Presentation on theme: "Forensics of Hair Analysis. Hair Forensics One of the most common is hair evidence. helpful in demonstrating physical contact with a suspect Until recently,"— Presentation transcript:
Forensics of Hair Analysis
Hair Forensics One of the most common is hair evidence. helpful in demonstrating physical contact with a suspect Until recently, the comparison microscope was considered the only reliable tool for the identification and comparison of the microscopic characteristics found in hair Today, nuclear and mitochondrial DNA (mtDNA) testing can provide additional information that can influence the value of microscopic examinations
Basic Hair Structure
Hair Facts A hair grows from the papilla and with the exception of that point of generation is made up of dead, cornified cells It consists of a shaft that projects above the skin, and a root that is imbedded in the skin
Hair Its basic components are keratin (a protein), melanin (a pigment), and trace quantities of metallic elements. These elements are deposited in the hair during its growth and/or absorbed by the hair from an external environment. After a period of growth, the hair remains in the follicle in a resting stage to eventually be sloughed from the body.
Hair Cuticle The cuticle is a translucent outer layer of the hair shaft consisting of scales that cover the shaft. Cuticular scales always point from the proximal or root end of the hair to the distal or tip end of the hair.
Cuticle There are three basic scale structures that make up the cuticle—coronal (crown-like), spinous (petal-like), and imbricate (flattened). Combinations and variations of these types are possible.
Bat Hair and Mink Hair
Human Hair The imbricate or flattened scales type consists of overlapping scales with narrow margins. They are commonly found in human hairs and many animal hairs.
Medulla The medulla is a central core of cells that may be present in the hair. Human Animal Deer
Medulla The medulla, when present in human hairs, is generally less than one-third the overall diameter of the hair shaft. The medulla in animal hairs is normally continuous and structured and generally occupies an area of greater than one-third the overall diameter of the hair shaft. There are many more characteristics of hair that are too numerous to discuss for the purpose of this lab
Animal Versus Human Hairs Human hairs are generally consistent in color and pigmentation throughout the length of the hair shaft, whereas animal hairs may exhibit radical color changes in a short distance, called banding. The pigmentation of human hairs is evenly distributed, or slightly more dense toward the cuticle, whereas the pigmentation of animal hairs is more centrally distributed, although more dense toward the medulla.
Hair Forensics Hairs found on a knife or club may support a murder and/or assault weapon claim. A questioned hair specimen can be compared microscopically with hairs from a known individual, side-by-side. Human hairs can be classified by racial origin such as Caucasian (European origin), African-American (African origin), and Mongoloid (Asian origin). In some instances, the racial characteristics exhibited are not clearly defined, indicating the hair may be of mixed-racial origin.
Hair Forensics The region of the body where a hair originated can be determined with considerable accuracy by its gross appearance and microscopic characteristics. The length and color can be determined. It can also be determined whether the hair was forcibly removed, damaged by burning or crushing, or artificially treated by dyeing or bleaching.
Hair Forensics: DNA Often it is not possible to extract DNA fully, or there is not enough tissue present to conduct an examination. Hairs with large roots and tissue are promising sources of nuclear DNA. However, DNA examinations destroy hairs, eliminating the possibility of further microscopic examination.
Hair Forensics: Collection Hairs can be recovered from items using a number of different techniques. Some of the methods used to collect hairs from clothing and bedding items are scraping, shaking, taping, and picking. Debris from large carpeted surfaces might be vacuumed into a filtered canister. If the specific location of a hair on a clothing item is important, it might be necessary to pick off the hair or tape the item and record where the hair was removed.
Hair Forensics: Which Hairs? Head hairs and pubic hairs exhibit a greater range of microscopic characteristics than other human hairs; therefore, head and pubic hairs are routinely forensically compared. Twenty-five randomly selected head hairs are generally considered adequate to represent the range of hair characteristics of that individual. It is recommended that the same number of hairs be collected from the pubic region.
Forensic Identification Human hairs can generally be identified by racial origin, body area, and other comparison characteristics. Racial indicators apply primarily to head hairs.
Caucasian African- American Mongoloid
Where is this hair from? Certain features of individual hairs identify the region of the body where it originated. Pubic Hair
Where is this Hair from? Limb
Where is this hair from? Beard
There are also certain characteristics for Underarm hair Chest hair Eyebrow General body hair
Things to consider when viewing hair Length: Length is considered, although hairs may have been cut between the time of deposition of the questioned specimen and the collection of a known sample. In addition, there may be a significant difference in the lengths of the shortest and longest hairs on an individual's head. Tip: The tip can be cut, broken, split, abraded (rounded), or finely pointed as illustrated by An individual's grooming, hygiene, health, and nutrition can affect these features.
Glass- Cut or Broken Hair Tip Cut Hair Tip Worn Razor-Cut Tip
Dyed hairs possess an unnatural cast or color. In addition, the cuticle will take on the color of the dye