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This article incorporates, in modified form, material from the not-yet-published Illustrated Guide to Forensics Investigations: Uncover Evidence in Your Home, Lab, or Basement.

 

Hair is one of the most common and useful types of trace evidence, particularly in crimes such as assaults, rapes, and murders. Humans shed hair naturally, on average about 100 hairs per day. Even casual contact between two people ordinarily results in each of them transferring some hair to the other, and during a violent confrontation the probability of hair being transferred from the victim to the attacker and vice versa is very high.

Several aspects of hair make it a very useful form of trace evidence:

  • Hair degrades very slowly over time, so an old specimen is as useful as a recent one.
  • Hair is easily shed and easily transferred from person to person or from person to clothing.
  • Once transferred, hair often adheres persistently to the person or clothing to which it was transferred, so it is likely to survive until it can be collected by the forensic technician.
  • Unlike bloodstains and other gross evidence, hair is small, light, and can easily go unnoticed by a criminal.
  • Although, in the absence of DNA testing, hair is technically only class evidence, it possesses enough individual traits that it can often be characterized quite closely. For example, the color of a questioned hair may alone suffice to rule out a suspect.

Dennis Hilliard comments

Keep in mind that in some cases where a competent examiner may consider that two or more hairs have the same morphological characteristics and could have originated from the same source, DNA analysis has shown that they could not have originated from the same source. Project Innocence has used these results to discredit hair comparisons and this has reduced its value in court testimony. Hair analysis value in the lab is, as you state elsewhere, a screening tool to identify human versus animal origin and to exclude hairs from being DNA tested.

Questioned hair specimens may be collected at the crime scene by technicians, using vacuuming or other methods. But such specimens are also collected by forensic scientists in the lab, often from clothing or from a knife, club, or other weapon used in the commission of a crime.

Dennis Hilliard comments

Vacuuming for hairs and fibers is reserved for large areas such as vehicles. The vehicle is divided into sections, such as front right, front left, etc. The vacuum filter is changed for each section.

In this lab session, we’ll use two of the methods commonly used in forensics labs for obtaining hair specimens.

Required Equipment and Supplies

  • goggles, gloves, and protective clothing
  • magnifier
  • forceps or tweezers
  • specimen storage containers (see Substitutions and Modifications)
  • light source (see Substitutions and Modifications)
  • lifting tape (see Substitutions and Modifications)
  • transfer sheets (see Substitutions and Modifications)
  • permanent marking pen
  • clothing specimens (see Substitutions and Modifications)

All of the specialty lab equipment and chemicals needed for this and other lab sessions are available individually from the Maker Shed or other laboratory supplies vendors. Maker Shed also offers customized laboratory kits at special prices, and a wide selection of microscopes and microscope accessories.

sciRoomCAUTION2.gif CAUTIONS

Although none of the activities in this session present any significant risks, as a matter of good practice you should always wear splash goggles, gloves, and protective clothing when working in the lab, if only to avoid contaminating specimens.

Substitutions and Modifications

  • You can use any suitable container for storing specimens, including vials, pill bottles, stoppered test tubes, small paper envelopes, or small resealable plastic bags. Whatever containers you use should be labeled as soon as you transfer the specimen to them, either by writing directly on the container or attaching a label to it.
  • A high-intensity desk lamp or a similar strong, directional light source is ideal for a close examination of the clothing specimens. You want the light to strike the surface of the specimen at an angle, which helps reveal hairs and other material that is not a part of the fabric itself. Placing the light source so that light strikes the specimen at a grazing angle is best for revealing hairs and other traces adhering to the clothing.
  • You can use any transparent, colorless sticky tape as lifting tape. We used packing tape.
  • For transfer sheets, you can use any transparent, colorless sheets of plastic. We used the stiff clear plastic sheets used as packing material to protect the screens of our LCD computer monitors. You can also use transparent notebook page protectors, theater gels, overhead transparency sheets, or any similar plastic sheets. If the lifting tape is small enough, microscope slides can be used as transfer sheets. (Make sure enough room remains uncovered by the tape to allow the slide to be labeled.)
  • Obtain unlaundered clothing specimens. Some of the best potential sources of hair specimens are the interior of hats, scarves, the collar and underarm areas of shirts, and the crotch area of panties or pantyhose and underpants.

