Shards and Silts Slides SHARDS & SILTS
The Science of Trace Evidence
Forensic Unit 4: Trace Evidence
The Golden Rule
Locard's Exchange Principle
"Every contact leaves a trace."
— Dr. Edmond Locard
When two objects come into contact, there is a transfer of material.
Trace evidence is often microscopic and easy to overlook.
Dirty Details: Soil
Color
Indicates mineral content and moisture. Over 1,100 different soil colors exist!
Texture
The ratio of sand, silt, and clay. Determines how the soil "feels" and behaves.
pH Level
Acidity or alkalinity can link a suspect to a specific geographic location.
Soil sticks to shoes, tires, and clothing, making it a perfect trace evidence "tag."
Shattered Clues: Glass
Fracture Patterns
• Radial: Lines like a spiderweb
• Concentric: Circles around the hit
Physical Properties
• Density: Does it sink or float?
• Refraction: How does it bend light?
Glass Analysis
FIELD MISSION
The Outdoor Trace Scavenger Hunt
Your Goal
Locate 8 evidence stations. Analyze soil and glass properties to solve the mystery.
Field Rules
No running. Respect the property. Don't touch glass fragments without gloves.
Investigator Field Notebook Case File #2026-TRCE
FIELD INVESTIGATOR'S NOTEBOOK
Investigator Name
Date
Soil Evidence Collection
Station 01
LOCATION: GARDEN
Color & Texture Notes
Station 02
LOCATION: PATHWAY
Color & Texture Notes
Station 03
Location: Forest Edge
Color & Texture Notes
Station 04
Location: Playground
Color & Texture Notes
Use the hand lens to look for inclusions like minerals or organic matter.
Page 1
Glass Fragment Analysis
Station 05
Bench Area
Edge Description & Tint
Station 06
Parking Lot
Edge Description & Tint
Station 07
Window Ledge
Edge Description & Tint
Station 08
Recycling Bin
Edge Description & Tint
Post-Mission Analysis
1. Comparison: Which soil station was the stickiest (clay-like)? Why is this helpful for tracking a suspect's location?
2. Differentiation: How did the glass from the parking lot (Station 6) differ from the window ledge (Station 7)?
Confidential Field Document - Investigator Use Only
Evidence Station Cards Evidence Station Cards
Cut along the dashed lines. Laminate for durability. Place next to evidence samples.
Soil 01
The Garden Plot
Investigator Tip:
"Notice the dark, rich color. This indicates high organic matter (humus). Rub it between your fingers. Does it feel gritty or sticky?"
Field Unit 2026-TRCE
Soil 02
The Walking Path
Investigator Tip:
"This sample is lighter in color. Sand particles are large and visible; clay particles are too small to see. Which is dominant here?"
Field Unit 2026-TRCE
Soil 03
The Forest Edge
Investigator Tip:
"Look for inclusions. Leaf bits, moss, or specific types of small rocks like quartz that are only found in shaded forest areas."
Field Unit 2026-TRCE
Soil 04
The Playground
Investigator Tip:
"Trace evidence can be human-made. Do you see rubber mulch or fine gravel mixed in? How does this 'tag' the suspect's shoes?"
Field Unit 2026-TRCE
Glass 05
Bench Area
Investigator Tip:
"Examine the edges. These fragments are curved and thin. Is this from a beverage bottle? Note the color tint carefully."
Safety Restricted
Glass 06
Parking Lot
Investigator Tip:
"Look for 'cubed' fragments with duller edges. This is tempered safety glass. Where is this found on a vehicle?"
Safety Restricted
Glass 07
Window Ledge
Investigator Tip:
"Flat and razor sharp. This is plate glass. Look for radial fracture lines if a larger piece is present."
Safety Restricted
Glass 08
Recycling Bin
Investigator Tip:
"Look for manufacturer symbols or stamps. These can pinpoint where a product was made and narrow down a list of stores."
Safety Restricted
Caution: Investigator Safety
Do not touch glass fragments with bare hands. Use tools or examine within sealed containers only.
Trace Evidence Teacher Guide Facilitation Guide
Case: Shards & Silts Scavenger Hunt
Field Setup
• Distribute 8 cards around grounds.
• Soil: Use open petri dishes with varied samples.
• Glass: SEAL all fragments in jars/bags. NEVER leave loose glass.
Safety Rules
• No student contact with bare glass.
• Gloves mandatory for glass station prep.
• Students must walk at all times.
• All samples remain at their stations.
Investigation Key
ID Sample Type Key Features Forensic Significance 01 Garden Soil Dark brown; sticky (clay). Likely from a manicured/watered zone. 02 Path Sand Light tan; gritty; loose. Travel on high-traffic sand trails. 03 Forest Dirt Leaf litter, acidic debris. Links to unmaintained/wild area. 04 Playground Mixed with rubber bits. Highly specific human-made mix. 05 Bottle Glass Curved; amber/green tint. Discarded food/drink container. 06 Vehicle Glass Cubic; dull edges. Evidence of car collision/break-in. 07 Plate Glass Flat; sharp edges; clear. Links to building window breakage. 08 Industrial Glass Frosted or etched marks. Industrial or specific lab origin.
Case closure discussion
"Hypothetical: A suspect's boots have soil from Station 03 (Forest) and glass shards from Station 07 (Window). What sequence of events does this suggest?"
