Hair and Fiber Collection

Clothing and other materials are carefully packaged in sealed paper bags and sent to a lab. For extraction, the evidence is taken into a processing room, which provides a clean, sealed environment that is temperature- and humidity-controlled. Hair and fibers are removed through a combination of scraping, picking, vacuum sweeping, combing or clipping. Then, they are placed on glass microscopic slides for identification and comparison.

Experts look at a variety of different physical characteristics of hair, including the shaft diameter, pigment granules and cross-sectional shape. They also examine a hair’s cuticle, the translucent outer layer of the hair shaft consisting of scales, and the medulla, a central core of cells present in some hair types.

DNA Analysis

A small segment of the DNA chain can be isolated and printed on photographic paper. This “print out” of a person’s genetic code can then be used as evidence to connect a suspect to a crime, or maybe to prove his or her innocence.

DNA is found in body fluids. If liquid blood is being collected, a portion of it will be absorbed onto a clean cotton cloth or swab. A portion of the swab or cloth also will be left unstained to use as a control. After the blood has air-dried it is packed in a clean paper envelope with sealed corners. The exact same process is used to collect dried body fluids, only the cloth or swab is first moistened with distilled water. DNA evidence might also be obtained from other sources such as cigarette butts, chewing gum and envelopes and stamps that have been licked.

Fingerprints

Tools for recovering fingerprints include brushes, powders, tape, chemicals, lift cards, a magnifying glass and Super Glue. A crime lab can use fingerprints to identify the victim or identify or rule out a suspect. There are several types of prints a CSI might find at a crime scene:

Visible: Left by the transfer of blood, paint or another fluid or powder onto a surface that is smooth enough to hold the print; evident to the naked eye.

Molded: Left in a soft medium like soap, putty or candle wax, forming an impression.

Latent: Left by the transfer of sweat and natural oils from the fingers onto a surface that is smooth enough to hold the print; not visible to the naked eye.