SIMPSON MURDER CASE : THE FORENSIC FILE

A look at procedures and processes used in the evaluation of forensic evidence:

Preserving Evidence: Criminalists store damp evidence, such as a bloody glove, in a brown paper bag so that it can dry out. If sealed in a plastic bag, the evidence may putrefy, destroying its value.

Assessing the Blood Evidence: Is it blood? A red stain is treated with hydrogen peroxide to see if it is blood. An enzyme in blood, called peroxidase, releases oxygen from the peroxide. That oxygen reacts with a colorless dye, called phenolphthalein, turning it pink. A similar reaction is seen when peroxide is used to disinfect a cut: Bubbles of oxygen appear.

Determining Time of Death: The most reliable indicator of time of death is body temperature. Coroners know how fast a body cools and thus can tell how long ago death occurred. Rigor mortise, the stiffening of muscles, is useful after the body has cooled, but less accurate. The rate at which body fluids accumulate at the body’s lowest point can also be used to estimate time of death, as well as to indicate if a body has been moved.