Trace Evidence Recognition, Collection, & Preservation

Trace Evidence class w/ Dr. Elizabeth Chesna

The term for any evidence occurring in small sizes, often invisible to the human eye.

Trace evidence

Locard’s Exchange Principle

The principle that states when two surfaces make contact, material from one surface is transferred to the other surface and visa versa.

Two-way transfer

What type of transfer is a car collision?

Primary transfer

Occurs when trace evidence from the source is deposited directly to another surface.

Secondary transfer

Occurs when previously transferred trace evidence is transferred to another surface.

Tertiary transfer

Occurs when previously transferred trace evidence is transferred again to yet another surface.

Non-contact transfer

Occurs when previously transferred trace evidence is transferred to another surface.

Factors affecting the likelihood of a transfer

What are these?…
1. The nature of the material being transferred
2. The degree to which the material will shed
3. The nature of the receiving surface
4. The nature of the contact
5. The number of times contact is made
6. The size of the area where contact is made

Persistence

The ability of trace evidence to remain on a surface over time, influenced by environmental factors and the nature of the materials involved.

Factors affecting persistence

What are these?…
1. The nature of the accepting surface
2. The addition of certain foreign material on the surface
3. The nature of the transferred material itself
4. What, if any, activity occurred after the transfer?
5. Lifesaving attempts made by medical personnel
6. The environment surround the items in question
7. Time
8. How deeply embedded the material is on the accepting surface
9. The force involved during the transfer

Scientific approach

It is important to take a ______ _______ when working at a crime scene.

Dry them

What should you do with wet items before packaging?

Grid, quadrant

Fill in the blanks:

____ or _______ searches can be used to break down larger areas ensuring all areas are searched effectively.

Lighting and magnification

What two tools are useful for enhancing invisible trace evidence?

Druggist fold

What is this an image of?

False

True or False:
It is easier to collect trace evidence at a crime scene versus a laboratory

Paper bags

How should you package biological evidence?

Vacuum sweeping and tape lifting

What are two of the best ways to collect invisible trace evidence?