2009©Forensic Science Today

Fibers

Collection, Testing and Determination of

Uniqueness

Deedrick, D. W. Hairs, fibers, crime, and evidence, Forensic Science Communications [Online]. (July 2000). Available: http://www.fbi.gov/hq/lab/fsc/backissu/july2000/deedrick.htm.

2009©Forensic Science Today

Types of Fiber

• Natural-– Any fiber that comes

from plant or animal sources, examples?

• Image of cotton fibers. •Deedrick, D. W. Hairs, fibers, crime, and evidence, Forensic Science Communications [Online]. (July 2000). Available: http://www.fbi.gov/hq/lab/fsc/backissu/july2000/deedrick.htm.

2009©Forensic Science Today

Types of Fibers Cont’d

• Synthetic-– Any fiber that is made

in a laboratory, examples?

• Image of nylon.

•Deedrick, D. W. Hairs, fibers, crime, and evidence, Forensic Science Communications [Online]. (July 2000). Available: http://www.fbi.gov/hq/lab/fsc/backissu/july2000/deedrick.htm.

2009©Forensic Science Today

Testing

• Fibers are generally identified by type of cloth and color by

• Physical Properties– Burn test– Melting test– Solubility– Optical properties– Dye identification

2009©Forensic Science Today

Burning and Melting Tests

• Place the fiber in a flame and record the results.

• Heat the fiber on a hotplate and record the results.

• Changes in physical properties: color, smoke, smell, etc.

2009©Forensic Science Today

Solubility Test

• What is it soluble in?

– Strong base

– Strong acid

– other

2009©Forensic Science Today

Optical Properties

• These are the tests that are currently used to identify fibers.

• Behavior in– visible, – IR, – UV and – polarized light • Image from

www.usgs.gov/

2009©Forensic Science Today

Identification of Dye

• Thin Layer Chromatography– Separates molecules based on the affinity to

the surface they are placed on versus their solubility in the solvent they are being dissolved in

– Low solubility in solvent and high adhesion to the surface--- does not go very far

2009©Forensic Science Today• Image from www.dps.state.ia.us

2009©Forensic Science Today

Comparison?• How is the fiber from a scene compared to fiber

from a known source? – All the characteristics found on the known fiber and

the questioned fiber must be identical.

• What does it mean to say they are similar fibers? – Class– Individual

2009©Forensic Science Today

Characteristics

• High probability of linkage with only one individual.

• One of a kind? unusually made fiber made in very small amount with unusual dye

• Consistent with a group

Individual Class

2009©Forensic Science Today

Fiber Collection

• Cellophane tape into Petri dish or

• Vacuuming

• Choose container that will prevent loss

• Label and

• Seal

2009©Forensic Science Today

Comparison of Fibers

• Fibers from victim’s fingernail to known sample from suspect’s sweater.

•

2009©Forensic Science Today

Control Samples

• From victim & suspects’ homes and vehicles

• Uncontaminated

• Large enough to do testing needed