Forensic Science Presentation developed by T. Trimpe

Fiber Evidence A fiber is the smallest unit of a textile material that has a length many times greater than its diameter. A fiber can be spun with other fibers to form a yarn that can be woven or knitted to form a fabric. The type and length of fiber used, the type of spinning method, and the type of fabric construction all affect the transfer of fibers and the significance of fiber associations. This becomes very important when there is a possibility of fiber transfer between a suspect and a victim during the commission of a crime. Matching unique fibers on the clothing of a victim to fibers on a suspect’s clothing can be very helpful to an investigation, whereas the matching of common fibers such as white cotton or blue denim fibers would be less helpful. The discovery of cross transfers and multiple fiber transfers between the suspect's clothing and the victim's clothing dramatically increases the likelihood that these two individuals had physical contact.

Fiber Evidence Fibers are gathered at a crime scene with tweezers, tape, or a vacuum. They generally come from clothing, drapery, wigs, carpeting, furniture, and blankets. For analysis, they are first determined to be natural, manufactured, or a mix of both.

Many different natural fibers that come from plants and animals are used in the production of fabric. Cotton fibers are the plant fibers most commonly used in textile materials The animal fiber most frequently used in the production of textile materials is wool, and the most common wool fibers originate from sheep. Natural Fibers

Images: More than half of all fibers used in the production of textile materials are synthetic or man-made. Nylon, rayon, and polyester are all examples of synthetic fibers. Cross-section of a man-made fiber Synthetic Fibers Fibers under a microscope

Forensics of Fiber Analysis Cross transfers of fiber often occur in cases in which there is person-to-person contact Investigators hope that fiber traceable back to the offender can be found at the crime scene, as well as vice versa. Success in solving crimes often hinge on the ability to narrow the sources for the type of fiber found, as the prosecution did with their probability theory on the fibers

Types of Fibers - Key Acrylic YarnCotton YarnNylon Rope Polyester YarnRayon RopeWool Yarn

Lab – Part 1 Observe different samples under the microscope. –This will provide you a baseline for later in the lab when you have to identify a sample from evidence.

Hair Samples You will have 2 hair samples –Use the slides – there are only two, so share with each other. –You can use the highest magnification on these slides. –Make a sketch of each sample

Fiber Samples You will have 5 fiber samples –You only need one strand of fiber Use tweezers to remove your strand Place it on a slide – try not to use a second slide as a cover –The thickness is preventing us from using the highest power of magnification. Observe each fiber, make a sketch and record unique characteristics.

Blood Samples You will have 2 blood samples –1 human and 1 frog Look at each under the microscope –Make a sketch and record unique characteristics. There are also slides for male and female chromosomes –Look at these under the microscope, again make a sketch and record unique characteristics.

Lab – Part 2 You will be given evidence from a case. Your task is to identify the evidence by comparing it to the samples from Part 1.