Unit 3 Hair as Evidence A. Hair as evidence a. Human hair is one of the most frequently pieces of evidence at the scene of a violent crime. Unfortunately, hair is not the best type of physical evidence for establishing. It is not possible to show with any certainty that two hairs came from the same person or animal. However, hair can be used to certain suspects or scenarios. It can also be used to (support) other physical evidence if it is consistent with the rest of the evidence. b. The average human has approximately 250,000 hairs that get replaced in a cycle. i. About hairs are shed daily; about being from the head. ii. tend to have more head hairs then brunettes. have the least. c. Hair is considered evidence. Alone (without follicle cells attached), it cannot be used to identify a specific individual. d. In the best case, an investigator can identify a group or class of people who share similar traits who might share a certain type of hair. e. Hair can easily be left behind at a crime scene. It can also adhere to clothes, carpets, and many other surfaces and be transferred to other locations. This is called. Secondary transfer is particularly common with hair. f. Because of its tough outer coating, hair does not easily. g. Hair analysis may be helpful to determine the following: i. Human or animal ii. the broad background of an individual iii. from which the hair came iv. manner in which the hair was v. Chemical tests can provide a history of the use of and other toxins, indicate the presence of, and provide an assessment of nutritional. vi. When the follicle of a hair is present, evidence may be obtained and it can lead to individual identification. h. Collecting hair as evidence i. Recover all hair present. ii. Use or to pick up visible strands of hair when possible. may be used to help collect hairs if needed. When surfaces are large, they can also be. iii. Place hair in paper or envelopes which should then be folded and sealed in larger envelopes. Label the outer sealed envelope. iv. If hair is attached, such as in dry blood, or caught in metal or a crack of glass, do not attempt to remove it but rather leave hair on the object. If the object is small, mark it, wrap it, and seal it in an envelope. If the object is large, wrap the area containing the hair in paper to prevent loss of hairs during shipment. Unit 3 Hair as Evidence 1
B. Function of Hair a. All mammals have hair. Its main purpose is to body temperature to keep the body warm by insulating it. b. Other functions of hair: i. decrease ii. to protect against iii. c. In many mammals, hair can be very dense, and it is then referred to as. d. In humans, body hair is mostly ; it does not play as large a role in temperature regulation as it does in other animals. When humans are born, they have about hair follicles, only percent of which are on the head. This is the largest number of hair follicles a human will ever have. As a human ages, the density of hair. C. Structure of Hair a. All hair has the same basic structure. b. A hair consists of two parts: a and a. i. Follicle is a -shaped structure in the 1. Hair is produced from the follicle. Humans develop hair follicles during fetal development, and no new follicles are produced after birth. 2. At the end of the follicle is the, a network of blood vessels that supply to feed the hair and help it. 3. The bulb also contains a sebaceous to secrete oil, erector that cause hair to stand upright, and cells to respond to the environment. ii. The hair shaft is composed of the protein, which is produced in the skin. Keratin makes hair both strong and. 1. The hair shaft is made up of three layers: a. Cuticle- outer layer of the hair; the hair. i. made of that overlap one another and point toward the tip end b. Cortex middle layer; largest part of the hair shaft, contains granules i. There are two main pigments found in human hair: 1. Eumelanin- gives color to or hair 2. Pheomelanin- produces the color in or hair ii. Small sacs of air called are also found in this region, especially closer to the root, and tend of be different shapes and sizes. Unit 3 Hair as Evidence 2
iii. The cortex provides hair with strength, elasticity and determines the texture and quality of hair. c. Medulla- Central core of the hair. It can be a tube, or filled with. i. Forensic investigators classify hair into different groups depending on the appearance of the medulla. ii. Human hairs generally have medulla or one that is fragmented, however a continuous medulla is frequently found in the hairs of Americans and Asians. iii. hairs show a wide variety of medulla patterns. 2. A good analogy for the structure of a hair shaft is the structure of a pencil a. being the lead b. being the wood c. being the paint Good example of a microscope drawing of hair: (however you should use colored pencil) D. Differences in Hair a. Hair can vary in shape, length, diameter, texture, and color. b. The of the hair may be circular, triangular, irregular, or flattened, influencing the curl of the hair. c. The of hair can be coarse as it is in whiskers or fine as it is in younger children. d. Some furs are a mixture as in dog coats, which often have two : one fine and one coarse. Unit 3 Hair as Evidence 3
