DNA evidence gaining more acceptance.

Defense attorneys still may challenge the validity of DNA evidence, as has been seen in the O.J. Simpson case, but it is fast becoming an accepted tool for identification, according to the American Chemical Society. DNA profiling compares deoxyribonucleic acid. the material genes are made of, retrieved from a crime scene with that taken from a suspect. The DNA can come from hair, blood, skin, saliva, semen, and other sources. Every individual's DNA is unique (except for that from identical siblings).

Fragments of DNA taken from the crime scene and from the suspect are compared. Generally speaking, if they match, they show that the suspect could be the criminal. Profiling techniques have different sample-size requirements. One method needs a blood stain the size of a dime, while a second requires just one percent of that amount. The first method can take a couple of months; the second, a few days.

While DNA profiling often is used to incriminate suspects, it also has liberated those who are innocent. In Virginia, for example...