Hairs, Fibers, Crime, and Evidence, Part 3, by Deedrick (Forensic Science Communications, July 2000)
|
July 2000 - Volume 2 - Number 3 |
Hairs, Fibers, Crime, and Evidence Part 3: Crime and Evidence
Douglas W. Deedrick
Unit Chief
Trace Evidence Unit
Federal Bureau of Investigation
Washington, DC
Introduction | Crime Scene Search | Evidence Collection | Evidence Handling Procedures
Protocol for Evidence Processing in the FBI Laboratory
Examination Conclusions
The manner in which a crime scene is searched is determined by the type of crime, the location of the scene, details concerning events of the crime, the time of day, the number of people available for the search, and available equipment. Inasmuch as hair and fiber evidence can play a role in most cases involving violent crime, serious consideration should be given to collecting it properly. Once the crime has been committed, little time remains before hair and fiber evidence will be lost or contaminated. The importance of securing the crime scene cannot be overstated.
Crime Scene Search
When physical contact occurs between two individuals, objects, or individuals and objects, there is a likelihood of transfer of hair and fiber evidence. This likelihood is dependent on the nature of the contact, the duration of the contact, and the nature of the contacting surfaces. The direct transfer of hairs from the head of an individual to the clothing of another individual is called a primary transfer. When hairs have already been shed and are transferred to an individual, it is called secondary transfer. Fibers are transferred in a similar manner. When fibers are transferred from the fabric of an individual’s clothing to the clothing of another individual, it is called a primary transfer. As these same fibers are transferred to other objects during subsequent contacts, secondary transfers are occurring.
It is important for crime scene investigators to understand the mechanisms of primary and secondary transfer. As trace evidence can be transferred during the commission of a crime, it can also be transferred during the search process. Hairs and fibers can not only be picked up inadvertently by investigators, they can be inadvertently deposited at the crime scene. The following are considerations at the crime scene:
- Elimination hair and/or fiber samples may need to be obtained from personnel conducting the search.
- Prioritize the order of evidence collection. Collect large items first and then proceed to the trace evidence. USE CAUTION WHEN WALKING THE CRIME SCENE.
- Once the trace evidence is collected via vacuuming, taping, or tweezing, take blood samples, remove bullets, dust for fingerprints, and so on.
- Processing the crime scene for fingerprints prior to trace evidence collection is not recommended because it can
- Inadvertently transfer trace evidence onto the clothing of the technicians,
- Move trace evidence, and/or
- Contaminate trace evidence with dusting powder.
- Inadvertently transfer trace evidence onto the clothing of the technicians,
Evidence Collection
The following are suggestions for collecting evidence from crime scenes such as houses, apartments, and vehicles:
- Photograph all evidence prior to removing it.
- Remove larger items or debris from carpeting or walk areas prior to other examinations. Consider wearing disposable booties.
- Collect large items, such as clothing, and place them in separate paper bags. Keep an accurate evidence log. One person should collect and bag the items while another person labels the bags and records the items in the log.
- Do not place all clothing items from a suspect in one paper bag, nor all items from a victim in another bag. Bag each item separately.
- Never put suspect items and victim items in contact with one another. The person collecting the suspect’s items should not be the same person that collects the victim’s items. If this must occur, personnel must change their clothing and collect the evidence at a different time to avoid contamination.
- Bedding should be carefully handled to avoid loss of hairs and fibers. Each item should be placed in a separate bag.
- Floor surfaces should be vacuumed for possible trace evidence. Some crime scene investigators use tape to secure trace evidence; however, tape is generally difficult to work with at the scene and in the laboratory. Smaller surfaces such as chairs and car seats can be taped or vacuumed.
- Ensure that carpet, pet hair, and other standards that might have transferred to a suspect or victim are collected.
- Always process for fingerprints after collecting trace evidence.
- Collect all possible known fiber samples from a vehicle. These may be obtained from the carpet, door panels, headliner, seats, floor mats, and trunk.