e. Hair color varies depending on the distribution of pigment granules and on hair dyes that might have been used. f. Differences in hair can be used for identification or in forensic investigations Hairs could have a common origin Hairs do not have a common origin g. In humans, hair varies from person to person. h. Different hairs from one location on a person can vary. i. Not all hairs on someone s head are exactly the same. i. Example- a suspect may have a few gray hairs among brown hairs in a sample taken from his head. j. Because occur within each body region, hairs are usually collected from a suspect s head. Typically, hairs are collected from the pubic region. i. The recommended method for collecting head hairs is to start by having the person from whom they are being collected bend over a large sheet of clean paper, rubbing or massaging their hands through the hair so that hair will on the paper. More should then be gathered by them from representative areas all over the head. A total of 50-100 hairs are desired. Do not the hair. E. Hair from Different Parts of the Body a. Hair varies from region to region on the body of the same person. b. Forensic scientists distinguish six types of hair on the human body: i. hair ii. and iii. and mustache hair iv. hair v. Auxiliary or hair vi. hair c. Each hair type has its own shape and characteristics. Female vs. Male d. Hair from head and pubic region are the most hairs found at crime scenes. e. Hair from other animals are also frequently found (pets, farm animals, fur from clothing) F. The Life Cycle of Hair a. Hair goes through several stages during its life. i. stage 1. Period of active when the cells around the follicle are rapidly dividing and depositing materials 2. Lasts approximately 1,000 days; Approx. % of all human hair is in this stage ii. stage 1. Transitional or stage that lasts a few weeks; hair growth slows. 2. Accounts for about % of all hair growth and development iii. stage 1. During this final stage, the hair follicle is dormant and hairs are easily. Body Hair Unit 3 Hair as Evidence 4
2. About % of all hairs are in this stage. Lasts a few months. b. Distal Tips i. The appearance of the tip of the hair shaft is an important characteristic. ii. If sufficient sample is available, it may be possible to identify the type of treatment and estimate the length of time since the last cutting. Uncut Scissors (freshly cut) Razor Clippers Draw distal tip hair shapes here Tip is tapered, round, split, or frayed. Tip is partially compressed. Tip has a long tail on one side of the cut. iii. Tips usually take on a rounded form in 2-3. Reveals broken and partially cut shafts. G. Treated Hair a. When a person chemically treats his or her hair, traces of the chemicals used. Some of these changes are subtle and can be detected only by using a. b. Bleaching hair removes pigment granules and gives hair a tint. It also makes hair and can disturb the scales on the cuticle. c. Artificial bleaching shows a demarcation along the hair, while bleaching from the sun leaves a more mark. d. Dyeing hair changes the color of the hair shaft. An experienced forensic examiner can immediately recognize the color as unnatural. In addition, the cuticle and cortex both take on the color of the dye. e. If an entire hair is recovered in an investigation, it is possible to when the hair was last color-treated. The region near the root of the hair will be colored naturally. f. Human hair grows at a rate of about per month (approximately 0.44 mm per day). Measuring the length of hair that is naturally colored and dividing by 1.3 cm provides an estimate of the number of months since the hair was colored. H. Racial Differences a. Broad racial categorization can be made by identifying certain characteristics of hair. Unit 3 Hair as Evidence 5
I. Animal Hair and Human Hair a. Human hair differs from that of other animals. b. One of the more reliable ways to distinguish between a human and other animal hair is to calculate the medullary index of the hair. i. Diameter of the by the diameter of the entire hair is known as the medullary index. If the medullary index is 0.5 or greater, the hair came from an. If the medullary index is 0.33 or less, the hair is from a. * MATH * medullary index = diameter of medulla diameter of entire hair c. Characteristics of the cuticle may be important in distinguishing between hairs of different species. i. Cuticle scales differ between species of animals; three basic scale structures include: coronal (crown-like) Imbricate (flattened) Spinous (petal-like) Found in hairs of very fine diameter and resemble a stack of paper cups Coronal scales are commonly found in the hairs of small and bats but rarely in human hairs Overlapping scales with narrow margins They are commonly found in human hairs and many animal hairs Triangular in shape and protrude from the hair shaft Found on the fur hairs of mink, seals,, and some other animals. They are never found in human hairs Unit 3 Hair as Evidence 6
J. Microscopy a. Hair viewed for forensic investigations is studied both macroscopically and microscopically. i.,, and curliness are macroscopic characteristics. ii. Microscopic characteristics include the pattern of the medulla, pigmentation of the cortex, and types of scales on the cuticle. b. Different kinds of microscopes provide different kinds of evidence. i. microscopes are especially important tools to the forensic investigation of hair. ii. A microscope is equipped with filters to detect fluoresced light, indicating the presence of a dye or other treatment. iii. microscopes provide incredible detail of the surface or interior of the sample, magnifying the object 50,000 times or more. K. Testing for Substances in the Hair Shaft a. Because hair grows out of the, chemicals that the skin and some toxins and drugs which an individual can leave in the hair. b. In order to test hair, it must first be in an organic solvent that breaks down the and releases any substances that have been incorporated into the hair. A forensic chemist can then perform chemical tests for the presence of various substances to provide evidence of or drug use. c. Investigators can calculate the length of time during which a person was taking drugs or ingesting other toxins by testing different parts of the hair. d. activation analysis (NAA) is another useful technique that can identify up to 14 different in a single two-centimeter-long strand of human hair. The probability of the hairs of two individuals having the same concentration of these different elements is about one in a million. L. Testing the Hair Follicle a. If hair is forcibly removed from a victim or suspect, the entire hair follicle (called a ) may be present. If so, and attached to the follicle may be analyzed for blood type and. b. DNA analysis of the hair follicle provides with a high degree of confidence, whereas analysis of the hair shaft usually provides evidence only. Unit 3 Hair as Evidence 7