Forensic Hair Analysis

What are the main areas of forensic examination of hair?

Biology (DNA), Toxicology (Drug Analysis), and Trace Evidence.

What is a key characteristic of hair in forensic science?

Hair is resistant to chemical decomposition and retains structural features over a long period of time.

What are the three layers that compose the hair shaft?

Cuticle, Cortex, and Medulla.

What is the function of the cuticle in hair?

It provides resistance and stability as the outside covering of the hair.

What are the three scale patterns of the hair cuticle?

Coronal, Spinous, and Imbricate.

How can the cuticle scale pattern be useful in forensic science?

It can aid in species identification and can be viewed under a scanning electron microscope or by making a cast of its surface.

Describe the appearance of coronal scale patterns.

Crownlike, resembling a stack of paper cups.

What is the characteristic of imbricate scale patterns?

Flattened scales with overlapping scales and narrow margins, typical of human hair.

What do spinous scale patterns look like?

Petal-like scales that are triangular in shape and protrude from the hair shaft.

What is the cortex of the hair?

The layer contained within the protective cuticle, made up of spindle-shaped cortical cells embedded with pigment granules (melanin) that give hair its color.

What is the medulla in hair structure?

A collection of cells running through the hair like a central canal.

What is the medullary index and how does it differ between humans and animals?

It measures the diameter of the medulla relative to the diameter of the hair shaft; humans have a medullary index of less than ⅓, while animals have ½ or greater.

What are the four types of medulla patterns?

Continuous, Interrupted, Fragmented, and None.

What are the three developmental stages of hair growth?

Anagen (80-90%), Catagen (10-20%), and Telogen (2%).

What occurs during the Anagen phase of hair growth?

It is the initial growth phase where the hair follicle actively produces hair, lasting up to 6 years.

What happens during the Catagen phase of hair growth?

It is a transition stage where hair continues to grow but at a decreasing rate, lasting 2-3 weeks.

What characterizes the Telogen phase of hair growth?

It is the final growth phase where hair naturally falls out, lasting 2-6 months, and roots take on a club-shaped appearance.

What factors are considered in the identification and comparison of hair?

Determining if the hair is human or animal in origin, examining scale structure, medullary index, and medullary shape.

What is necessary to determine the stage of hair growth?

A root is needed to assess the stage of growth.

What are the common areas from which hair samples are obtained for forensic analysis?

Usually from the scalp or pubic area.

What is the minimum number of full-length hairs that should be collected for analysis?

A minimum of 25 full-length hairs.

What are some techniques used for hair collection?

Picking, taping, scraping, and vacuuming.

What is the purpose of using a comparison microscope in hair analysis?

To compare the questioned and known hairs.

How can the origin of hair be determined?

It is usually easy to determine the body area from which a hair came.

What are the characteristics of scalp hairs?

Little shaft diameter variation and uniform distribution of pigment color.

What distinguishes pubic hairs from scalp hairs?

Pubic hairs are short, curly, have wide variations in shaft diameter, and a continuous medulla.

What are the characteristics of beard/mustache hairs?

Coarse, triangular in cross-section, and have a blunt tip from cutting or shaving.

What are the characteristics of eyelash/eyebrow hairs?

They are typically shorter and finer than scalp or pubic hairs.

What are the hair characteristics associated with European ancestry?

Straight or wavy, very fine to coarse pigments, pigments are more evenly distributed, and cross-section is oval to round.

What are the hair characteristics associated with Asian ancestry?

Regularly coarse, straight, thick cuticle, continuous and wide medulla, large pigment granules with a reddish appearance, and cross-section is circular.

What are the hair characteristics associated with African ancestry?

Kinky or curly, dense pigmentation that is clumped, unevenly distributed pigments, and cross-section is flat to oval.

What does the presence of dye or bleach in hair indicate in terms of sex determination?

It can indicate the sex of the individual.

How can age be determined from hair characteristics?

Only in the case of infant hair, which is fine, short in length, and has fine pigment.

What is the significance of microscopic examination of the hair root in cases of forcible removal?

It helps determine whether the hair fell out naturally or was pulled from the skin.

What does the presence of fungal or nit infections indicate in hair analysis?

It indicates potential contamination or health issues related to the individual.

What should be ensured when collecting hair samples from victims and suspects?

Samples must come from the same area of the body to ensure a representative sampling.

What is the significance of root banding in hair analysis?

Root banding is a phenomenon consistent with hair from a deceased individual's head, often observed as darkening around the root.

What are the two types of DNA found in hair analysis?

Nuclear DNA, found in the root or follicular tissue, and mitochondrial DNA, found in the cellular material outside the nucleus.

Why is nuclear DNA considered the richest source of DNA in hair?

It has a higher rate of success during the anagen phase and is more definitive for individualization.

What is a limitation of mitochondrial DNA in hair analysis?

Mitochondrial DNA cannot distinguish microscopically similar hairs from different individuals who are maternally related.

What potential for error exists in hair analysis?

The analysis is subjective and highly dependent on the skills and integrity of the analyst.

What was the Central Park Jogger case about?

In April 1989, a young woman was attacked while jogging, leading to the wrongful conviction of five boys based on hair evidence.

What evidence linked the boys to the Central Park Jogger case?

Two hairs consistent with the victim's head hair and one consistent with her pubic hair were found on one boy's clothing.

What does the NAS report say about hair evidence?

It states that hair analysis can be useful to narrow the pool of suspects but lacks scientifically accepted statistics on hair characteristics.

What is the recommended approach for microscopic hair comparisons?

They must be regarded as presumptive, and all positive comparisons should be confirmed by DNA.

What is the role of examiner proficiency in hair analysis?

The reliability of hair analysis depends heavily on the examiner's proficiency and practical experience.

What conclusions can be drawn from comparing questioned and known hair samples?

Similar microscopic characteristics can include the known hair as a possible source, while dissimilar characteristics exclude it.

What is the difference between nuclear and mitochondrial DNA in terms of quantity?

Mitochondrial DNA has many more copies in a cell compared to nuclear DNA.

What does the term 'presumptive' mean in the context of hair analysis?

It indicates that microscopic hair comparisons should not be taken as definitive proof without further confirmation.

Why is there a lack of uniform standards in hair analysis?

Until 2012, hair examiners lacked written standards defining scientifically appropriate ways to explain results in court.

What does the term 'microscopic characteristics' refer to in hair analysis?

It refers to the observable features of hair that can be compared between questioned and known samples.

What is the role of hair analysis in forensic investigations?

Hair analysis can help narrow down suspects but is not definitive without DNA confirmation.