Procedure

This lab has two parts. In Part I, we’ll use a magnifier and forceps to extract individual hair specimens from clothing. In Part II, we’ll use sticky tape to lift hair specimens from clothing.

Part I – Obtain hair specimens with forceps

Depending on the type of fabric and the nature of the clothing, it is often best to extract hair specimens by using a magnifier and forceps as follows:

  1. If you have not done so already, put on your goggles, gloves, and protective clothing.
  2. Place the clothing specimen on a flat surface and direct the light source at a grazing angle across the surface of the clothing.
  3. Use the magnifier to examine the entire surface of the specimen thoroughly.
  4. When you locate a hair or other piece of trace evidence, use the forceps carefully to remove the specimen and transfer it to an evidence container, as shown in Figure 6-1. If there are many similar hairs, you can take only one or two of them as specimens, but be sure to continue examining the clothing specimen until you’re certain that no other types of hairs are present.
  5. As you transfer each specimen to its own container, initial and date that container and write a brief description of the contents. Include the clothing specimen number or description, the location on the clothing specimen from which the specimen was obtained, and any other pertinent information. Also log all information about the specimen in your lab notebook and/or Table 6-1, one line per specimen.
  6. Repeat steps 2 through 5 for additional clothing specimens, if applicable.

Figure 6-1

Figure 6-1. Using forceps to gather hair specimens from a clothing specimen

Part II – Obtain hair specimens with sticky tape

Although it’s generally preferable to extract hair specimens individually with forceps, there are times when using sticky tape to lift hair specimens may work better, particularly if the clothing has a rough texture. The other side of that coin, of course, is that using a tape lift often provides an embarrassing plethora of specimens, most of which are fibers from the clothing specimen itself.

Figure 6-2

One major advantage of the tape-lift method, shown in Figure 6-2, is that it may capture very small trace-evidence specimens that may go unnoticed under low magnification. Even if you use forceps to extract specimens manually, you should follow that with a tape-lift unless you’re absolutely certain that no useful trace evidence remains on the clothing specimen.

Use the following procedure to do a tape lift and to preserve the results:

  1. If you have not done so already, put on your goggles, gloves, and protective clothing.
  2. Place the clothing specimen on a flat surface. Spread it out and flatten it as much as possible.
  3. Remove an appropriate amount of tape from the spool, being careful to avoid contaminating it with random fibers or other extraneous material.
  4. Carefully place the tape sticky side down in contact with the clothing specimen, using the minimum amount of pressure needed to capture specimens from the clothing specimen. If the specimen cloth is smooth and hard-surfaced, very little pressure is needed to capture any specimens that are present. If the specimen cloth is rough and soft-surfaced, more pressure is needed (and correspondingly more of the cloth fibers will also adhere to the tape). Learning how much pressure to use is a matter of experience.
  5. Peel the tape away from the clothing in one movement and immediately press the tape against the transfer sheet until it adheres. Label the lift as shown in Figure 6-3. (In effect, the labeled lift takes the place of a labeled specimen storage container. You can subsequently remove individual hair specimens from the tape and examine them individually.) Also log all information about each lift in your lab notebook and/or Table 6-1, one line per specimen.
  6. Repeat steps 2 through 5 for additional clothing specimens, if applicable.

Figure 6-3

Figure 6-3. Labeling tape-lifted hair specimens on a transfer sheet

Table 6-1. Collect hair specimens – observed data

ID # Source Observations
example stocking cap numerous short (~ 20 mm) gray hairs on interior surface of cap
example stocking cap one medium (~35 mm) blond hair on exterior surface of cap
example stocking cap three long (~70 mm) black hairs (canine?) on exterior surface of cap
1    
2    
3    
4    
5    
6    
7    
8    
9    
10    
11    
12    
13    
14    
15    
16    
17    
18    
19    
20    

Real Life

The three example lines at the top of Table 6-1 are real data, from Robert’s stocking cap. The short gray hairs are his. The long black hairs are almost certainly either from one or both of our Border Collies or from Barbara, whose hair is naturally black. Barbara asked Robert who the blond hair belongs to. Uh-oh.

Review Questions

Q1: Can an individual hair found among the trimmings on the floor of a barbershop be individualized to the person from whom it originated? If so, how? If not, why not?

Q2: What are some possible disadvantages to using a vacuum to gather hair specimens?

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