known as the “Locard Exchange Principle”. Locard believed that crimes could be solved by inspecting the “dust particles” carried to and from a scene. This science is known today as criminalistics and has led to the rise of the forensics laboratory (from Mount Royal College background notes FORE 4407 section 3: Unit 4) Francois Goron, head of the French Surete, seems to be one of the first modern investigators who tried to use hair to identify a killer. In his first case hairs found clutched in a dead woman’s hand could not be identified as human simply because there was no information on the subject.
The inability of the scientific community to distinguish between animal and human hair raised interest in the analysis of hair. In the years that followed researchers began to collect information about the structure of human and animal hair (Block, 1979). In 1899, several years after his original failure, in a case known as “L’affaire Gouffe” Francois Goron was able to establish that a murder victim’s hair had been dyed. Establishing this simple fact led to the identification of Gouffe’s body and subsequently to the arrest of his killers (Block 1979). Francios Goron had successfully used forensic hair examination to solve a crime.
The success of this case and others has led to extensive research into the nature of hair and how it can be used in forensic investigations. In this article I will attempt to cover some of the basic information regarding the collection and use of hair as forensic evidence. Hair must never be used as the sole indicator of guilt. Visual comparison alone is subjective and open to interpretation of the individual scientists. However, when hair is used in conjunction with D.N.A. and other evidence it can be a powerful tool for an investigator.
Hair is in all likelihood one of the most common types of trace evidence (Nickell, J. & Fischer, J. 1999). Hair is extremely variable among both individuals and racial populations (Crocker 1999) (Saferstein, 2004) (Greenshields & Scheurman, 2001). Great care must be used in the use of hair as evidence. Hair may in some cases rule out certain populations or help identify an unknown victim (Block, 1979). Cross transfer of hair from a victim to a suspect or vice versa may substantially raise the probability that the victim and perpetrator were in contact (Cocker, 1999). However, it can never be used as the so called “smoking gun” which would prove a person’s guilt. As with most forensic evidence the information obtained from hair is expressed in terms of probabilities of a match rather than an absolute match (Crocker, 1999).
Collection of Evidence
Methods of collecting hair evidence vary according to the scope and the circumstances of the investigation (Greenshields & Scheurman, 2001). In some circumstances more than one method of collection will be utilized. In general the methods of collection hair as potential evidence have not changed since the last quarter of the 19th century (Bisbing, 2001).
There are six main methods of collection. The first is collection of visually observed hairs. The investigator may collect visual observable hairs by hand or with tweezers. The use of tweezers is not recommended in most cases because they can cause damage to the structure of the hair. Tweezers can also crush the delicate root structure and surrounding tissue which is used in D.N.A. analysis (Greenshields & Scheurman, 2001) (Bisbing, 2001) Forensic light sources such as infrared or laser may be used to enhance the ability of the investigator to visually identify hairs (Greenshields & Scheurman, 2001) (Crocker, 1999) Clear tape can be used to lift both visible and non-visible hair from a variety of surfaces. In Canada this is the most widely used method (Crocker, 1999) Clear tape can be used in either a roller type form or as sheets. When sheets or squares are used on a garment each section will be labeled as to which part of the garment the samples were obtained from (Bisbing , 2001) It is important that the tape is not so sticky that it becomes clogged with fibres from then garment or material it is used on (Crocker, 1999).
Vacuuming method of collection used for large crime scenes or where the most likely points of transfer or unknown. Vacuuming can also be used on stationary objects which cannot be transported (Greensheilds & Scheurman, 2001). The vacuums used by investigators are fitted with a special filter which can be removed and labeled appropriately. (Crocker, 1999)
Another method of collection is brushing, scraping or shaking of garment or other cloth objects. The material being examined is held over a white sheet of paper and abraded in order to dislodge and hair adhering to it (Bisbing, 2001) Trace evidence found on the white paper is then separated into classes such as hair, fibre, glass etc. and analyzed accordingly. This method is the second most commonly used method in Canada for the collection of trace evidence. (Crocker, 1999)
Some garments and other fabrics may be placed in a bag and agitated. This method allows the investigator to collect the evidence at the bottom of the bag rather than have it disperse into the air (Bisbing, 2001).
Finally, when collecting hair evidence combing and clipping are methods used. When looking for cross transference of hair (usually pubic) from a suspect to a victim or vice versa combing is used to extract loose hairs (Greenshields & Scheurman, 2001)( Bisbing, 2001) (Saferstein, 2004) Anyone who may have left hair at a crime scene should be sampled for comparison purposes. Approximately 100 scalp hairs from various areas of the head should be pulled and combed. Pubic and other body hair can be pulled, clipped and combed. Approximately 30-50 hairs should be collected and labeled as to the body area of origin and the method of collection (Greensheilds & Scheurman, 2001) (Bisbing, 2001) (Saferstein, 2004).
Structure of hair
A hair sample is analyzed as a whole and in cross section.
When viewed as a whole a hair consists of three parts. These three parts are the root, the shaft and the tip. The length and the shape of a hair can be used to identify the place on the body from which it originated (Innes, 2000) Sites of origin are considered to be the scalp, eyebrow , beard, underarm, body and pubic region (Lane, 1992) Some researchers also include ear hair as a separate region of origin (Crocker,1999)