Forensics 1: Unit 3: Trace Evidence: Hair -Encountered as physical evidence in a wide variety of crimes. -Not yet possible to individualize a human hair to a single head or body. -When properly collected at the crime scene and submission to the lab is accompanied by an adequate number of controls, hair can provide strong corroborative evidence for placing an individual at a crime site. -Hair grows out of hair follicle. Cuticle -Outside covering of hair; used as protection. -Formed by overlapping scales that always point toward the tip end of each hair. Cortex -Made up of spindal-shaped cells that are aligned parallel to the length of the hair; important since it contains the pigment granules. -Used to compare color. Video:
Human Dog Deer Rabbit Cat Horse
Cross Section Medulla -Central canal running through a hair -Medullary index-measures the diameter of the medulla relative to the diameter of the hair shaft. -Index for humans--less than 1/3 -Index of other animals--greater than 1/2 -Classification: Continuous, Interrupted, Fragmented, or Absent
Human Dog Deer Rabbit Cat Mouse
Identification and Comparison of Hair -First step is to determine if the hair at a crime scene is human or animal -Look for scale structure, medullary index, and medullary shape. -Often use a comparison microscope -Match color, length, and diameter -Considered Class Evidence Can the species of a hair be determined? Yes -The medullary index is used to determine species. -Look for size of medulla. -Look at scale pattern Can the body area of a hair be determined? Yes -Scalp--has little variation in diameter (usually an interrupted medulla) -Pubic--more diameter variation; tends to be shorter, more tightly coiled, and a continuous medulla. -Facial Hair--coarser (heavy) -triangular cross section -blunt tip as opposed to pointed tip
Identification and Comparison of Hair Cont. Can the racial origin of a hair be determined? Somewhat -Becoming more difficult due to interracial relationships -Caucasian--straight or wavy; very fine to coarse; pigments are more evenly distributed. -Negroid--containing dense, unevenly distributed pigment; kinky curly Can the age and sex of a hair be determined? Not really?? -Sex: not unless DNA is present - -?? Length (short--males); (long--females) -?? Coloring -Age: It s a challenge (can t tell) -infant hair is much finer than adults
Is it possible to determine if hair was forcibly removed from the body? Goes through growth and dormant phases -Rate of growth is fairly predictable -Hair will stay until new growth begins Yes -Look at ends of hair: -Falls out--see tip and not much else (no root) -Pulled out--the root bulb is attached--dna analysis
Identification and Comparison of Hair Cont. Are efforts being made to individualize human hair? Somewhat -Still having trouble finding morphological differences -Currently using DNA from the nucleus -Advances are being made in the use of DNA from mitochondria -There is a greater chance of finding a mitochondria than a cell nucleus -Mitochondrial DNA comes from the mother Collection of Hair Evidence -When hair is sent to a lab, it must be accompanied by an adequate number of control samples from the victim and a suspect. -Hair has a lot of variation: Scalp-50 full lengths of hair Pubic-25 full lengths of hair -Pull hair out of skin or clip at skin line -Comparison microscope is often used -Forensic analyst would say, The sample is consistent or not consistent with the suspect.
Trace Evidence: Fibers -Important in incidences that involve personal contact -Transfer--Locard s Principle -Fibers, like hair, are easily exchanged so they can provide evidence of personal contact and possible association between victim and suspect or object. Natural -Derived from animal or plant sources -Most are natural fibers Ex.) cotton-most prevalent wool-hair silk mink-hair leather Man-Made -After the industrial revolution, synthetic fibers were born. -1939--Rayon was invented -First man-made were processed from cotton -polymers -Most synthetics are made from chemicals Ex.) nylon, decron, acetate Polymers -Repeating sequence of a chemical compound -Long chain of compounds
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