Forensic Hair Analysis Hair and Crime o Locards

  • Slides: 29
Download presentation
Forensic Hair Analysis

Forensic Hair Analysis

Hair and Crime o Locard’s Exchange Principle o Most common type of Trace Evidence:

Hair and Crime o Locard’s Exchange Principle o Most common type of Trace Evidence: materials that are generally small in size and can be easily transferred when physical contact occurs between people and/or objects o Scenarios involving hair evidence: homicide, sexual assault, aggravated assault, hit-and-run incidents

Hair Evidence o Composed of mostly protein keratin o Outgrowths of skin of mammals

Hair Evidence o Composed of mostly protein keratin o Outgrowths of skin of mammals o Each species has characteristic hair n Length, color, shape, root appearance, hair anatomy o Variability also exists from body part to body part n Head, arms, legs, pubic, armpits, face

What makes hair good evidence? o Resistance to chemical decompostition o Ability to retain

What makes hair good evidence? o Resistance to chemical decompostition o Ability to retain structural features over long period of time o Can get DNA from root

Hair Microscopy o o o o Used to determine human vs. animal Specify race

Hair Microscopy o o o o Used to determine human vs. animal Specify race Part of body Fell out naturally? Removed by force? Person on drugs? Have disease? Specify if hair was dyed Cut with scissors, razor, or burned

Hair Characteristics

Hair Characteristics

Hair Characteristics

Hair Characteristics

Parts of a Hair o Cuticle o Cortex o Medulla

Parts of a Hair o Cuticle o Cortex o Medulla

The Cuticle o Formed by overlapping scales n Always point to the tip end

The Cuticle o Formed by overlapping scales n Always point to the tip end of each hair n Scales form from keratinized, flat cells that come from follicle o Scale pattern cannot individualize human hair n Used for species determination n Use nail polish casting to see scale pattern

Pics of the cuticle o Coronal scales o Found in small rodents, bats o

Pics of the cuticle o Coronal scales o Found in small rodents, bats o Rarely in humans

More on the cuticle o Spinous scales o Found in mink, seals, cats

More on the cuticle o Spinous scales o Found in mink, seals, cats

Human cuticle pattern o Imbricated or flattened o Found on humans and many animals

Human cuticle pattern o Imbricated or flattened o Found on humans and many animals

Medulla o o Core of hair Not always present or present in only parts

Medulla o o Core of hair Not always present or present in only parts Medulla of human hair varies Also depends on body region n n Head – often missing or narrow pubic – often wide & continuous Limb – discontinuous & granular Beard – double medullas o Animals have specific pattern

Common medulla shapes o In humans, you will usually see… n n Absent Trace

Common medulla shapes o In humans, you will usually see… n n Absent Trace (fragmented) Discontinuous (interrupted) Continuous

Human Medullas

Human Medullas

Medulla - animal o Uniserial ladder medulla – rabbit o Multiserial ladder medulla -

Medulla - animal o Uniserial ladder medulla – rabbit o Multiserial ladder medulla - rabbit

Medulla - animal o Lattice – deer o Thick, continuous = dog

Medulla - animal o Lattice – deer o Thick, continuous = dog

Other animal medulla o Cat – o Seal -

Other animal medulla o Cat – o Seal -

Cortex o Main body of hair o Contains pigment granules n Mostly found in

Cortex o Main body of hair o Contains pigment granules n Mostly found in root, but may be founds throughout length of human hair o Determine color o Also use thickness to determine match

Root and Hair Growth o 3 Developmental Stages n Anagen n Catagen n Telogen

Root and Hair Growth o 3 Developmental Stages n Anagen n Catagen n Telogen

Anagen Growth o Initial growth stage in which the hair follicle actively produces hair

Anagen Growth o Initial growth stage in which the hair follicle actively produces hair o Longest – can last between 2 -6 years o Hair grows and dead, keratinized cells are pushed through the scalp o Root is attached to follicle

Catagen o Transitional Phase n 1 -2 weeks o Hair stops growing o Root

Catagen o Transitional Phase n 1 -2 weeks o Hair stops growing o Root has club-like appearance

Telogen o Lasts approximately 3 months o Once follicle stops producing keratin, hair naturally

Telogen o Lasts approximately 3 months o Once follicle stops producing keratin, hair naturally sheds o At any one time, about 10 -18% of head hairs are in the telogen o Follicle is hard, white lump

Animal vs. Human hairs o Human hair – consistent color, animal can change radically

Animal vs. Human hairs o Human hair – consistent color, animal can change radically across hair o Medulla occupies much larger space (> 1/3 diameter) in animals o Scale patterns o Wide variability among animal hairs n n n Coarse outer hairs (guard hairs) Fine fur hairs Tactile hairs (whiskers) Tail hairs Mane hairs

Collecting Hair Evidence: 6 Main Methods o Observable hairs collected with tweezers n However,

Collecting Hair Evidence: 6 Main Methods o Observable hairs collected with tweezers n However, tweezers can damage hair structure or break root where DNA exists n Infrared or laser sources can make hairs more visible o Clear tape lifts visible and nonvisible hairs off a variety of surfaces n Each piece of tape labeled for source

More ways to collect hair o For larger crime scenes, vacuuming may be used

More ways to collect hair o For larger crime scenes, vacuuming may be used n Also good for stationary objects that cannot be transported o Brushing, scraping, or shaking garment over large sheet of white paper o Garment bagged and agitated o Combing – used to detect cross transfer of hairs

FAQ 1: Can age/sex of an individual be determined by a hair? o Age

FAQ 1: Can age/sex of an individual be determined by a hair? o Age cannot be determined except with infant hair (very fine) o Sometimes dye/bleaching offers a guess to sex o Nuclear DNA will tell male/female

FAQ 2: Can you tell if the hair was forcibly removed? o Hair root

FAQ 2: Can you tell if the hair was forcibly removed? o Hair root w/ follicular tissue (root sheath cells) adhering to it n Pulling or forcibly combing/brushing o Hair naturally falling off has bulbousshaped root free of tissue

FAQ 3: How can you individualize human hair? o Look at the nuclear DNA

FAQ 3: How can you individualize human hair? o Look at the nuclear DNA in hair root or on surrounding tissue (preferable) o When no follicular tissue present, mitochondrial DNA (passed from only mother to child) from root cells n Much more available than nuclear o Nucl. DNA can narrow to 1 in one billion; mitochondrial cannot individ.