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Crime, and Evidence |
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Trace Evidence Unit Federal Bureau of Investigation Washington, DC |
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Introduction |
Crime Scene Search |
Evidence Collection |
Evidence Handling Procedures |
Protocol for Evidence Processing |
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.
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:
The following are suggestions for collecting evidence from crime scenes such as houses, apartments, and vehicles:
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 headbandsthe 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. |
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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. |
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 bagsnot 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.
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. |
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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. |
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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.
FORENSIC SCIENCE COMMUNICATIONS JULY 2000 VOLUME 2 NUMBER 3
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