Hairs and Fibers Study Notes

Webextras and Key Terms

  • Anagen Phase: The initial growth phase of hair where it actively grows for up to six years, with the root potentially having a follicular tag useful for DNA analysis.

  • Catagen Phase: A transitional stage of hair growth that lasts two to three weeks where hair growth slows and the root elongates.

  • Cortex: The middle layer of hair containing spindle-shaped cells and pigment granules that determine hair color.

  • Cuticle: The outer layer of hair composed of overlapping scales that point toward the tip end, contributing to the hair's resilience.

  • Follicular Tag: A piece of tissue that may be found on the root of anagen phase hair that is crucial for DNA analysis.

  • Macromolecule: A large molecule composed of many smaller subunits, relevant in the analysis of fibers and hair.

  • Manufactured Fibers: Fibers created through chemical processes (e.g., polyester and nylon), distinct from natural fibers.

  • Medulla: The central cellular column of hair, which can vary in presence and appearance among individuals.

  • Mitochondrial DNA: DNA present in the mitochondria of cells, used in forensic investigations to establish maternal lineage.

  • Molecule: A group of atoms bonded together, representing the smallest fundamental unit of a chemical compound.

  • Monomer: The smallest unit of a polymer that can join together to form a larger molecule.

  • Natural Fibers: Fibers sourced from plants (e.g., cotton) and animals (e.g., wool), used in textiles.

  • Nuclear DNA: DNA contained within the nucleus of cells, providing a robust connection to individuals in forensic analysis.

  • Polymer: A substance composed of large molecules formed by repeating structural units, important in the composition of manufactured fibers.

  • Telogen Phase: The final stage of hair growth lasting two to six months where hair naturally falls out, presenting a club-shaped root.

Learning Objectives

After studying this chapter, you should be able to:

  • 11.1 Discuss the morphology of hair, including the three phases of hair growth

  • 11.2 Discuss the considerations and questions concerning forensic hair examinations

  • 11.3 Describe the proper collection and preservation of forensic hair evidence

  • 11.4 Identify the different types of fibers

  • 11.5 List the properties of fibers that are most useful for forensic comparisons

  • 11.6 Describe the proper collection and preservation of forensic fiber evidence

Case Study: Caylee Anthony

On July 15, 2008, Caylee Anthony was reported missing. Her grandmother, Cindy Anthony, stated she had not seen Caylee for 31 days. On retrieving her daughter Casey’s car from impound, Cindy noticed a foul odor suggesting decay. Police involvement followed, revealing discrepancies in Casey's statements regarding Caylee's disappearance. Casey was arrested for providing false statements, child neglect, and obstruction of a criminal investigation.
On December 11, 2008, Caylee's body was discovered in a wooded area close to the Anthony family home. The investigation shifted to a murder inquiry, examining Casey's car for evidence, where a single hair was found that was microscopically similar to Caylee’s. Through mitochondrial DNA analysis, similarities were established between the trunk hair and those of Caylee and Casey—consistent with maternal inheritance. An FBI analyst testified about the presence of root banding, indicating the hair likely belonged to a deceased individual. This further pointed to Caylee's temporal presence in the trunk of Casey's car, suggesting Casey's knowledge of the circumstances surrounding her daughter's death.

Introduction to Hairs and Fibers

Trace evidence, such as hair and fibers, often corroborates other investigative evidence. Although physical evidence alone does not definitively identify a suspect, it can help narrow the suspect pool. The examination of hair is particularly relevant in various crime scenarios; however, human hair cannot be individualized to a specific head or body solely by morphology. Advances in DNA analysis have provided partial success in identifying individuals through hair. The significance of hair as evidence stems from its ability to denote physical contact between suspect and victim, which is often crucial in serious crime scenarios.

The Morphology of Hair

Hair, as an appendage of the skin, grows from the hair follicle. Each hair extends from its root or bulb in the follicle, through the shaft, and ends at the tip. The hair shaft consists of three layers:

  • Cuticle

  • Cortex

  • Medulla

Cuticle

The cuticle is the outer layer covering the hair, consisting of overlapping scales that always point toward the tip end. The cuticle's structure contributes to hair's resistance to chemical decomposition and its structural retention over time. Three primary patterns describe cuticular appearances:

  • Coronal

  • Spinous

  • Imbricate

While animal hair shows varied scale patterns useful for species identification, human hair does not have unique cuticle patterns for individualization.