The following suggestions pertain to different types of items recovered at the crime scene:
|
Hats: |
Package all hats in separate paper bags. Use care when collecting baseball-style caps with adjustable plastic headbands—the bands are an excellent source for fingerprints. | |
|
Shoes: |
Shoes are an excellent source of fiber evidence, blood stains, and shoe print comparisons. Shoes worn by a suspect can deposit fibers from a vehicle he or she exited at a crime scene and can also pick up fibers from the scene and then deposit them in another location. | |
|
Socks: |
Socks worn by a homicide victim can provide invaluable fiber and hair evidence. Many times the victim is transported by vehicle. Contact with the interior surfaces of a vehicle can cause hairs and fibers to collect on the socks. It may be necessary to obtain elimination samples of the carpeting of the victim’s car or residence to avoid the possibility of a coincidental match. | |
|
Fingernails: |
Use care when scraping or clipping the fingernails of a victim or suspect. DNA on the hands or tools of the medical personnel can contaminate the material and influence the DNA results. | |
|
Hairs in the |
Hairs found in the hands of the victim usually belong to the victim. Rarely are the hairs similar to the suspect’s known hairs; nevertheless, these must be collected and submitted for analysis. | |
|
Pubic and head |
Pubic and head hair combings should always be taken in violent crimes. Foreign hairs as well as fibers can be recovered from these samples. If a hat is recovered at the crime scene and a suspect is identified soon, it may be possible to find fibers similar to those in the hat in the suspect’s hair. | |
|
Known hair |
Thorough random samples should be taken from the head and pubic regions of a suspect(s) and victim(s). Twenty-five full-length hairs, pulled and combed from different areas of the head and pubic regions, are generally considered an adequate representation of an individual’s hair characteristics. |
|
|
Weapons: |
Weapons recovered at a crime scene should always be searched for trace evidence before processing for fingerprints. | |
|
Doors and |
Doors and windows should be searched for trace evidence if they are possible points of entry or exit. |
Evidence Handling Procedures
Once the evidence has been collected, there are several recommendations or considerations when packaging it for transmittal to the laboratory. Clothing items must be packaged in separate sealed paper bags—not plastic. To avoid contamination, clothing items from the suspect should never be handled in the same area in which items from the victim are handled. All damp or blood-soaked items must be air-dried in a room away from air movement and traffic. Drying paper placed under damp clothing items should be submitted separately.
Submit individual hairs and fibers in clean paper or in an envelope with sealed corners. The primary paper or envelope should be placed inside a secondary sealed envelope with all corners taped. Many times individual hairs identified on items of clothing are not removed or secured. These hairs may move or be lost, so it is recommended that they be removed and placed in an envelope (first noting where they were removed).
If a floor surface is vacuumed, the debris should be placed on a white sheet of paper (8 x 11 inches) and folded at the corners. This paper should be placed in a heat-sealed or resealable plastic bag.
Protocol for Evidence Processing
in the FBI Laboratory
|
When evidence is received in the Trace Evidence Unit, the case is assigned to an examiner. The examiner will read the incoming communication to determine the nature of the offense, the names of the suspects and victims, and the types of requested examinations. It is important to have an understanding of the offense to help determine the course of action in the Laboratory. Contact between family members or friends would be treated differently, as the transfer of trace evidence would be more likely in these cases. In the Unit, there are three processing rooms designed for debris collection. Debris is collected through a combination of picking, scraping, and sometimes taping. Whereas taping is considered by some laboratories to be a preferred technique, it can be time-consuming and tedious and can present a storage problem for the tape collections. Vacuuming is not recommended for clothing items. The clothing of a victim is processed in a room other than the room in which the suspect’s clothing is processed. The collected debris is placed in pillboxes and examined with a stereobinocular microscope. Hairs and fibers are mounted on glass microscope slides for identification and comparison purposes. |
|
Examination Conclusions
| When a questioned hair exhibits the same microscopic characteristics as the known hairs of an individual, the hair could have originated from that individual. If the questioned hair is microscopically dissimilar to the known hair standard, it cannot be associated with the individual. Different people generally have different hair characteristics, but differences in microscopic characteristics can also be the result of time and alteration. Known hair samples should be collected from individuals as soon as possible to the date of the crime. As time passes, microscopic characteristics can change, and the individual may alter the color with dyes. |
|
If a fiber exhibits the same microscopic and optical properties as a known fabric, the fiber could have originated from that fabric. Although it is not possible to say that a fiber originated from a particular fabric, fiber matches are not insignificant. Because of the many different types of fibers and fabrics and the many different ways they can be colored, the likelihood of finding coincidental matches is low. It is possible, however, to positively say that a torn piece of fabric originated from another fabric if the torn edges match.
For more information about trace evidence and the recovery of evidence from crime scenes, see the Hairs and Fibers and Crime Scene Search sections of the Handbook of Forensic Services.