Forensics Study Guide: Hair, Fibers, and Fingerprints

Flashcards reviewing forensic evidence concepts including hair analysis, fiber testing, and fingerprint patterns and processing.

When does hair evidence qualify as individual evidence versus class evidence?

Hair is individual evidence when it has a root or follicle attached containing nuclear DNA (or a catagen root yielding nuclear DNA). It is class evidence when it lacks a root or follicle and only contains mitochondrial DNA.

What is the difference between macroscopic and microscopic hair examination?

Macroscopic examination involves features seen with the naked eye, such as hair color, length, texture, and overall shape. Microscopic examination involves features requiring a microscope, such as cuticle scale types, cortex pigmentation, and medulla patterns.

What formula is used to calculate the Medullary Index (MI) of a hair strand?

$$\text{Medullary Index (MI)} = \frac{\text{Width of Medulla}}{\text{Diameter of Hair}}$$

How do the Medullary Index (MI) values differ between human hair and animal hair?

Human hair has an MI of $0.33$ or less, whereas animal hair has an MI of $0.50$ or greater.

If a hair strand measures $110\,\mu m$ wide with a medulla measuring $58\,\mu m$ wide, is it human or animal hair?

It is an animal hair because its Medullary Index is $\frac{58}{110} = 0.53$, which is greater than $0.50$.

What warning regarding microscopic hair analysis was revealed by the FBI and Innocence Project in 2015?

They revealed that over $90\%$ of cases involving microscopic hair analysis contained errors, establishing that microscopic analysis alone is insufficient for conviction without DNA testing.

How are natural and synthetic fibers categorized as evidence?

Both are class evidence. Natural fibers (from plants, animals, or minerals) are classified as biological evidence, while synthetic fibers (man-made) are classified as physical evidence.

What is the difference between direct transfer and secondary transfer of fiber evidence?

Direct transfer occurs when fibers pass directly from victim to suspect or vice versa. Secondary transfer occurs when fibers pass from a source to a suspect, who then passes them to a victim (or vice versa).

What non-destructive testing methods can be used to analyze fiber evidence?

Polarizing Light Microscopy, Infrared Spectroscopy / FTIR, and Microspectrophotometry (MSP).

According to the fiber burn analysis table, how do natural and synthetic fibers differ in flame behavior, residue, and odor?

Natural fibers burn quickly without shrinking away, leave brittle ash, and smell like burning wood or campfire. Synthetic fibers tend to melt, solidify/harden when cooled, and emit a chemical odor.

What are the three core principles of fingerprint analysis?

1. Fingerprints are unique (no two people share identical ridge characteristics). 2. Fingerprints stay unchanged (formed by the 10th week of gestation). 3. Fingerprints are systematic (classified into loops, whorls, and arches).

What percentage of the population possesses loops, whorls, and arches?

Loops: $60\%\text{--}65\%$, Whorls: $30\%\text{--}35\%$, and Arches: $5\%$.

How do Ulnar Loops and Radial Loops differ?

An Ulnar Loop opens toward the pinky finger (ulna bone side), while a Radial Loop opens toward the thumb (radius bone side).

How does a Plain Whorl differ from a Central Pocket Loop Whorl?

In a Plain Whorl, an imaginary line between the two deltas touches or crosses a central circular ridge. In a Central Pocket Loop Whorl, the imaginary line between deltas does not touch the inner circular ridges.

According to the fingerprint reference chart, what ridge patterns and ridge characteristics are classified in fingerprint analysis?

Ridge pattern categories include Arches (Plain Arch, Tented Arch), Loops (Radial Loop, Ulnar Loop), and Whorls (Plain Whorl, Central Pocket Whorl, Double Loop, Accidental). Minutiae characteristics include Core, Ending Ridge, Short Ridge, Fork or Bifurcation, Delta, Hook, Eye, Dot or Island, Crossover, Bridge, Enclosures, and Specialty.

What are the key differences between latent, patent, and plastic crime scene prints?

Latent prints are invisible prints left by body oils, sweat, and amino acids that require chemical or powder development. Patent prints are visible prints left in substances like blood, ink, or dirt. Plastic prints are 3D impressions left in soft materials like wax, clay, or putty.

How do Cyanoacrylate, Ninhydrin, Iodine Fuming, and Silver Nitrate develop latent fingerprints?

Cyanoacrylate (Super Glue) fumes react with residues to form a hard white print; Ninhydrin reacts with amino acids in sweat to turn prints purple; Iodine vapor binds temporarily to oils; Silver Nitrate reacts with salt in sweat residue.

What is the function of IAFIS and what final step is mandatory for identification?

IAFIS (Integrated Automated Fingerprint Identification System) uses algorithms to map minutiae digitally and score database samples for top potential matches. A human expert must manually perform the final verification.