Forensic Trace Evidence

Trace Evidence

very small pieces of material (often microscopic) that can link people, objects, and places

Transference

the process of something being picked up or left behind during contact

Objects Left at the Crime Scene

• Left-behind Items

Objects that criminals accidentally leave behind, such as clothing, paper, tools, food, or hair.

• Trace Collection

Collecting tiny evidence from items using vacuuming or careful searching.

• Physical Fit Evidence

Broken or damaged items that can be physically matched back to a larger object.
Examples:

• Broken knife tip matching the knife

• Broken car bumper pieces matching a vehicle

• Paper torn from a notebook matching a ransom note

Sources of Trace Evidence

• clothing

• footwear

• gunshot residue (GSR)

M-VAC

a vaccum-like tool that collects DNA from surfaces

Alternating Light Source (ALS)

special light used to make hidden evidence visible

Crimescope

a common ALS tool used to spot trace evidence on surfaces

Laser Scanner/ FARO 3D Scanner

a tool that scans a crime scene to create detailed 3D models and detect tiny evidence 

Video Spectral Comparator (VSC)

A device that uses different light wavelengths to reveal:

• Hidden writing

• Erased or altered text

• Ink differences

Multispectral Imaging

uses many types of lights to reveal hidden details

Nanotechnology/ Carbon Dot Powders

advanced powders used to find fibres, gunshot residue, bodily fluids, and drugs with high accuracy

Identification and Comparison

• Identification

Figuring out what a substance is by testing its physical and chemical properties.

• Class Characteristics

Shared features that place evidence into a group, not a single source.
Example: a fibre that belongs to a certain type of fabric.

• Testing Procedures

Lab tests are used to identify materials.

• Standard Materials

Known samples are used to compare against unknown evidence.

Comparison Analysis

• Comparison Analysis

Testing a suspect sample and a known sample to see if they came from the same source.

• Standard / Reference Specimen

A known sample collected from a person or object for comparison.

Two-Step Procedure

1. Choose important features from both samples.

2. Compare them to conclude whether they match.