Cortex

The cortex, located beneath the cuticle, contains spindle-shaped cortical cells aligned parallel to the hair's length. It holds pigment granules responsible for hair color, with variations in granule composition (color, shape, distribution) serving as essential identifiers in forensic analysis. The structural features of the cortex are best examined microscopically using liquids with similar refractive indices to minimize light interference.

Medulla

The medulla is a cellular column that runs through the center of the hair, with variations in presence and appearance noted among individuals. Medullae can be classified based on their continuity and pattern:

  • Continuous

  • Interrupted

  • Fragmented

  • Absent

Human head hairs typically display either no medulla or fragmented ones, with rare continuous medullation exceptions observed in individuals of the Mongoloid race. The shape of the medulla in humans tends to be cylindrical, contrasting with varied shapes found in animals.

Hair Growth Phases

Human hair grows in three distinct phases:

  • Anagen phase: The initial growth phase allows hair to grow actively for up to six years. The root may have a follicular tag crucial for DNA analysis.

  • Catagen phase: A transitional stage that lasts two to three weeks where hair growth slows and the root elongates.

  • Telogen phase: The final phase lasting two to six months where hair naturally falls out, presenting a club-shaped root.

Identification and Comparison of Hair

The primary goal of hair examination in a forensic setting is to determine whether hair is human or animal and to match human hair from a crime scene with a suspect's hair. While animal hair comparisons are generally straightforward, human hair comparisons require meticulous attention due to inherent morphological variability.

Stable Isotope Analysis

Stable isotope analysis can provide evidence related to a victim's geographical presence based on local water consumption habits that influence hair composition. A person's movement across regions affects hair growth, providing a timeline of past locations. This analysis has proven critical in solving cases where victims were unidentified.

Considerations in Hair Examination

Examining hair involves identifying morphological features that distinguish animal from human hair, as well as enabling species identification. Scale structure, medullary index, and shape are paramount. Standard/reference samples are essential for effective examination.

  • Microscopic comparisons assess color, length, diameter, and deviations from typical hair characteristics. Known hair samples should match the specified features of questioned hairs closely.

  • Hair evidence aids in supporting prosecution claims, evident in cases like the Central Park Jogger case where microscopic hair comparisons linked suspects to the crime, despite subsequent DNA analysis revealing inaccuracies.

DNA and Hair Evidence

The introduction of DNA analysis revolutionized hair evidence examination approaches, emphasizing the need for microscopic comparisons to be supported by molecular techniques. Nuclear DNA present in hair roots provides a robust connection to individuals, with high success rates particularly associated with anagen-phase hairs. Mitigating factors include the limitation posed by telogen-phase hairs, and the assurance of using follicular tags for obtaining DNA samples is vital.

Collection and Preservation of Hair Evidence

Proper collection necessitates the juxtaposition of questioned hairs with standard/reference samples from the victim and potential suspects. Careful sampling from diverse regions of the body ensures representative sampling. A minimum of 25 full-length hairs is recommended from both scalp and pubic regions. Comb collections from victims must be handled separately to prevent contamination. Legal complications may arise if evidence is mishandled.

Forensic Examination of Fibers

Fibers may also serve as crucial trace evidence in crimes involving personal contact. The recovery of fibers allows forensic analysts to trace origins, leading to potential links between suspects and victims. Mass production complicates individual fiber identification, signaling the necessity for careful evidence analysis.

Types of Fibers

Fibers are classified broadly as either natural or manufactured:

  • Natural fibers: Sourced from plants (like cotton) and animals (like wool and silk).

  • Manufactured fibers: Created through chemical processes, including common types like polyester and nylon.

Significance of Fiber Evidence in Trials

The importance of fiber evidence is underscored in trials, where it has been instrumental in establishing connections between suspects and victims. The Wayne Williams case exemplifies fiber evidence’s role in securing convictions through demonstrable links to victim environments. Multiple fiber types serve to strengthen associations, thereby increasing the weight of evidence.

Conclusion

Hair and fiber evidence holds significant weight in forensic investigations. They require a thoughtful approach to analysis and collection, underpinning the necessity for the integration of traditional microscopy with advanced DNA analysis methods for establishing robust forensic claims.