The Forensic Analysis of Trace Evidence

This week students were introduced to the forensic analysis of trace evidence. Students had the opportunity to make microscopic examinations of hair, fiber, and miscellaneous trace materials in an attempt to show the tremendous amount of variation present between species, manufacturer, and material.

For hair analysis, the students were to document the commonly found characteristics of hair which make identification possible. These include the cuticle, cortex, and medula. Each species varies from another in one or all of these areas enough so that identification to a species is possible. While most times microscopic hair analysis is not individualistic enough to identify one specific person, it is sufficient to eliminate persons and species from consideration. Therefore, while not conclusively identifying, it is exclusionary which is of forensic significance.

Fiber analysis is similar to hair analysis with regards to the manner in which it is performed. However, fibers do not have the same characteristics present as hair. Instead, an examiner will look at the fiber's color, crimp, luster, etc. An examiner is typically trying to differentiate between a natural fiber (those manufactured from products found in nature, such as silk, hemp, cotton, and wool), or manufactured/synthetic fibers (such as dacron, nylon, polyester, and spandex). A polarizing light microscope (PLM) is of great use in this analysis due to its ability to isolate various segments within the visible light spectrum and document the manner in which the fiber fluoresces.

Lastly, the students observed the characteristics of various items of trace evidence which are commonly found within crime scenes. These included: common household dust, pollen, drywall dust, sawdust, cosmetics, environmental pollution, charcoal, and salt crystals.

This lab helped students gain an appreciation for the difficulty of and tenacity needed to perform microscopical analysis of forensic evidence. While familiarizing them with various types of microscopes, it also aided them in gaining better insight into the world around them.

Tune in next week for our final lab of the semester... Forensic Ballistic Identification!