FORENSIC SCIENCE Trace Evidence - Deer Valley Unified School District

[Pages:24]FORENSIC SCIENCE Trace Evidence

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Introduction

Trace Evidence--any small pieces of material, man-made or naturally occurring.

Trace evidence (in the absence of DNA) is considered class evidence. As early as the 1879, Dr. Rudolph Virchow realized that hair could only be used to eliminate suspects, but was not likely to conclusively link anyone to a crime. "The appearance of the victim's hair is not inconsistent with having come from the accused."

Remember me?

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Trace evidence: Class evidence

Most common examples:

Hair Fiber

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Hair

Human hair is one of the most frequently found pieces of evidence at the scene of a violent crime. It can provide a link between the criminal and the act (Locard's Principle).

From hair one can determine:

Human or animal

Race

Origin

Manner in which hair was removed

Treated hair

Drugs ingested

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DNA

The hair shaft contains abundant mitochondrial DNA or mtDNA--inherited only from our mothers. It can be typed by comparing relatives when nuclear DNA is not available.

It is commonly thought that only the root contains nuclear DNA. However, in rare instances, some nucleated cells called corneocytes can also be extracted from the normally degraded hair shaft.

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Hair Morphology

The Study of Structure and Form

Parts of the hair

Shaft--part of the hair that sticks out of the skin

Root--lies below the epidermis

Follicle--structure from which the hair grows

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Hair Growth

Terminology

Anagen--hair that is growing Catagen--hair at rest Telogen--hair that is dying

Length--00.5 mm per day or 1 centimeter per month; approximately one half inch per month

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Hair Cuticle

The cuticle is the outermost layer of hair which is covered with scales. Scales also always point toward the tip of the hair.

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